Nitric oxide induces angiogenesis and upregulates alpha(v)beta(3) integrin expression on endothelial cells

Multifunctional Microneedle Patches Loaded With Engineered Nitric Oxide-Releasing Nanocarriers for Targeted and Synergistic Chronic Wound Therapy

Chronic wounds impose significant physical and mental burdens on patients. Nano-based formulations offer a promising strategy for chronic wound healing due to their non-invasive nature and enhanced biofilms penetration, but they often lack targeting capability or fail to achieve long-term and synergistic effects. In this work, a multifunctional microneedle (MN) patch loaded with engineered nitric oxide (NO)-releasing nanocarriers are presented that encapsulate an antibacterial agent and are immobilized with Concanavalin A (Con A) and NO molecules for targeted and synergistic treatment of chronic wounds. With the assistance of MNs, the nanoparticles (NPs) can directly cross bacterial biofilms and be efficiently delivered to wound tissues, where they target harmful bacteria through the specific recognition between Con A and polysaccharides on bacterial surfaces, followed by the release of the encapsulated antimicrobial agent, thereby achieving effective antibacterial effect. Moreover, the NPs generate NO in a sustained manner as they dissociate in the wound tissue, which exerts potent anti-inflammatory action and benefits tissue regeneration, further promoting chronic wounds closure. Consequently, this work provides a novel MN patch loaded with engineered NPs designed for accelerating chronic wound healing through targeted and synergistic therapy.

Fabrication and Optimization of Poly(ε-caprolactone) Microspheres Loaded with S-Nitroso-N-Acetylpenicillamine for Nitric Oxide Delivery

Heart disease is one of the leading causes of death in the United States and throughout the world. While there are different techniques for reducing or preventing the impact of heart disease, nitric oxide (NO) is administered as nitroglycerin for reversing angina or chest pain. Unfortunately, due to its gaseous and short-lived half-life, NO can be difficult to study or even administer. Therefore, controlled delivery of NO is desirable for therapeutic use. In the current study, the goal was to fabricate NO-releasing microspheres (MSs) using a donor molecule, S-Nitroso-N-Acetyl penicillamine, (SNAP), and encapsulating it in poly(ε-caprolactone) (PCL) using a single-emulsion technique that can provide sustained delivery of NO to cells over time without posing any toxicity risks. Optimization of the fabrication process was performed by varying the duration of homogenization (5, 10, and 20 min) and its effect on entrapment efficiency and size. The optimized SNAP-MS had an entrapment efficiency of ˃50%. Furthermore, we developed a modified method for NO detection by using NO microsensors to detect the NO release from SNAP-MSs in real time, showing sustained release behavior. The fabricated SNAP-MSs were tested for biocompatibility with HUVECs (human umbilical vein endothelial cells), which were found to be biocompatible. Lastly, we tested the effect of controlled NO delivery to human induced pluripotent stem-derived cardiomyocytes (hiPSC-CMs) via SNAP-MSs, which showed a significant improvement in the electrophysiological parameters and alleviated anoxic stress.

Therapeutic potential of nitric oxide in vascular aging due to the promotion of angiogenesis

The decrease in angiogenesis that occurs with aging significantly contributes to the higher incidence and mortality of cardiovascular diseases among the elderly. This decline in angiogenesis becomes more pronounced with increasing age and is closely linked to abnormal function and senescence of endothelial cells. Enhancing angiogenesis in aging and targeting senescent endothelial cells have gained considerable attention. Nitric oxide (NO) has been thoroughly investigated for its function in regulating angiogenesis and is an important factor that can counteract endothelial cell senescence. This review summarizes the mechanisms of reduced angiogenesis during aging and therapeutic strategies targeting senescent cells. We also discuss the potential of combining the current approaches with NO in promoting angiogenesis in aging vessels.

The role of exercise-induced myokines in promoting angiogenesis

Ischemic diseases are a major cause of mortality or disability in the clinic. Surgical or medical treatment often has poor effect on patients with tissue and organ ischemia caused by diffuse stenoses. Promoting angiogenesis is undoubtedly an effective method to improve perfusion in ischemic tissues and organs. Although many animal or clinical studies tried to use stem cell transplantation, gene therapy, or cytokines to promote angiogenesis, these methods could not be widely applied in the clinic due to their inconsistent experimental results. However, exercise rehabilitation has been written into many authoritative guidelines in the treatment of ischemic diseases. The function of exercise in promoting angiogenesis relies on the regulation of blood glucose and lipids, as well as cytokines that secreted by skeletal muscle, which are termed as myokines, during exercise. Myokines, such as interleukin-6 (IL-6), chemokine ligand (CXCL) family proteins, irisin, follistatin-like protein 1 (FSTL1), and insulin-like growth factor-1 (IGF-1), have been found to be closely related to the expression and function of angiogenesis-related factors and angiogenesis in both animal and clinical experiments, suggesting that myokines may become a new molecular target to promote angiogenesis and treat ischemic diseases. The aim of this review is to show current research progress regarding the mechanism how exercise and exercise-induced myokines promote angiogenesis. In addition, the limitation and prospect of researches on the roles of exercise-induced myokines in angiogenesis are also discussed. We hope this review could provide theoretical basis for the future mechanism studies and the development of new strategies for treating ischemic diseases.

Amorphous Silicon Oxynitrophosphide-Coated Implants Boost Angiogenic Activity of Endothelial Cells

Lack of osteointegration is a major cause of aseptic loosening and failure of implants used in bone replacement. Implants coated with angiogenic biomaterials can improve osteointegration and potentially reduce these complications. Silicon- and phosphorus-based materials have been shown to upregulate expression of angiogenic factors and improve endothelial cell functions. In the present study, we hypothesize that implants coated with amorphous silica-based coatings in the form of silicon oxynitrophosphide (SiONP) by using plasma-enhanced chemical vapor deposition (PECVD) technique could enhance human umbilical vein endothelial cell angiogenic properties in vitro. The tested groups were: glass coverslip (GCS), tissue culture plate, SiON, SiONP1 (O: 7.3 at %), and SiONP2 (O: 14.2 at %) implants. The SiONP2 composition demonstrated 3.5-fold more fibronectin deposition than the GCS (p < 0.001). The SiONP2 group also presented a significant improvement in the capillary tubule length and thickness compared with the other groups (p < 0.01). At 24 h, we observed at least a twofold upregulation of vascular endothelial growth factor A, hypoxia-inducible factor-1α, angiopoietin-1, and nesprin-2, more evident in the SiONP1 and SiONP2 groups. In conclusion, the studied amorphous silica-coated implants, especially the SiONP2 composition, could enhance the endothelial cell angiogenic properties in vitro and may induce faster osteointegration and healing. Impact Statement In this study, we report for the first time the significant enhancement of human umbilical vein endothelial cell angiogenic properties (in vitro) by the amorphous silica-based coatings in the form of silicon oxynitrophosphide (SiONP). The SiONP2 demonstrated 3.5-fold more fibronectin deposition than the glass coverslip and presented a significant improvement in the capillary tubule length and thickness. At 24 h, SiONP reported twofold upregulation of vascular endothelial growth factor A, hypoxia-inducible factor-1α, angiopoietin-1, and nesprin-2. The studied amorphous silica-coated implants enhance the endothelial cell angiogenic properties in vitro and may induce faster osteointegration and healing.

Local pharmacological induction of angiogenesis: Drugs for cells and cells as drugs

The past decades have seen significant advances in pro-angiogenic strategies based on delivery of molecules and cells for conditions such as coronary artery disease, critical limb ischemia and stroke. Currently, three major strategies are evolving. Firstly, various pharmacological agents (growth factors, interleukins, small molecules, DNA/RNA) are locally applied at the ischemic region. Secondly, preparations of living cells with considerable bandwidth of tissue origin, differentiation state and preconditioning are delivered locally, rarely systemically. Thirdly, based on the notion, that cellular effects can be attributed mostly to factors secreted in situ, the cellular secretome (conditioned media, exosomes) has come into the spotlight. We review these three strategies to achieve (neo)angiogenesis in ischemic tissue with focus on the angiogenic mechanisms they tackle, such as transcription cascades, specific signalling steps and cellular gases. We also include cancer-therapy relevant lymphangiogenesis, and shall seek to explain why there are often conflicting data between in vitro and in vivo. The lion's share of data encompassing all three approaches comes from experimental animal work and we shall highlight common technical obstacles in the delivery of therapeutic molecules, cells, and secretome. This plethora of preclinical data contrasts with a dearth of clinical studies. A lack of adequate delivery vehicles and standardised assessment of clinical outcomes might play a role here, as well as regulatory, IP, and manufacturing constraints of candidate compounds; in addition, completed clinical trials have yet to reveal a successful and efficacious strategy. As the biology of angiogenesis is understood well enough for clinical purposes, it will be a matter of time to achieve success for well-stratified patients, and most probably with a combination of compounds.

Gene variants as risk factors for gastroschisis

In a population‐based case‐control study in California of 228 infants, we investigated 75 genetic variants in 20 genes and risk of gastroschisis with regard to maternal age, race/ethnicity, vitamin use, and smoking exposure. We hypothesized that genes related to vascular compromise may interact with environmental factors to affect the risk of gastroschisis. Haplotypes were constructed for 75 gene variants using the HaploView program. Risk for gastroschisis associated with each gene variant was calculated for both the homozygotes and the heterozygotes, with the homozygous wildtypes as the referent. Risks were estimated as odds ratios (ORs) with 95% confidence intervals (CIs) by logistic regression. We found 11 gene variants with increased risk and four variants with decreased risk of gastroschisis for heterozygous (OR_h) or homozygous variants (OR_v) genotypes. These included NOS3 (rs1036145) OR_h = 0.4 (95% CI: 0.2–0.7); NOS3 (rs10277237) OR_v = 2.7 (95% CI: 1.3–6.0); ADD1 (rs12503220) OR_h = 2.9 (95% CI: 1.6–5.4), GNB3 (rs5443) OR_h = 0.2 (95% CI: 0.1–0.5), OR_v = 0.4 (95% CI: 0.2–0.9); ICAM1 (rs281428) OR_v = 6.9 (95% CI: 2.1–22.9), ICAM1 (rs3093030) OR_v = 2.6 (95% CI: 1.2–5.6); ICAM4 (rs281438) OR_v = 4.9 (95% CI: 1.4–16.6), ICAM5 (rs281417) OR_h = 2.1 (95% CI: 1.1–4.1), OR_v = 4.8 (95% CI: 1.7–13.6); ICAM5 (rs281440) OR_h = 23.7 (95% CI: 5.5–102.5), OR_v = 20.6 (95% CI: 3.4–124.3); ICAM5 (rs2075741) OR_v = 2.2 (95% CI: 1.1–4.4); NAT1 OR_v = 0.3 (95% CI: 0.1–0.9). There were additional associations between several gene variants and gastroschisis among women aged 20–24 and among mothers with and without vitamin use. NOS3, ADD1, ICAM1, ICAM4, and ICAM5 warrant further investigation in additional populations and with the interaction of additional environmental exposures. © 2016 Wiley Periodicals, Inc.

Tat PTD-Endostatin-RGD: A novel protein with anti-angiogenesis effect in retina via eye drops

BACKGROUND

Diabetic retinopathy is a leading cause of blindness. The objective was to design a novel fusion protein, Tat PTD-Endostatin-RGD, to treat retinal neovascularization via eye drops instead of traditional intravitreal injection trepapeutical methods.

METHOD

The anti-angiogenesis ability was evaluated in vitro by chick embryo chorioallantoic membrane assay, wound healing assay and tube formation assay. Corneal barrier and blood-retina barrier were constructed in vitro to investigate the penetration ability of Tat PTD-Endostatin-RGD. Western blot was used to detect the integrin αvβ3 expression level in rat retina microvascular endothelial cells which was stimulated by S-nitroso-N-acetylpenicillamine. The binding affinity of Tat PTD-Endostatin-RGD to integrin αvβ3 was investigated by evaluating the penetration ability on blood-retina barriers treated with S-nitroso-N-acetylpenicillamine. The pharmacodynamics and efficacy analysis were further carried out in the oxygen-induced retinopathy model in vivo. In addition, the pharmacokinetic profile via eye drops was studied on a C57BL/6 mice model.

RESULT

Tat PTD-Endostatin-RGD showed high anti-angiogenesis activity and high ability to penetrate these two barriers in vitro. The Western blot results indicated S-nitroso-N-acetylpenicillamine upregulated the expression level of integrin αvβ3 in a dose-dependent manner. Tat PTD-Endostatin-RGD showed a high affinity to rat retina microvascular endothelial cells treated with S-nitroso-N-acetylpenicillamine. The results showed that Tat PTD-Endostatin-RGD could inhibit abnormal angiogenesis in retina via eye drops.

CONCLUSION

Tat PTD-Endostatin-RGD showed high penetration ability through ocular barriers, bound specifically to integrin αvβ3 and effectively inhibited the abnormal angiogenesis.

GENERAL SIGNIFICANCE

Tat PTD-Endostatin-RGD represents a potent novel drug applied via eye drops for fundus oculi neovascularization diseases.

Molecular magnetic resonance imaging of angiogenesis in vivo using polyvalent cyclic RGD-iron oxide microparticle conjugates

Angiogenesis is an essential component of tumour growth and, consequently, an important target both therapeutically and diagnostically. The cell adhesion molecule α(v)β(3) integrin is a specific marker of angiogenic vessels and the most prevalent vascular integrin that binds the amino acid sequence arginine-glycine-aspartic acid (RGD). Previous studies using RGD-targeted nanoparticles (20-50 nm diameter) of iron oxide (NPIO) for magnetic resonance imaging (MRI) of tumour angiogenesis, have identified a number of limitations, including non-specific extravasation, long blood half-life (reducing specific contrast) and low targeting valency. The aim of this study, therefore, was to determine whether conjugation of a cyclic RGD variant [c(RGDyK)], with enhanced affinity for α(v)β(3), to microparticles of iron oxide (MPIO) would provide a more sensitive contrast agent for imaging of angiogenic tumour vessels. Cyclic RGD [c(RGDyK)] and RAD [c(RADyK)] based peptides were coupled to 2.8 μm MPIO, and binding efficacy tested both in vitro and in vivo. Significantly greater specific binding of c(RGDyK)-MPIO to S-nitroso-n-acetylpenicillamine (SNAP)-stimulated human umbilical vein endothelial cells in vitro than PBS-treated cells was demonstrated under both static (14-fold increase; P < 0.001) and flow (44-fold increase; P < 0.001) conditions. Subsequently, mice bearing subcutaneous colorectal (MC38) or melanoma (B16F10) derived tumours underwent in vivo MRI pre- and post-intravenous administration of c(RGDyK)-MPIO or c(RADyK)-MPIO. A significantly greater volume of MPIO-induced hypointensities were found in c(RGDyK)-MPIO injected compared to c(RADyK)-MPIO injected mice, in both tumour models (P < 0.05). Similarly, administration of c(RGDyK)-MPIO induced a greater reduction in mean tumour T(2)* relaxation times than the control agent in both tumour models (melanoma P < 0.001; colorectal P < 0.0001). Correspondingly, MPIO density per tumour volume assessed immunohistochemically was significantly greater for c(RGDyK)-MPIO than c(RADyK)-MPIO injected animals, in both melanoma (P < 0.05) and colorectal (P < 0.0005) tumours. In both cases, binding of c(RGDyK)-MPIO co-localised with α(v)β(3) expression. Comparison of RGD-targeted and dynamic contrast enhanced (DCE) MRI assessment of tumour perfusion indicated sensitivity to different vascular features. This study demonstrates specific binding of c(RGDyK)-MPIO to α(v)β(3) expressing neo-vessels, with marked and quantifiable contrast and rapid clearance of unbound particles from the blood circulation compared to NPIO. Combination of this molecular MRI approach with conventional DCE MRI will enable integrated molecular, anatomical and perfusion tumour imaging.

Calpain 1 and -2 play opposite roles in cord formation of lymphatic endothelial cells via eNOS regulation

Calpains are a family of calcium-dependent proteases. Two isoforms, calpain 1 and 2, have been implicated in angiogenesis and endothelial cell adhesion and migration. Calpains regulate the function of eNOS;however, the relation of calpains and eNOS to lymphangiogenesisis still unclear. In the present study, we evaluated the role of calpain and eNOS in the formation of cords by lymphatic endothelial cells on Matrigel. Human lymphatic microvascular dermal-derived endothelial cells were transfected with siRNA against calpain 1 or 2. Calpain 2 knockdown, but not calpain 1 knockdown, significantly reduced cord formation, adhesion, and migration on Matrigel. These decreases correlated with a reduction in eNOS, and phosphorylated eNOS and Hsp90 levels, as assayed by immunoprecipitation and western blotting. In contrast, the knockdown of calpain 1, but not calpain 2,increased cell adhesion, enhanced migration, and stabilized late-stage cord formation by increasing cord length compared to the control. These differences correlated with an increase in the level of phosphorylated eNOS. The results indicated that the functions of calpains and eNOS are important for cord formation by lymphatic endothelial cells. For the first time, we have found different functions of calpain 1 and 2. Calpain 1 is involved in the degradation of eNOS and Hsp90 and the phosphorylation of eNOS,while calpain 2 regulates eNOS phosphorylation during cord formation by lymphatic endothelial cells on Matrigel.

Role of nitric oxide in placental vascular development and function

Nitric oxide (NO) is one of the most pleiotropic signaling molecules at systemic and cellular levels, participating in vascular tone regulation, cellular respiration, proliferation, apoptosis and gene expression. Indeed NO actively participates in trophoblast invasion, placental development and represents the main vasodilator in this tissue. Despite the large number of studies addressing the role of NO in the placenta, its participation in placental vascular development and the effect of altered levels of NO on placental function remains to be clarified. This review draws a time-line of the participation of NO throughout placental vascular development, from the differentiation of vascular precursors to the consolidation of vascular function are considered. The influence of NO on cell types involved in the origin of the placental vasculature and the expression and function of the nitric oxide synthases (NOS) throughout pregnancy are described. The developmental processes involved in the placental vascular bed are considered, such as the participation of NO in placental vasculogenesis and angiogenesis through VEGF and Angiopoietin signaling molecules. The role of NO in vascular function once the placental vascular tree has developed, in normal pregnancy as well as in pregnancy-related diseases, is then discussed.

Moderate dose insulin promotes function of endothelial progenitor cells

EPCs (endothelial progenitor cells) regenerate the vascular endothelial cells and keep the integrity of the vascular endothelium and thus may retard the onset of atherosclerosis. Steady state levels of EPCs in the circulation were found to be correlated with cardiovascular event risks. Given the close relationship between insulin and the cardiovascular system, we tested the long-term effects of moderate-dose insulin treatment on bone marrow-derived EPCs. Rat bone marrow EPCs were exposed to various levels of insulin under normal (5 mmol/l) or high (40 mmol/l) glucose conditions for 7 days. Insulin at levels near the physiological range (0.1, 1 nmol/l) up-regulated EPCs proliferation, stimulated NO (nitric oxide) production and reduced EPC senescence and ROS (reactive oxygen species) generation under both normal- and high-glucose conditions. Glucose exerted deleterious effects on EPCs contrary to insulin. Western blot analysis suggested concomitant decrease of Akt phosphorylation and eNOS (endothelial nitric oxide synthase) expression by high-glucose treatment and increase with insulin administration. Thus, insulin promoted several activities of EPCs, which suggested a potential endothelial protective role of insulin. Akt/eNOS pathway may be involved in the modulation of EPCs function by glucose and insulin.

Adult skeletal muscle stem cell migration is mediated by a blebbing/amoeboid mechanism

Adult skeletal muscle possesses a resident stem cell population called satellite cells, which are responsible for tissue repair following damage. Satellite cell migration is crucial in promoting rapid tissue regeneration, but it is a poorly understood process. Furthermore, the mechanisms facilitating satellite cell movement have yet to be elucidated. This study investigates the process of satellite cell migration, revealing that they undergo two distinct phases of movement, first under the basal lamina and then rapidly increasing their velocity when on the myofiber surface. Most significantly, we show that satellite cells move using a highly dynamic blebbing or amoeboid-based mechanism and not via lamellipodia-mediated propulsion. We show that nitric oxide and noncanonical Wnt signaling pathways are necessary for regulating the formation of blebs and the migration of satellite cells. In summary, we propose that the formation of blebs and their necessity for satellite cell migration has significant implications in the future development of therapeutic regimes aimed at promoting skeletal muscle regeneration.

Collagen IV contributes to nitric oxide-induced angiogenesis of lung endothelial cells

Nitric oxide (NO) mediates endothelial angiogenesis via inducing the expression of integrin α(v)β(3). During angiogenesis, endothelial cells adhere to and migrate into the extracellular matrix through integrins. Collagen IV binds to integrin α(v)β(3), leading to integrin activation, which affects a number of signaling processes in endothelial cells. In the present study, we evaluated the role of collagen IV in NO-induced angiogenesis. We found that NO donor 2,2'-(hydroxynitrosohydrazino)bis-ethanamine (NOC-18) causes increases in collagen IV mRNA and protein in lung endothelial cells and collagen IV release into the medium. Addition of collagen IV into the coating of endothelial culture increases endothelial monolayer wound repair, proliferation, and tube formation. Inhibition of collagen IV synthesis using gene silencing attenuates NOC-18-induced increases in monolayer wound repair, cell proliferation, and tube formation as well as in the phosphorylation of focal adhesion kinase (FAK). Integrin blocking antibody LM609 prevents NOC-18-induced increase in endothelial monolayer wound repair. Inhibition of protein kinase G (PKG) using the specific PKG inhibitor KT5823 or PKG small interfering RNA prevents NOC-18-induced increases in collagen IV protein and mRNA and endothelial angiogenesis. Together, these results indicate that NO promotes collagen IV synthesis via a PKG signaling pathway and that the increase in collagen IV synthesis contributes to NO-induced angiogenesis of lung endothelial cells through integrin-FAK signaling. Manipulation of collagen IV could be a novel approach for the prevention and treatment of diseases such as alveolar capillary dysplasia, severe pulmonary arterial hypertension, and tumor invasion.

Preventing negative effects of smoking on microarterial anastomosis

Although microsurgery has rapid expanded, problems related to microarterial anastomosis continue. Cigarette smoking is one of the major risks for anastomosis by increasing platelet adhesion, and its effects on endothelial cells. Aim of this article is to study the negative effects of cigarettes on microarterial anastomosis line, and to investigate the protective effects of recombinant human erythropoietin (rHuEPO).Ninety-six Sprague-Dawley male rats were divided into 3 groups: group 1 was the control. Rats in groups 2 and 3 were exposed to cigarette smoke starting 21 days prior to surgery for 3 times a day. In group 3, additional 150 IU/kg rHuEPO was given via subcutaneously every 48 hours after microvascular anastomosis, femoral arterial samples, and blood samples were taken for assessment at 1st, 3rd, 5th, and 7th day. Intimae/media ratios were calculated for morphologic analyses.On morphologic analysis of femoral arteries there were statistically significant differences for all 3 groups at 1st, 3rd, 5th, and 7th days (P < 0, 05). The group that made differences was group 2, according to one-way analysis of variance within 3 groups in all days.Smoking decreases endothelial cells healing and causes more thromboses. rHuEPO can prevent these negative effects of smoking.

Mediators of ocular angiogenesis

Angiogenesis is the formation of new blood vessels from pre-existing vasculature. Pathologic angiogenesis in the eye can lead to severe visual impairment. In our review, we discuss the roles of both pro-angiogenic and anti-angiogenic molecular players in corneal angiogenesis, proliferative diabetic retinopathy, exudative macular degeneration and retinopathy of prematurity, highlighting novel targets that have emerged over the past decade.

VEGFR1 (Flt1) regulates Rab4 recycling to control fibronectin polymerization and endothelial vessel branching

The cell's main receptor for VEGF, VEGFR2 (Kdr) is one of the most important positive regulators of new blood vessel growth and its downstream signalling is well characterized. By contrast, VEGFR1 (Flt1) and the mechanisms by which this VEGF receptor promotes branching morphogenesis in angiogenesis remain relatively unclear.Here we report that engagement of VEGFR1 activates a Rab4A-dependent pathway that transports alphavbeta3 Integrin from early endosomes to the plasma membrane, and that this is required for VEGF-driven fibronectin polymerization in endothelial cells. Furthermore, VEGFR1 acts to promote endothelial tubule branching in an organotypic model of angiogenesis via a mechanism that requires Rab4A and alphavbeta3 Integrin. We conclude that a recycling pathway regulated by Rab4A is a critical effector of VEGFR1 during branching morphogenesis of the vasculature.

Molecular mechanisms of pulmonary hypertension

The pathogenesis of pulmonary arterial hypertension (PAH) is complex, involving multiple modulating genes and environmental factors. Multifactorial impairment of the physiologic balance can lead to vasoconstriction, vascular smooth muscle cell and endothelial cell proliferation/fibrosis, inflammation, remodeling and in-situ thrombosis. These are the likely mechanisms that lead to narrowing of the vessel followed by progressive increase in pulmonary vascular resistance and the clinical manifestations of pulmonary hypertension. Subsequently, major goal of the therapy is to avoid acute pulmonary vasoconstriction, halt the progression of vascular remodeling, and reverse the early vascular remodeling if possible. Recently published data addressing certain molecular mechanisms for pathogenesis of PAH have led to the successful therapeutic interventions. This review will focus on the common and critical molecular pathways including genetic basis of the development of PAH that on the whole may be new targets for therapeutic interventions.

Angiotensin II promotes NO production, inhibits apoptosis and enhances adhesion potential of bone marrow-derived endothelial progenitor cells

Endothelial progenitor cells (EPCs) participate in the processes of postnatal neovascularization and re-endothelialization in response to tissue ischemia and endothelial injury. The level of EPCs present has been found to be directly associated with the outcome of cardiovascular diseases, and could be regulated by stimulatory or inhibitory factors. Given the close relationship between angiotensin II (AngII) and the cardiovascular system, we investigated the effect of AngII on the activities of bone marrow (BM)-derived EPCs. Cells were isolated from BM of rats by density gradient centrifugation. Administration of AngII significantly promoted nitric oxide (NO) release, inhibited EPC apoptosis and enhanced EPC adhesion potential. All of these AngII-mediated effects on EPCs were attenuated by pretreatment with valsartan or L-NAME. Moreover, both LY294002 and wortmannin abolished the anti-apoptotic effect of AngII. Western blot analyses indicated that endothelial NO synthase (eNOS) protein and phosphorylated Akt increased with the treatment of AngII in EPCs. Thus, AngII improved several activities of EPCs through AngII type 1 receptor (AT1R), which may represent a possible mechanism linking AngII and AT1R with angiogenesis. Additionally, AngII-induced NO synthesis through eNOS in EPCs regulates apoptosis and adhesion, and the PI3-kinase/Akt pathway has an essential role in AngII-induced antiapoptosis signaling.

Neurorestorative treatment of stroke: cell and pharmacological approaches

There is a compelling need to develop cell and pharmacological therapeutic approaches to be administered beyond the hyperacute phase of stroke. These therapies capitalize on the capacity of the brain for neuroregeneration and neuroplasticity and are designed to reduce neurological deficits after stroke. This review provides an update of bone marrow-derived mesenchymal stem cells (MSCs) and select pharmacological agents in clinical use for other indications that promote the recovery process in the subacute and chronic phases after stroke. Among these agents are 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (statins), erythropoietin (EPO), and phosphodiesterase type 5 (PDE-5) inhibitors and nitric oxide (NO) donors. Both the MSCs and the pharmacologic agents potentiate brain plasticity and neurobehavioral recovery after stroke.

Cigarette smoke exposure impairs VEGF-induced endothelial cell migration: role of NO and reactive oxygen species

Endothelial dysfunction is one of the earliest pathological effects of cigarette smoking. Vascular endothelial growth factor (VEGF) has been shown to be an important regulator of endothelial healing and growth. Accordingly, we tested the hypothesis that cigarette smoke exposure impairs VEGF actions in endothelial cells. In human umbilical vein endothelial cells (HUVECs), cigarette smoke extracts (CSE) inhibited VEGF-induced tube formation in the matrigel assay. CSE did not affect HUVECs proliferation, but significantly reduced cellular migration in response to VEGF. This impaired migratory activity was associated with a reduced expression of alpha(v)beta(3), alpha(v)beta(5), alpha(5)beta(1) and alpha(2)beta(1) integrins. The Akt/eNOS/NO pathway has been shown to be important for VEGF-induced endothelial cell migration. We found that CSE inhibited Akt/eNOS phosphorylation and NO release in VEGF-stimulated HUVECs. This was associated with an increased generation of reactive oxygen species (ROS). Importantly, in HUVECs exposed to CSE, treatment with antioxidants (NAC, vitamin C) reduced ROS formation and rescued VEGF-induced NO release, cellular migration and tube formation. Moreover, treatment with NO donors (SNAP, SNP) or a cGMP analog (8-Br-cGMP) rescued integrin expression, cellular migration and tube formation in endothelial cells exposed to CSE. (1) Cigarette smoke exposure impairs VEGF-induced endothelial cell migration and tube formation. (2) The mechanism involves increased generation of ROS, decreased expression of surface integrins together with a blockade of the Akt/eNOS/NO pathway. (3) These findings could contribute to explain the negative effect of cigarette smoking on endothelial function and vessel growth.

Calpain‐2 regulation of VEGF‐mediated angiogenesis

Angiogenesis is a complex process involving endothelial cell migration, proliferation, and differentiation as well as tube formation. These processes are stimulated by a variety of growth factors such as vascular endothelial growth factor (VEGF). VEGF-induced cytoskeletal reorganization plays a crucial role in the angiogenic processes. In the present study, we evaluated the role of calpain in VEGF-induced angiogenesis in vitro and in vivo. Human pulmonary microvascular endothelial cells (PMEC) were incubated with VEGF (10-60 ng/ml) for 2-24 h, after which we measured calpain activities, protein contents of the calpain subunits and of calpastatin, endothelial monolayer wound repair, tube formation, and actin cytoskeleton changes. Incubation of PMEC with VEGF resulted in dose- and time-dependent increases in calpain activity and protein content of calpain-2. VEGF did not change the protein contents of calpain-1 and the small subunit or of calpastatin. Incubation of PMEC with a VEGF receptor blocker prevented the VEGF-induced increase in calpain activity. Inhibition of calpain activity by siRNA directed against calpain-2 and by overexpression of calpastatin prevented VEGF-induced increases in actin stress fibers in endothelial cells and angiogenesis. Overexpression of calpastatin also inhibits vessel formation in subcutaneous (s.c.) matrigel plugs in mice. These results indicate that calpain mediates VEGF-induced angiogenic effects by modulating actin cytoskeletal organization.

Insulin prevents oxidant-induced endothelial cell barrier dysfunction via nitric oxide-dependent pathway

BACKGROUND

The rigorous maintenance of normoglycemia by the administration of insulin is beneficial to critically ill patients. Because insulin induces endothelial nitric oxide (NO) release, and the constitutive release of NO maintains normal microvascular permeability, the authors postulated that insulin would prevent peroxide (H(2)O(2))-induced endothelial barrier dysfunction, an effect dependent on endothelial NO synthase (eNOS) activity.

METHODS

Murine lung microvascular endothelial cells (LMEC) grown to confluence on 8 micro pore polyethylene filters were exposed to media (control), H(2)O(2) (20 to 500 micromol/L), insulin (1 to 1,000 nmol/L) or insulin (100 nmol/L) + H(2)O(2) (10(-4)mol/L). Endothelial monolayer permeability was quantitated by measuring the transendothelial electrical resistance at 15-minute intervals for 120 minutes. Other cells were exposed to H(2)O(2) and insulin after pretreatment with a NO scavenger (PTIO), an eNOS inhibitor (L-NIO), or a phosphoinositol-3-kinase inhibitor (LY-294002).

RESULTS

H(2)O(2) caused a concentration- and time-dependent reduction in electrical resistance consistent with an increase in monolayer permeability. This effect was prevented by insulin. Inhibiting NO release (L-NIO, LY-294002) or scavenging NO (PTIO) abolished this protective effect.

CONCLUSIONS

These data suggest that insulin may modulate endothelial barrier function during oxidant stress by inducing the release of NO.

Modulation of endothelial cell migration by extracellular nucleotides: involvement of focal adhesion kinase and phosphatidylinositol 3-kinase-mediated pathways

Extracellular nucleotides bind to type-2 purinergic/pyrimidinergic (P2) receptors that mediate various responses, such as cell activation, proliferation and apoptosis, implicated in inflammatory processes. The role of P2 receptors and their associated signal transduction pathways in endothelial cell responses has not been fully investigated. Here, it is shown that stimulation of human umbilical vein endothelial cells (HUVEC) with extracellular ATP or UTP increased intracellular free calcium ion concentrations ([Ca(2+)](i)), induced phosphorylation of focal adhesion kinase (FAK), p130(cas) and paxillin, and caused cytoskeletal rearrangements with consequent cell migration. Furthermore, UTP increased migration of HUVEC in a phosphatidylinositol 3-kinase (PI3-K)-dependent manner. BAPTA or thapsigargin inhibited the extracellular nucleotide-induced increase in [Ca(2+)](i), a response crucial for both FAK phosphorylation and cell migration. Furthermore, long-term exposure of HUVEC to ATP and UTP, agonists of the G protein-coupled P2Y2 and P2Y4 receptor subtypes, caused upregulation of alpha(v) integrin expression, a cell adhesion molecule known to directly interact with P2Y2 receptors. Our results suggest that extracellular nucleotides modulate signaling pathways in HUVEC influencing cell functions, such as cytoskeletal changes, cellular adhesion and motility, typically associated with integrin-activation and the action of growth factors. We propose that P2Y2 and possibly P2Y4 receptors mediate those responses that are important in vascular inflammation, atherosclerosis and angiogenesis.

Regulation of VEGF and bFGF mRNA expression and other proliferative compounds in skeletal muscle cells

The role of muscle contraction, prostanoids, nitric oxide and adenosine in the regulation of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and endothelial cell proliferative compounds in skeletal muscle cell cultures was examined. VEGF and bFGF mRNA, protein release as well as the proliferative effect of extracellular medium was determined in non-stimulated and electro-stimulated rat and human skeletal muscle cells. In rat skeletal muscle cells these aspects were also determined after treatment with inhibitors and/or donors of nitric oxide (NO), prostanoids and adenosine. Electro-stimulation caused an elevation in the VEGF and bFGF mRNA levels of rat muscle cells by 33% and 43% (P < 0.05), respectively, and in human muscle cells VEGF mRNA was elevated by 24%. Medium from electro-stimulated human, but not rat muscle cells induced a 126% higher (P < 0.05) endothelial cell proliferation than medium from non-stimulated cells. Cyclooxygenase inhibition of rat muscle cells induced a 172% increase (P < 0.05) in VEGF mRNA and a 104% increase in the basal VEGF release. Treatment with the NO donor SNAP (0.5 microM) decreased (P < 0.05) VEGF and bFGF mRNA by 42 and 38%, respectively. Medium from SNAP treated muscle cells induced a 45% lower (P < 0.05) proliferation of endothelial cells than control medium. Adenosine enhanced the basal VEGF release from muscle cells by 75% compared to control. The present data demonstrate that contractile activity, NO, adenosine and products of cyclooxygenase regulate the expression of VEGF and bFGF mRNA in skeletal muscle cells and that contractile activity and NO regulate endothelial cell proliferative compounds in muscle extracellular fluid.

Pathological angiogenesis is reduced by targeting pericytes via the NG2 proteoglycan

The NG2 proteoglycan is expressed by nascent pericytes during the early stages of angiogenesis. To investigate the functional role of NG2 in neovascularization, we have compared pathological retinal and corneal angiogenesis in wild type and NG2 null mice. During ischemic retinal neovascularization, ectopic vessels protruding into the vitreous occur twice as frequently in wild type retinas as in NG2 null retinas. In the NG2 knock-out retina, proliferation of both pericytes and endothelial cells is significantly reduced, and the pericyte:endothelial cell ratio falls to 0.24 from the wild type value of 0.86. Similarly, bFGF-induced angiogenesis is reduced more than four-fold in the NG2 null cornea compared to that seen in the wild type retina. Significantly, NG2 antibody is effective in reducing angiogenesis in the wild type cornea, suggesting that the proteoglycan can be an effective target for anti-angiogenic therapy. These experiments therefore demonstrate both the functional importance of NG2 in pericyte development and the feasibility of using pericytes as anti-angiogenic targets.

Gender and estrogen supplementation increases severity of experimental choroidal neovascularization

Observational clinical studies suggest that post-menopausal women may be at risk for more severe age-related macular degeneration, and that estrogen loss due to menopause may contribute. We sought to determine the effect of gender and estrogen status on the severity of choroidal neovascularization (CNV) in a mouse model for experimental choroidal neovascularization. Laser-induced CNV was performed in mice with or without estrogen supplementation. At various times, eyes were removed for analysis of severity of CNV lesions or for extraction of choroidal mRNA to evaluate iNOS, TNF-alpha, MMP-9, and ER-alpha expression, which are molecules relevant to angiogenic processes. Also, splenic macrophages were analysed for iNOS to determine the effect of estrogen treatment in vitro. Finally, laser-induced CNV was performed in iNOS -/- mice. Our result showed that aged female mice had significantly larger CNV than age-matched males. Ovariectomy in adult mice did not increase severity, but paradoxically estrogen supplementation after ovariectomy did increase CNV severity. More severe CNV were associated with a significant decrease in choroidal iNOS mRNA. Splenic macrophages from estrogen supplemented mice showed a significant increased in TNF-alpha mRNA expression (eight fold difference compared to the control) but only a mild change in iNOS mRNA levels (2-3 fold difference). In vitro data further showed that nitric oxide production in splenic macrophages at different estrogen levels was not different from controls. Finally, CNV severity was significantly more severe in iNOS -/- mice, compared to iNOS +/+ mice after laser treatment. In conclusion, aged female mice developed more severe CNV than do males. Estrogen replacement seems to increase severity, possibly by suppressing the upregulation of choroidal iNOS and activating macrophages. The putative beneficial or detrimental role of estrogen biology in age-related macular degeneration must be more carefully evaluated and may vary with the stage of age-related macular degeneration (atrophic or neovascular) as well as with the specific target cell type (monocytes vs. endothelial cell or vascular smooth muscle cell).

Stimulation of in vitro angiogenesis by nitric oxide through the induction of transcription factor ETS-1

The aim of this study was to examine whether transcription factor ETS-1, which is responsible for the expression of metalloproteinases and integrin beta(3), is implicated in the induction of nitric oxide (NO)-induced angiogenesis. Bovine aortic endothelial cells were cultured on type I collagen gel to measure the length of the formed tube-like structure, which is a marker for in vitro angiogenesis. The addition of S-nitroso-N-acetylpenicillamine (SNAP), an NO-donor, to confluent endothelial cells stimulated the formation of the tube-like structure, with disappearance of covered endothelial cell monolayers. Another NO-donor 2,2'-(hydroxynitrosohydrazono)bis-ethanamine (NOC 18) also induced the formation of the tube-like structure. In contrast to the induction of the formation of the tube-like structure by SNAP, it reduced cell proliferation. SNAP and NOC 18 also increased the expression of the ets-1 mRNA level in a concentration-dependent manner. The maximum expression was observed at 2h after their addition. Moreover, the SNAP-induced in vitro angiogenesis, ets-1 mRNA expression and ETS-1 protein expression were strongly reduced by the treatment with ets-1 antisense oligonucleotide. These results strongly suggest that NO stimulates in vitro angiogenesis through the induction of ETS-1 expression. NO appears to stimulate endothelial cell differentiation to the angiogenic phenotype via the induction of ETS-1 transcription factor.

Establishment of an immortalized human-liver endothelial cell line with SV40T and hTERT

BACKGROUND AND AIMS

Liver endothelial cells (LECs) perform an essential role in important pathophysiologic functions in the liver. Establishment of a human LEC line facilitates advances in LEC research. Here, we present immortalization of human LECs using retroviral gene transfer of simian virus 40 large T antigen (SV40T) and human telomerase reverse transcriptase (hTERT). We also demonstrate excision of SV40T and hTERT with TAT-mediated Cre/loxP recombination and subsequent cell sorting.

METHODS

First, human LECs were transduced with a retroviral vector somatostatin receptor (SSR)#69 expressing SV40T and hygromycin-resistance genes flanked by a pair of loxA recombination targets. Then, cells were retrovirally superinfected with SSR#197 encoding hTERT and green fluorescent protein (GFP) cDNAs that were intervened by two loxBs. One SV40T-and hTERT-immortalized LEC clone, TMNK-1, was established and analyzed for its biologic characteristics.

RESULTS

The cells were hygromycin-resistant and uniformly positive for GFP expression. TMNK-1 expressed EC markers, including factor VIII, vascular endothelial growth factor receptors (flt-1, KDR/Flk-1), and CD34, showed uptake of Di-I-acetylated-low-density lipoprotein and angiogenic potential in Matrigel assays. After lipopolysaccharide treatment, TMNK-1 produced tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 and exhibited increased expression of intra-cellular adhesive molecule-1, vascular cellular adhesive molecule-1, and VE-cadherin. After treatment with TAT-Cre recombinase fusion protein, approximately 60% of TMNK-1 was negative for GFP expression, and subsequent cell sorting of this population for GFP allowed for collection of the reverted form of TMNK-1.

CONCLUSIONS

This study demonstrates the utility and efficiency of the reversible immortalization procedure to expand primary human LECs for basic studies.

Inducible nitric oxide synthase and vascular endothelial growth factor are colocalized in the retinas of human subjects with diabetes

PURPOSE

Nitric oxide (NO) mediates vascular endothelial growth factor (VEGF)-induced angiogenesis and vascular hyperpermeability. This study was undertaken to study the cellular distribution of inducible nitric oxide synthase (iNOS) and VEGF in the retinas from human subjects with diabetes mellitus. In addition, glial reactivity and peroxynitrite generation were detected by immunolocalization of glial fibrillary acidic protein (GFAP) and nitrotyrosine, respectively.

METHODS

Eight post-mortem eyes from four consecutive subjects with diabetes mellitus and eight eyes from four subjects without diabetes and without known ocular disease were prospectively collected and examined. We used immunohistochemical techniques and antibodies directed against iNOS, VEGF, GFAP, and nitrotyrosine.

RESULTS

In retinas from all subjects without diabetes, weak GFAP immunoreactivity was confined to nerve fibre and ganglion cell layers. There was no immunoreactivity for iNOS, nitrotyrosine, and VEGF. All diabetic retinas showed GFAP induction in Müller cells and GFAP upregulation in nerve fibre and ganglion cell layers. All diabetic retinas showed cytoplasmic immunoreactivity for iNOS, and VEGF in ganglion cells, cells in the inner nuclear layer, and glial cells. In serial sections, ganglion cells and cells in the inner nuclear layer expressing VEGF were localized in the same area of iNOS-expressing ganglion cells and cells in the inner nuclear layer. Six retinas from three subjects with diabetes showed immunoreactivity for nitrotyrosine in vascular endothelial cells in inner retinal layer.

CONCLUSIONS

iNOS and VEGF are colocalized in diabetic retinas. Increased GFAP immunoreactivity is a pathological event in the retina during diabetes.

Effect of shear stress on microvessel network formation of endothelial cells with in vitro three-dimensional model

Shear stress stimulus is expected to enhance angiogenesis, the formation of microvessels. We determined the effect of shear stress stimulus on three-dimensional microvessel formation in vitro. Bovine pulmonary microvascular endothelial cells were seeded onto collagen gels with basic fibroblast growth factor to make a microvessel formation model. We observed this model in detail using phase-contrast microscopy, confocal laser scanning microscopy, and electron microscopy. The results show that cells invaded the collagen gel and reconstructed the tubular structures, containing a clearly defined lumen consisting of multiple cells. The model was placed in a parallel-plate flow chamber. A laminar shear stress of 0.3 Pa was applied to the surfaces of the cells for 48 h. Promotion of microvessel network formation was detectable after approximately 10 h in the flow chamber. After 48 h, the length of networks exposed to shear stress was 6.17 (+/-0.59) times longer than at the initial state, whereas the length of networks not exposed to shear stress was only 3.30 (+/-0.41) times longer. The number of bifurcations and endpoints increased for networks exposed to shear stress, whereas the number of bifurcations alone increased for networks not exposed to shear stress. These results demonstrate that shear stress applied to the surfaces of endothelial cells on collagen gel promotes the growth of microvessel network formation in the gel and expands the network because of repeated bifurcation and elongation.

Adenoviral Gene Transfer of the Human Inducible Nitric Oxide Synthase Gene Enhances the Radiation Response of Human Colorectal Cancer Associated with Alterations in Tumor Vascularity

Nitric oxide is a potent radiosensitizer of tumors, but its use clinically is limited by serious side effects when administered systemically. We have demonstrated previously that gene transfer of the inducible nitric oxide synthase gene (iNOS) into colorectal cancer cells enhances radiation-induced apoptosis in vitro. The objectives of this study were to further characterize the effects of iNOS gene transfer on the radiosensitivity of human colorectal cancer cells in vitro and tumors grown in athymic nude mice. Adenoviral gene transfer of iNOS (AdiNOS) into human colorectal cancer cell lines (HCT-116 and SNU-1040 cells) significantly enhanced the effects of radiation with sensitizing enhancement ratios (0.1) of 1.65 and 1.6, respectively. The radiation enhancement induced by iNOS was associated with increased iNOS expression and nitric oxide production and prevented by L-NIO, an enzymatic inhibitor of iNOS. AdiNOS treatment of HCT-116 tumors combined with radiation (2 Gy x three fractions) led to a 3.4-fold greater (P < 0.005) tumor growth delay compared with radiation (RT) alone. AdiNOS plus RT also caused significant (P < 0.01) tumor regression with 63% of tumors regressing compared with only 6% of tumors treated with RT. AdiNOS plus RT significantly (P < or = 0.001) increased the percentage of apoptotic cells (22 +/- 4%) compared with either tumors treated with control vector plus RT (9 +/- 1%), AdiNOS alone (9 +/- 3%), or no treatment (2 +/- 1%). These radiosensitizing effects of AdiNOS occurred at low infection efficiency (4% of tumor infected), indicating a significant bystander effect.

Local RAD50 gene delivery induces regression of preformed porcine coronary in-stent neointimal hyperplasia

BACKGROUND

Recently, we observed that overexpression of human RAD50 (hRAD50) induced p21-dependent cytotoxicity in various cultured cells, and rat and mouse tumor models. This study investigated the characteristics of endothelial cell (EC) death by hRAD50 and the potential utility of hRAD50 in the development of gene therapies for vascular restenosis.

METHODS

We studied the effects of transient hRAD50 gene transfer using nonliposomal lipid on the survival of primary cultured human coronary arterial EC and smooth muscle cells (SMC). Palmaz-Schatz stents were deployed in two epicardial coronary arteries in each pig (n = 10). Two weeks later, the patency of the stented arteries was documented by coronary angiography, and the hRAD50 construct or empty vector mixed with lipid was delivered to one of the stented arteries in each pig using a Dispatch catheter. Coronary angiography was repeated 2 weeks after gene delivery and histological examination was performed.

RESULTS

Lipid-mediated hRAD50 gene transfer resulted in the death of EC and SMC. It also increased endothelial nitric oxide synthase (eNOS) expression and nitrite production as well as p21 expression. Pretreatment with NOS and pan-caspase inhibitors completely prevented EC death by hRAD50. In the hRAD50-delivered arteries, the percentage of diameter stenosis, neointimal area, and pathologic area of stenosis were significantly smaller than in the control arteries. eNOS expression increased in the hRAD50-delivered arteries. Systemic hematologic and chemical values were not affected by gene delivery.

CONCLUSIONS

Significant regression of preformed in-stent neointimal hyperplasia was induced by local hRAD50 gene delivery to stented porcine coronary arteries without apparent systemic toxicity.

Age-related macular degeneration: etiology, pathogenesis, and therapeutic strategies

Age-related macular degeneration is the principal cause of registered legal blindness among those aged over 65 in the United States, western Europe, Australia, and Japan. Despite intensive research, the precise etiology of molecular events that underlie age-related macular degeneration is poorly understood. However, investigations on parallel fronts are addressing this prevalent public health problem. Sophisticated biochemical and biophysical techniques have refined our understanding of the pathobiology of drusen, geographic atrophy, and retinal pigment epithelial detachments. Epidemiological identification of risk factors has facilitated an intelligent search for underlying mechanisms and fueled clinical investigation of behavior modification. Gene searches have not only brought us to the cusp of identifying the culpable gene loci in age-related macular degeneration, but also localized genes responsible for other macular dystrophies. Recent and ongoing investigations, often cued by tumor biology, have revealed an important role for various growth factors, particularly in the neovascular form of the condition. Transgenic and knockout studies have provided important mechanistic insights into the development of choroidal neovascularization, the principal cause of vision loss in age-related macular degeneration. This in turn has culminated in preclinical and clinical trials of directed molecular interventions.

Noninvasive assessment of angiogenesis by ultrasound and microbubbles targeted to alpha(v)-integrins

BACKGROUND

Noninvasive methods for characterizing neovessel formation during angiogenesis are currently lacking. We hypothesized that angiogenesis could be imaged with the use of contrast-enhanced ultrasound (CEU) with microbubbles targeted to alpha(v)-integrins.

METHODS AND RESULTS

Microbubbles targeted to alpha(v)-integrins were prepared by conjugating echistatin (MB(E)) or monoclonal antibody against murine alpha(v) (MB(alpha)) to their surface. Control microbubbles (MB(c)) were also prepared. The microvascular behavior of these microbubbles was assessed by intravital microscopy of the cremaster muscle in mice treated for 4 days with sustained-release FGF-2. Microvascular retention was much greater (P<0.01) for MB(E) (11+/-6 mm(-3)) and MB(alpha) (10+/-7 mm(-3)) than that for MB(c) (1+/-1 mm(-3)). Retained MB(E) and MB(alpha) attached directly to the microvascular endothelial surface. Microbubble retention in 4 control mice was minimal. Subcutaneous matrigel plugs enriched with FGF-2 were created in 12 mice and studied 10 days later. Neovessels within the matrigel stained positive for alpha(v)-integrins. CEU demonstrated greater (P<0.01) acoustic intensity for MB(E) (16.0+/-5.9 U) and MB(alpha) (17.0+/-5.5 U) compared with MB(c) (5.8+/-2.6 U). The signal from targeted microbubbles (MB(E) and MB(alpha)) correlated well (r=0.90) with the matrigel blood volume determined by CEU perfusion imaging.

CONCLUSIONS

CEU with microbubbles targeted for alpha(v)-integrins may provide a noninvasive method for assessing therapeutic angiogenesis.

Arteriolar flow recruitment with vitronectin receptor stimulation linked to remote wall shear stress

Our purpose was to investigate the hemodynamic mechanism of flow recruitment within arteriolar networks as stimulated by the vitronectin receptor. Since remote stimulation of the vitronectin receptor initiates a flow-mediated dilation, we tested whether the response could be mimicked by exogenous NO. Arteriolar diameter, red blood cell flux, and velocity were measured in terminal branch arterioles arising from a central feed (8-10 microm) arteriole (together previously defined as an arteriolar network) in the cheek pouch tissue of anesthetized hamsters (n = 29, pentobarbital 70 mg/kg). Terminal branch arterioles were stimulated (micropipette, 10 s) with 10 microg/ml LM609 (agonist, vitronectin receptor), 10(-4) M nitroprusside (SNP), or control. The same amount of flow was recruited into the network by applying LM609 or SNP to only one branch of the network; however, flow distribution differed. With LM609, all recruited flow went directly to the branch that was stimulated. With SNP, recruited flow was distributed evenly throughout the network, no matter where the stimulus was applied. Thus, flow-mediated dilation induced by vitronectin receptor stimulation initiates a robust flow recruitment response, directing flow to the stimulus flow path. In contrast, NO alone initiates flow recruitment to the entire network, along multiple parallel flow paths.

Constitutive and inducible nitric oxide synthase: role in angiogenesis

Since the initial report of nitric oxide (NO) activity, enormous progress has been made over the last two decades in the field of NO research. Whereas most physiological responses triggered by moderate concentrations of NO are mediated by soluble guanylate cyclase activation and the subsequent production of cyclic GMP as the major signaling messenger, recent studies have provided evidence of alternative signaling pathways triggered by high concentrations of NO. These signals operate in part through redox-sensitive regulation of transcription factors, gene expression, transcription, cellular activation, proliferation, and cell death. Numerous results converge to indicate a role for NO in physiological and pathological angiogenesis. Experimental data indicate that NO synthase, depending on the isoforms, the timing, and the degree of activation, may display contradictory effects, expressed during both physiological and pathological angiogenesis. The dual personality of NO will be reviewed in the context of the angiogenesis process.

Blockade of nitric-oxide synthase reduces choroidal neovascularization

Nitric oxide (NO) promotes retinal and choroidal neovascularization, although different isoforms of nitric-oxide synthetase (NOS) are critical in each. Deficiency of endothelial NOS (eNOS) suppresses retinal but not choroidal neovascularization, whereas deficiency of neuronal NOS (nNOS) or inducible NOS (iNOS) suppresses choroidal, but not retinal neovascularization. In this study, we investigated the effect of N(G)-monomethyl-L-arginine (L-NMMA), a nonspecific NOS inhibitor, in three models of ocular neovascularization. Oral administration of L-NMMA caused significant inhibition of choroidal neovascularization in mice with laser-induced rupture of Bruch's membrane and significantly inhibited subretinal neovascularization in transgenic mice with expression of vascular endothelial growth factor (VEGF) in photoreceptors (rho/VEGF mice) but did not inhibit retinal neovascularization in mice with ischemic retinopathy. By extensive mating among mice deficient in NOS isoforms, triple homozygous mutant mice deficient in all three NOS isoforms were produced. These mice had marked suppression of choroidal neovascularization at sites of rupture of Bruch's membrane and near-complete suppression of subretinal neovascularization in rho/VEGF mice but showed no difference in ischemia-induced retinal neovascularization compared with wild-type mice. These data indicate that NO is an important stimulator of choroidal neovascularization and that reduction of NO by pharmacologic or genetic means is a good treatment strategy. However, the situation is more complex for ischemia-induced retinal neovascularization for which NO produced in endothelial cells by eNOS is stimulatory, but NO produced in other retinal cells by iNOS and/or nNOS is inhibitory. Selective inhibitors of eNOS may be needed for treatment of retinal neovascularization.

Human endothelial nitric oxide synthase gene delivery promotes angiogenesis in a rat model of hindlimb ischemia

OBJECTIVE

Endothelium-derived NO has been shown to mediate the mitogenic effect of vascular endothelial growth factor on cultured microvascular endothelium. To evaluate the role of endothelial NO synthase (eNOS) in angiogenesis in the ischemic hindlimb, we engineered an adenovirus containing human eNOS cDNA.

METHODS AND RESULTS

After gene transfer, expression of eNOS in cultured cells was detected by increased intracellular cGMP and nitrate/nitrite levels and NO synthase activity. Adenovirus containing either the eNOS or luciferase gene was injected into the adductor muscle of rat hindlimbs immediately after femoral artery removal. Human eNOS protein was detected throughout the course of the experiment by immunostaining. Significant increases in blood perfusion were monitored by laser Doppler imaging from 2 to 4 weeks after gene delivery in the ischemic hindlimb of rats receiving eNOS compared with control rats receiving the reporter gene. An increase in regional blood flow was also detected after eNOS gene transfer by a fluorescent microsphere assay. eNOS gene delivery in the ischemic hindlimb resulted in significant increases in intracellular cGMP levels and in capillary density identified by anti-CD-31 immunostaining. Angiogenesis was further confirmed in mice after eNOS gene transfer by increased hemoglobin content in Matrigel implants.

CONCLUSIONS

Taken together, these results indicate that eNOS enhances angiogenesis and raises the potential of eNOS gene transfer for modulation of vascular insufficiency.

Angiostatin inhibits coronary angiogenesis during impaired production of nitric oxide

BACKGROUND

The in vivo mechanism by which inhibition of NO synthase impairs ischemia-induced coronary vascular growth is unknown. We hypothesized that production of the growth inhibitor angiostatin increases during decreased NO production, blunting angiogenesis and collateral growth.

METHODS AND RESULTS

Measurements were made in myocardial tissue or interstitial fluid (MIF) from dogs undergoing repetitive coronary occlusions under control conditions or during antagonism of NO synthase (N(G)-nitro-L-arginine methyl ester [L-NAME]) for 7, 14, or 21 days. A sham group was instrumented identically but received no occlusions. In controls, capillary density in the ischemic zone increased initially but returned to baseline at the later times. In the L-NAME group, capillary density was lower at 7 days compared with that of controls. MIF from control dogs induced in vitro endothelial tube formation and cell proliferation, significantly greater than that from the L-NAME group. MIF from shams did not stimulate tube formation. In controls or shams, tube formation or cell proliferation did not change after administration of antiangiostatin, but this antibody restored the responses to control levels in the L-NAME group. Angiostatin expression in MIF was increased in the L-NAME group compared with controls and shams. The activities of tissue matrix metalloproteinases (MMPs) MMP-2 and MMP-9, which generate angiostatin, were increased in the L-NAME group.

CONCLUSIONS

Inhibition of NO synthase increased expression of angiostatin and activities of MMP-2 and MMP-9. Our findings indicate that angiostatin inhibits coronary angiogenesis during compromised NO production and may underscore the impairment of coronary angiogenesis during endothelial dysfunction.

Nitric oxide is proangiogenic in the retina and choroid

Nitric oxide (NO) has been shown to have proangiogenic or antiangiogenic effects depending upon the setting. In this study, we used mice with targeted deletion of one of the three isoforms of nitric oxide synthase (NOS) to investigate the effects of NO in ocular neovascularization. In transgenic mice with increased expression of vascular endothelial growth factor (VEGF) in photoreceptors, deficiency of any of the three isoforms caused a significant decrease in subretinal neovascularization, but no alteration of VEGF expression. In mice with laser-induced rupture of Bruch's membrane, deficiency of inducible NOS (iNOS) or neuronal NOS (nNOS), but not endothelial NOS (eNOS), caused a significant decrease in choroidal neovascularization. In mice with oxygen-induced ischemic retinopathy, deficiency of eNOS, but not iNOS or nNOS caused a significant decrease in retinal neovascularization and decreased expression of VEGF. These data suggest that NO contributes to both retinal and choroidal neovascularization and that different isoforms of NOS are involved in different settings and different disease processes. A broad spectrum NOS inhibitor may have therapeutic potential for treatment of both retinal and choroidal neovascularization.

Synthesis of 1,25-dihydroxyvitamin D(3) by human endothelial cells is regulated by inflammatory cytokines: a novel autocrine determinant of vascular cell adhesion

In addition to its calciotropic function, the secosteroid 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) has potent nonclassical effects. In particular, local production of 1,25D(3) catalyzed by the enzyme 1alpha-hydroxylase (1alpha-OHase) may act as an autocrine/paracrine immunomodulatory mechanism. To investigate the significance of this in vascular tissue the expression and function of 1alpha-OHase in human endothelial cells was characterized. Immunohistochemical and in situ hybridization analyses show, for the first time, the presence of 1alpha-OHase mRNA and protein in endothelial cells from human renal arteries as well as postcapillary venules from lymphoid tissue. Reverse transcription-PCR and Western blot analyses confirmed the presence of 1alpha-OHase in primary cultures of human umbilical vein endothelial cells (HUVEC). Enzyme activity in HUVEC (318 +/- 56 fmoles 1,25(OH)(2)D(3)/hr/mg protein) increased after treatment with tumor necrosis factor-alpha (1054 +/- 166, P < 0.01), lipopolysaccharide (1381 +/- 88, P < 0.01), or forskolin (554 +/- 56, P < 0.05). Functional studies showed that exogenously added 1,25(OH)(2)D(3) or its precursor, 25-hydroxyvitamin D(3) (25(OH)D(3)), significantly decreased HUVEC proliferation after 72 h of treatment (33% and 11%, respectively). In addition, after 24 h treatment, both 1,25(OH)(2)D(3) and 25(OH)D(3) increased the adhesion of monocytic U937 cells to HUVEC (159% and 153%, respectively). These data indicate that human endothelia are able to produce active vitamin D. The rapid induction of endothelial 1alpha-OHase activity by inflammatory cytokines suggests a novel autocrine/paracrine role for the enzyme, possibly as a modulator of endothelial cell adhesion.

Localization of nitric oxide synthase in saphenous vein grafts harvested with a novel "no-touch" technique: potential role of nitric oxide contribution to improved early graft patency rates

OBJECTIVE

The use of the saphenous vein in coronary artery bypass graft surgery is associated with high 1-year occlusion rates of as much as 30%. A new "no-touch" technique of saphenous vein harvesting in which the vein is harvested with a pedicle of surrounding tissue and not distended may result in improved early patency rates. We hypothesize that nitric oxide synthase is better preserved with the no-touch technique, and the aim of this study was the investigation of whether nitric oxide synthase distribution and quantity in saphenous veins harvested with the no-touch technique differ from those veins harvested with the conventional technique. The separate contribution of perivascular tissue removal and distension to alterations in nitric oxide synthase was also studied.

METHODS

Segments of 10 saphenous veins were harvested from 10 patients who underwent coronary artery bypass grafting surgery with the no-touch and conventional techniques. Samples were also taken from segments that were stripped of surrounding tissue but not distended. Nitric oxide synthase distribution was studied with reduced nicotinamide adenine dinucleotide phosphate--diaphorase histochemistry, and staining was quantified with image analysis. Immunohistochemistry was used for the identification of specific nitric oxide synthase isoforms, and immunomarkers were used for the identification of associated cell types.

RESULTS

Nitric oxide synthase content was higher in no-touch vessels as compared with conventionally harvested vessels (35.5%; P <.05, with analysis of variance). This content was associated with endothelial nitric oxide synthase on the lumen while all three isoforms were present in the media. In the intact adventitia of no-touch vessels, all three isoforms of nitric oxide synthase were also present, associated with microvessels and perivascular nerves. Perivascular tissue stripping and venous distension both contribute to the reduced nitric oxide synthase in conventionally harvested veins.

CONCLUSION

The new no-touch technique of saphenous vein harvesting preserves nitric oxide synthase, which suggests that improved nitric oxide availability may be an important mechanism in the success of this technique.

Involvement of endothelial nitric oxide in sphingosine-1-phosphate-induced angiogenesis

Nitric oxide (NO) has been implicated as a critical signaling molecule of angiogenesis. Recently, sphingosine-1-phosphate (S1P) has emerged as a mediator of angiogenesis, and S1P-induced NO synthesis in endothelial cells (ECs) has been reported. To analyze the signaling pathways involved in S1P-induced angiogenesis and clarify the role of NO in this process, we performed in vivo and in vitro angiogenesis assays. S1P activated the phosphatidylinositol-3-kinase (PI3K)/Akt/endothelial NO synthase (eNOS) pathway in ECs, since S1P-stimulated eNOS phosphorylation and NO production were blocked by inhibition of activities of PI3K and Akt. S1P increased capillary ingrowth into subcutaneously implanted Matrigel plugs in mice, and the effect of S1P was significantly reduced in mice that received N(G)-nitro- L-arginine methyl ester (L-NAME), an inhibitor of NOS. S1P stimulated EC migration and tube formation on Matrigel, which processes were significantly decreased by inhibition of activities of PI3K, Akt, or eNOS, whereas treatment with LY294002, a PI3K inhibitor, but not L-NAME, inhibited EC viability and proliferation. Thus, our results demonstrate the crucial role of NO in S1P-induced angiogenesis in vivo and in vitro and suggest the divergent roles of NO in the S1P-induced angiogenic response.

Neuron-glia communication via nitric oxide is essential in establishing antennal-lobe structure in Manduca sexta

Nitric oxide synthase recently has been shown to be present in olfactory receptor cells throughout development of the adult antennal (olfactory) lobe of the brain of the moth Manduca sexta. Here, we investigate the possible involvement of nitric oxide (NO) in antennal-lobe morphogenesis. Inhibition of NO signaling with a NO synthase inhibitor or a NO scavenger early in development results in abnormal antennal lobes in which neuropil-associated glia fail to migrate. A more subtle effect is seen in the arborization of dendrites of a serotonin-immunoreactive neuron, which grow beyond their normal range. The effects of NO signaling in these types of cells do not appear to be mediated by activation of soluble guanylyl cyclase to produce cGMP, as these cells do not exhibit cGMP immunoreactivity following NO stimulation and are not affected by infusion of a soluble guanylyl cyclase inhibitor. Treatment with Novobiocin, which blocks ADP-ribosylation of proteins, results in a phenotype similar to those seen with blockade of NO signaling. Thus, axons of olfactory receptor cells appear to trigger glial cell migration and limit arborization of serotonin-immunoreactive neurons via NO signaling. The NO effect may be mediated in part by ADP-ribosylation of target cell proteins.