Production of angiogenic activity by human monocytes requires an L-arginine/nitric oxide-synthase-dependent effector mechanism

Nitric oxide and wound repair

NO produced by both iNOS and eNOS plays many important roles in wound healing, from the inflammatory phase through to scar remodeling. NO has cytostatic, chemotactic, and vasodilatory effects during early wound repair, regulates proliferation and differentiation of several cell types, modulates collagen deposition and angiogenesis, and affects wound contraction. The data accumulated thus far indicates that the timing, level, and site of NO production are highly coordinated in normal wound repair. Defining states resulting from either inadequate substrate or depressed enzyme expression appear to contribute to impaired wound repair; however, NO represents only one factor in the complex process of wound healing. Approaches to improve NO availability may be of therapeutic value.

NaF induces early differentiation of murine bone marrow cells along the granulocytic pathway but not the monocytic or preosteoclastic pathway in vitro

The stimulatory effects of sodium fluoride (NaF) on bone formation have been explained solely by its activation of osteoblasts. However, whether and how NaF acts on the osteoclast lineage is poorly understood. We previously found that NaF differentiates HL-60 cells to granulocytic cells. To further test this action, we have employed here primary cultures of progenitor cells derived from murine bone marrow. NaF at subtoxic concentrations (<0.5 mM) significantly up-regulated activities of several intracellular enzymes (lactate dehydrogenase, beta-glucuronidase, acid phosphatase), cellular reduction of nitroblue tetrazolium, and nitric oxide (NO) production; which are all accepted as general differentiation markers. NaF (<0.5 mM) also up-regulated granulocyte-specific markers (chloroacetate esterase, cell surface antigens [Mac-1, Gr-1]) but not any of the monocyte-specific markers (nonspecific esterase, cell surface antigens [F4/80, MOMA-2]). Although other general differentiation markers (phagocytosis, adhesion, appearance, nuclear:cytoplasmic ratio) were not appreciably influenced by NaF, essentially in support of our previous data from HL-60 cells, the present findings suggest that NaF induces early differentiation of bone marrow hemopoietic progenitor cells along the granulocytic pathway but not the monocytic pathway that is linked to osteoclast formation. Therefore, in addition to its potent stimulatory effects on osteoblastic bone formation, NaF applied to patients with osteoporosis could be expected to indirectly reduce osteoclastic bone resorption.

Inhibition of inducible nitric oxide synthase results in reductions in wound vascular endothelial growth factor expression, granulation tissue formation, and local perfusion

BACKGROUND

Wound repair results from a series of highly orchestrated cellular and biochemical events, including increased synthesis of the bioregulatory molecule nitric oxide (NO). The goal of this work was to test the functional role of NO in promotion of vascular endothelial growth factor (VEGF) production and the vigorous granulation tissue formation characteristic of this wound model.

METHODS

A ventral hernia, surgically created in the abdominal walls of 12 swine, was repaired with silicone sheeting and skin closure. An osmotic infusion pump, inserted in a remote subcutaneous pocket, delivered saline solution (n = 6) or the selective inducible NO synthase inhibitor N(6) (iminoethyl)-L-lysine (L-NIL; n = 6) into the wound environment. Granulation tissue thickness was determined with ultrasonography, and local wound perfusion was measured with laser Doppler analysis for 2 weeks. Fluid was aspirated serially from the wound compartment for measurement of nitrite/nitrate, VEGF, and transforming growth factor-beta(1)concentrations. On day 14, the animals were killed and the abdominal wall was harvested for immunohistochemical and molecular analysis.

RESULTS

In animals that received saline solution, a nearly linear 4-fold increase in granulation tissue thickness was measured during the 14-day interval. In contrast, in animals that received L-NIL, day 14 granulation tissue thickness was essentially unchanged from the day 2 values of saline solution-treated animals. Moreover, in the L-NIL animals, ultrasonography was unable to resolve the angiogenic zone typical of controls, and correspondingly, wound vessel count and vascular surface area estimates derived from image analysis of histologic sections were 2-fold to 3-fold lower in the L-NIL animals compared with controls. Reductions in basal (2-fold) and heat-provoked (2.5-fold) wound perfusion were noted in L-NIL animals. Wound fluid nitrite/nitrate and VEGF levels were strikingly (4-fold and 5-fold, respectively) reduced in L-NIL animals on days 9 to 14. Immunochemistry results showed reduced VEGF protein content in granulation tissue and keratinocytes within the hyperproliferative epithelium at wound edge. Finally, transforming growth factor-beta(1)levels were unaffected by L-NIL treatment.

CONCLUSION

VEGF production in granulation tissue is dependent on the presence of functionally active inducible NO synthase and hence, the production of NO. NO and VEGF are therefore defined as key regulators of granulation tissue formation.

Specific expression of inducible nitric oxide synthase in the synovium of the diseased temporomandibular joint

OBJECTIVE

The expression of inducible nitric oxide synthase (iNOS) in temporomandibular joint (TMJ) specimens obtained arthroscopically from diseased TMJs was investigated by using immunohistochemistry and compared with clinical, arthroscopic, and histologic findings.

STUDY DESIGN

Synovial biopsies were obtained arthroscopically from 18 TMJs in 15 patients with symptomatic internal derangement (ID) or osteoarthritis (OA). We also obtained arthroscopic biopsies from 8 control TMJs (3 with habitual luxation of the mandible, one with ID with clicking, and 4 with mandibular condyle fractures). The expression of iNOS was examined by immunohistochemistry and was compared with clinical, arthroscopic, and histologic findings.

RESULTS

Definite or intense iNOS immunoreactivity was observed in both the synovial lining cells and the endothelial cells of TMJs with symptomatic ID or OA. Weaker immunoreactivity was present in synovial fibroblasts. In contrast, in TMJs without synovitis (eg, those with habitual luxation of the mandible) the expression of iNOS was weak or marginal. The expression of iNOS correlated significantly with arthroscopic evidence of synovitis (r = 0.406, P <.05) but not with cartilaginous degeneration (P >.05). The expression of iNOS also correlated with the histologic grade of the synovial lining cell layers (r = 0.530, P <.05). However, in patients with ID or OA of the TMJ, there was no statistically significant correlation between the intensity of iNOS immunoreactivity and clinical, arthroscopic, or histologic findings (P >.05).

CONCLUSION

These data clearly suggest that nitric oxide is locally produced in the synovial lining of the TMJ in ID and OA.

Redox signaling in vascular angiogenesis

Angiogenesis is thought to be regulated by several growth factors (EGF, TGF-alpha, beta-FGF, VEGF). Induction of these angiogenic factors is triggered by various stresses. For instance, tissue hypoxia exerts its pro-angiogenic action through various angiogenic factors, the most notable being vascular endothelial growth factor, which has been mainly associated with initiating the process of angiogenesis through the recruitment and proliferation of endothelial cells. Recently, reactive oxygen species (ROS) have been found to stimulate angiogenic response in the ischemic reperfused hearts. Short exposure to hypoxia/reoxygenation, either directly or indirectly, produces ROS that induce oxidative stress which is associated with angiogenesis or neovascularization. ROS can cause tissue injury in one hand and promote tissue repair in another hand by promoting angiogenesis. It thus appears that after causing injury to the cells, ROS promptly initiate the tissue repair process by triggering angiogenic response.

Redox signaling of angiogenesis

Reactive oxygen species (ROS) play a crucial role in vascular angiogenesis. Both in vitro and in vivo studies indicate that angiogenic response in vascular tissue is triggered by ROS signaling in a highly coordinated manner. It appears that massive amounts of ROS produced during ischemia and reperfusion in the vascular tissue, especially in heart, cause significant injury to the cardiomyocyte and endothelial cells. However, during the reperfusion, the same ROS potentiates a repair process and triggers a signal transduction cascade leading to angiogenesis. Although several other factors are likely to be involved for such angiogenic response, ROS certainly plays a crucial role as evident from its direct role as mediator of angiogenesis and inhibition of angiogenesis with free radical scavengers and/or antioxidants. Angiogenesis is regulated by redox-sensing transcription factors such as nuclear factor-kappaB, and oxidants such as hydrogen peroxide and free radicals, such as nitric oxide may function as second messengers in this highly coordinated process. Furthermore, expression of many angiogenic genes including those for vascular endothelial growth factor, fibroblast growth factor, platelet-derived growth factor, and receptors such as Flt-1, Flk-1, Ang-1, and Ang-2 are likely to be regulated by redox signaling. It is tempting to speculate that the angiogenic response is under the autocrine and/or paracrine control of one or more cytokines, which in turn is redox-regulated. Through angiogenesis, ROS appear to pave the way of repairing the vascular tissues that have been damaged during ischemia and reperfusion.

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.

Nitric oxide and wound repair: role of cytokines?

Wound healing involves platelets, inflammatory cells, fibroblasts, and epithelial cells. All of these cell types are capable of producing nitric oxide (NO), either constitutively or in response to inflammatory cytokines, through the activity of nitric oxide synthases (NOSs): eNOS (NOS3; endothelial NOS) and iNOS (NOS2; inducible NOS), respectively. Indeed, pharmacological inhibition or gene deletion of these enzymes impairs wound healing. The wound healing mechanisms that are triggered by NO appear to be diverse, involving inflammation, angiogenesis, and cell proliferation. All of these processes are controlled by defined cytokine cascades; in many cases, NO appears to modulate these cytokines. In this review, we summarize the history and present state of research on the role of NO in wound healing within the framework of modulation of cytokines.

Nitric oxide and vascular endothelial growth factor concentrations are increased but not related in vitreous fluid of patients with proliferative diabetic retinopathy

AIMS

Several reports have implicated nitric oxide (NO) in the angiogenic process. The assessment of NO stable end products, nitrite and nitrate (NOx), is commonly used as a measure of NO production in biological fluids. The aims of the study were to investigate NOx concentrations in the vitreous fluid of patients with proliferative diabetic retinopathy (PDR) and to evaluate the relationship between NOx and vascular endothelial growth factor (VEGF).

PATIENTS AND METHODS

Serum and vitreous fluid samples were obtained simultaneously at the time of vitreoretinal surgery from 23 patients with PDR, and 17 control non-diabetic patients with non-proliferative ocular disease. NOx was determined by using the Griess reaction and VEGF levels were assessed by ELISA.

RESULTS

The intravitreous concentration of NOx was significantly elevated in patients with PDR in comparison with the control group (31.6 +/- 2.96 micromol/l vs. 18 +/- 2.46 micromol/l; P = 0.01). However, we did not detect any differences between NOx serum concentrations. We observed a correlation between serum and vitreous levels of NOx in diabetic patients (r = 0.79; P < 0.001), but not in the control group. Intravitreous levels of VEGF in patients with PDR were higher than those obtained in serum (1.42 ng/ml (0.12-7.62) vs. 0.12 ng/ml (0.03-0.42); P < 0.01). Vitreal levels of VEGF were strikingly higher in patients with PDR than in the control subjects (1.42 ng/ml (0.12-7.62) vs. 0.009 ng/ml (0.009-0.04); P < 0.001). No correlation between vitreal concentrations of NOx and VEGF was observed, either in diabetic patients or in the control group.

CONCLUSIONS

NOx and VEGF are increased but not related in the vitreous fluid of diabetic patients with PDR. Our results suggest that serum diffusion could play a significant role in explaining the increase of NOx. By contrast, intraocular production seems to be the main factor responsible for the intravitreous enhancement of VEGF.

Ultrasound stimulates nitric oxide and prostaglandin E2 production by human osteoblasts

We have previously shown that the therapeutic range of ultrasound heals osteoradionecrotic bone and induces bone formation in vitro. It is well established that nitric oxide (NO) and prostaglandins are crucial early mediators in mechanically induced bone formation. The therapeutic range of ultrasound may act in the same way; therefore, we have investigated the effect of the therapeutic range of ultrasound on NO induction and prostaglandin E(2) (PGE(2)) production in vitro. Two ultrasound machines were evaluated, "traditional" (1 MHz, pulsed 1:4, tested at four intensities) and a "long-wave" (45 kHz, continuous, also tested at four intensities) devices. Ultrasound was applied to human mandibular osteoblasts for 5 min, and incubated at 37 degrees C for up to 24 h. The control group (sham insonated) was treated in the same way. NO was determined by measuring the nitrite concentration in the culture media colorimetrically, and PGE(2) was assayed by radioimmunoassay. Ultrasound produced a significant increase in both induced nitrite and PGE(2) production. The NO synthesis appeared to be via inducible NO synthase (iNOS) on the basis of the time course and levels of nitrite obtained, although the inhibition of other NOS isoforms by aminoguanidine cannot be excluded. PGE(2) synthesis appeared to be via COX-2. With the 45 kHz machine, a significant increase in NO was achieved at three intensities, 5, 30, and 50 mW/cm(2). The 1 MHz machine stimulated the synthesis of both NO and PGE(2), but was significant at only one dose (0.1 W/cm(2(SAPA))). There was no difference between the two machines with regard to PGE(2) synthesis. The time-course experiment revealed peak production to be 12-18 h for both NO and PGE(2). The therapeutic range of ultrasound stimulates both NO and PGE(2) synthesis by human osteoblasts, and the 45 kHz machine appeared to be more effective than the traditional short-wave length. These results may reflect the healing effect of ultrasound on fractures and osteoradionecrosis.

Endothelial dysfunction in ischemic acute renal failure: rescue by transplanted endothelial cells

There is accumulating circumstantial evidence suggesting that endothelial cell dysfunction contributes to the "no-reflow" phenomenon in postischemic kidneys. Here, we demonstrated the vulnerability of in vitro, ex vivo, and in vivo endothelial cells exposed to pathophysiologically relevant insults, such as oxidative and nitrosative stress or ischemia. All of these stimuli compromised the integrity of the endothelial lining. Next, we performed minimally invasive intravital microscopy of blood flow in peritubular capillaries, which provided direct evidence of the existence of the no-reflow phenomenon, attributable, at least in part, to endothelial injury. In an attempt to ameliorate the hemodynamic consequences of lost endothelial integrity, we transplanted endothelial cells or surrogate cells expressing endothelial nitric oxide synthase into rats subjected to renal artery clamping. Implantation of endothelial cells or their surrogates expressing functional endothelial nitric oxide synthase in the renal microvasculature resulted in a dramatic functional protection of ischemic kidneys. These observations strongly suggest that endothelial cell dysfunction is the primary cause of the no-reflow phenomenon, which, when ameliorated, results in prevention of renal injury seen in acute renal failure.

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.

Cutaneous microcirculation in the neuropathic diabetic foot improves significantly but not completely after successful lower extremity revascularization

OBJECTIVE

The purpose of this study was the examination of the effect of successful large vessel revascularization on the microcirculation of the neuroischemic diabetic foot.

RESEARCH DESIGN AND METHODS

We measured the cutaneous microvascular reactivity in the foot in 13 patients with diabetes with peripheral arterial disease and neuropathy (group DI) before and 4 to 6 weeks after successful lower extremity arterial revascularization. We also compared them with age-matched and sex-matched groups of 15 patients with diabetes and neuropathy, seven patients without neuropathy, and 12 healthy patients for control. We used single-point and laser Doppler scan imaging for the measurement of the foot skin vasodilatation in response to heating to 44 degrees C and to iontophoresis of 1% acetylcholine (endothelial-dependent response) and 1% sodium nitroprusside (endothelial-independent response).

RESULTS

The group DI response to heat increased from 289% +/- 90% before surgery (percent increase over baseline measured in volts) to 427% +/- 61% (P <.05) after surgery but was still comparable with the response of the patients with diabetes and neuropathy (318% +/- 51%) and lower than the responses of the patients without neuropathy (766% +/- 220%) and the healthy patients for control (891% +/- 121%; P <.0001). The group DI acetylcholine response also improved from 6% +/- 4% before surgery to 26% +/- 8% after surgery (P <.05) and was similar to the responses of patients with diabetes and neuropathy (18% +/- 3%) and patients without neuropathy (38% +/- 8%) but still lower when compared with the response of the patients for control (48% +/- 9%; P <.001). The sodium nitroprusside response for group DI improved from 10% +/- 4% to 29% +/- 9% (P <.05) and was similar to the responses of the neuropathic (25% +/- 9%), nonneuropathic (32% plus minus 6%), and control (40% +/- 5%) groups. The group DI neurovascular response, which depends on the healthy function of the C-fiber nociceptors, was similar at baseline (5% +/- 9%) and after surgery (14% +/- %10) and in the neuropathic group (33% +/- 21%), but it was dramatically reduced when compared with the nonneuropathic (110% +/- 40%) and control (198% +/- 54%) groups (P <.001).

CONCLUSION

Impaired vasodilation in the diabetic neuropathic lower extremity leads to functional ischemia, which improves considerably but is not completely corrected with successful bypass grafting surgery. Therefore, patients with diabetes and neuropathy may still be at high risk for the development of foot ulceration or the failure to have an existing ulcer heal despite adequate correction of large vessel blood flow.

Chronic blockade of endothelin receptors improves ischemia-induced angiogenesis in rat hindlimbs through activation of vascular endothelial growth factor-no pathway

This study investigated in vivo the putative angiogenic role of endothelin (ET)-1 in a model of ischemia-induced angiogenesis. Ischemia was produced by unilateral femoral artery occlusion in Wistar rats submitted to either chronic ET-1 infusion (2 nmol. kg(-1). min(-1)) or to a dual ET(A)/ET(B) receptor antagonist (bosentan, 100 mg. kg(-1). d(-1)) for 3 and 28 days. Arterial density was evaluated by microangiography and measurement of capillary and arteriolar density in hindlimb muscles. ET-1 infusion had no effect on ischemia-induced angiogenesis and was associated with a slight decrease in vascular endothelial growth factor (VEGF) content measured by Western blot analysis. Conversely, bosentan induced a marked increase in vessel density at 3 and 28 days (1.4-fold and 1.7-fold, respectively, compared with no treatment; P<0.05), which was associated with an increase in VEGF and endothelial NO synthase levels in ischemic legs (by 31+/-8% and 45+/-23%, respectively, at 3 days and by 65+/-13% and 55+/-15%, respectively, at 28 days; P<0.05 versus nontreated rats). At day 28, the proangiogenic effect of bosentan was abolished when NO synthesis inhibitor N(G)-nitro-L-arginine methyl ester (10 mg. kg(-1). d(-1)) or VEGF-neutralizing antibody (2.5 micro/kg twice a week) were coadministered with bosentan. Those results provide the first evidence of an early and sustained proangiogenic effect of endothelin antagonism associated with an upregulation of VEGF and endothelial NO synthase in vivo.

Mechanism of temporal gradients in shear-induced ERK1/2 activation and proliferation in endothelial cells

The aim of the current study was to investigate the intracellular signaling cascade that leads to temporal gradients in shear (TGS)-induced endothelial cell proliferation, with a focus on the involvement of extracellular signal-regulated kinases 1 and 2 (ERK1/2). With the use of well-defined pulsatile, impulse, step, and ramp laminar flow profiles, we found that TGS (impulse flow and pulsatile flow) induced an enhanced and sustained (>30 min) phosphorylation of ERK1/2 relative to step flow (which contains a step increase in shear followed by steady shear), whereas steady shear (ramp flow) alone downregulated activated ERK1/2. Nitric oxide (NO) was found to mediate both the stimulatory effect of TGS and the inhibitory effect of steady shear on endothelial ERK1/2 phosphorylation. Reactive oxygen species (ROS) were also demonstrated to be associated with TGS-induced ERK1/2 phosphorylation. Both G(q/11) and G(i3) were necessary for the activation of ERK1/2 by TGS. Finally, the TGS-induced endothelial proliferative response was abolished by ERK1/2 inhibition. Our study demonstrated the essential role of G proteins, NO, and ROS in TGS-dependent ERK1/2 activation and proliferative response in vascular endothelial cells.

In vivo angiogenesis in normal and portal hypertensive rats: role of basic fibroblast growth factor and nitric oxide

BACKGROUND

Angiogenesis plays a pivotal role in many processes. Here, we studied whether angiogenesis to basic fibroblast growth factor (bFGF) in normal and portal hypertensive rats requires nitric oxide (NO).

METHODS

To measure angiogenesis in vivo, two Teflon rings filled with collagen I (Vitrogen 100) were fixed in the mesenteric cavity at day 0, with one supplemented with bFGF (100 ng). Portal hypertension was induced by partial portal vein ligation (PVL). Sham-operated rats served as controls (CON). The role of NO was tested by adding the NO formation antagonist N(omega)-nitro-L-arginine (NNA; 3.3 mg/kg per day) to the drinking water. After 16 days, rings were explanted and embedded, and vessels were morphometrically counted.

RESULTS

bFGF significantly stimulated vessel formation per implant in CON rats (from 624 +/- 97 without stimulation to 1123 +/- 171, n = 11, P < 0.01), but not in PVL rats (from 1106 +/- 174 without stimulation to 1046 +/- 202, n = 9). Without stimulation, numbers of ingrown vessels were significantly (P < 0.05) higher in PVL compared to CON rats. NNA substantially inhibited angiogenesis in both groups (P < 0.01). Vessel numbers were 202 +/- 124 for PVL (n = 5) and 197 +/- 14 for CON (n = 5) animals. bFGF did not reverse angiogenesis prevented by NNA (373 +/- 98 for PVL, 265 +/- 26 for CON, n = 5 per group, NS).

CONCLUSIONS

NO formation inhibition diminishes both unstimulated and bFGF-stimulated angiogenesis in CON rats. Moreover, bFGF cannot rescue NNA-inhibited angiogenesis in PVL rats.

Glucose scavenging of nitric oxide

Endothelial dysfunction accompanies suboptimal glucose control in patients with diabetes mellitus. A hallmark of endothelial dysfunction is a deficiency in production or bioavailability of vascular nitric oxide (NO). Here we demonstrate that acute exposure of human endothelial cells to glucose, at levels found in plasma of diabetic patients, results in a significant blunting of NO responses to the endothelial nitric oxide synthase (eNOS) agonists bradykinin and A-23187. Monitoring of NO generation by purified recombinant bovine eNOS in vitro, using amperometric electrochemical detection and an NO-selective porphyrinic microelectrode, showed that glucose causes a progressive and concentration-dependent attenuation of detectable NO. Addition of glucose to pure NO solutions similarly elicited a sharp decrease in NO concentration, indicating that glucose promotes NO loss. Electrospray ionization-tandem mass spectrometry, using negative ion monitoring, directly demonstrated the occurrence of a covalent reaction involving unitary addition of NO (or a derived species) to glucose. Collectively, our findings reveal that hyperglycemia promotes the chemical inactivation of NO; this glucose-mediated NO loss may directly contribute to hypertension and endothelial dysfunction in diabetic patients.

Workshop: endothelial cell dysfunction leading to diabetic nephropathy : focus on nitric oxide

Clinical manifestations of diabetic nephropathy are an expression of diabetic microangiopathy. This review revisits the previously proposed Steno hypothesis and advances our hypothesis that development of endothelial cell dysfunction represents a common pathophysiological pathway of diabetic complications. Specifically, the ability of glucose to scavenge nitric oxide is proposed as the initiation phase of endothelial dysfunction. Gradual accumulation of advanced glycated end products and induction of plasminogen activator inhibitor-1, resulting in the decreased expression of endothelial nitric oxide synthase and reduced generation of nitric oxide, are proposed to be pathophysiologically critical for the maintenance phase of endothelial dysfunction. The proposed conceptual shift toward the role of endothelial dysfunction in diabetic complications may provide new strategies for their prevention.

Nitric oxide: a review for veterinary surgeons

Nitric oxide (NO) is an endogenous gas that serves as a biologic messenger in many physiologic processes including neurotransmission, blood-pressure control, the immune system's ability to kill tumor cells, and wound healing. NO is produced after oxidation of L-arginine by a family of nitric oxide synthase (NOS) enzymes. Two of the NOS enzymes are present continuously and are thereby termed constitutive NOS. One of the enzymes, inducible NOS, is not typically expressed in resting cells and is induced by various substances including endotoxin, some cytokines, and microbial products. Thus, NO often has paradoxical activities. When NO is over- or underproduced, it can result in potentiation of disease states with disastrous results. This review discusses the biochemistry of NO, its functions in normal and disease states, and therapy for modulating NO production in disease states.

Temporal expression of nitric oxide synthase isoforms in healing Achilles tendon

We investigated the temporal expressions of the three nitric oxide synthase (NOS) isoforms by semi-quantitative polymerase chain reaction (PCR) assays and by immunoblot analysis, following Achilles tendon transection in rats. Four days after injury, there were increases in the steady-state levels of mRNA for all three NOS isoforms, with peaks for the inducible isoform (iNOS) (23-fold increase) at day 4, the endothelial isoform (eNOS) (24-fold increase) at day 7 and the neuronal isoform (bNOS) (seven-fold increase) at day 21. The temporal expression of NOS isoforms at a protein level was consistent with the results at the mRNA level. We have previously shown a five-fold increase in the NOS activity, as detected by 3H-arginine to 3H-citrulline conversion, at day 7 postinjury. These findings indicate that all three NOS isoforms are expressed during tendon healing with differential expression patterns during the various phases of tendon healing. These findings may prove clinically relevant with respect to strategies for regulating tendon healing.

COX-2, NO, and cartilage damage and repair

The production of nitric oxide (NO) and prostaglandin E2 (PGE(2)) is increased in human osteoarthritis-affected cartilage. These and other inflammatory mediators are spontaneously released by OA cartilage explants ex vivo. The excessive production of nitric oxide inhibits matrix synthesis, and promotes its degradation. Furthermore, by reacting with oxidants such as superoxide anion, nitric oxide promotes cellular injury, and renders the chondrocyte susceptible to cytokine-induced apoptosis. PGE(2) exerts both anabolic and catabolic effects on chondrocytes, depending on the microenvironment and physiological condition. Thus, NO and PGE(2), produced by activated chondrocytes in diseased cartilage, may modulate disease rogression in osteoarthritis, and should therefore be considered potential targets for therapeutic intervention

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

Nitric oxide (NO) has been implicated as a mediator of angiogenesis. However, its precise role in angiogenesis and its mechanism of action have not been established. We performed in vivo and in vitro angiogenesis assays using NO donor S-nitroso-N-acetylpenicillamine (SNAP) and NO synthase inhibitor N-iminoethyl-l-ornithine (L-NIO). SNAP significantly increased and L-NIO significantly suppressed capillary ingrowth into subcutaneously implanted Matrigel plugs in mice. For the in vitro angiogenesis assay, human umbilical vein endothelial cells (HUVECs) (4 x 10(4) cells/well) were treated with placebo, SNAP (100 microM), or L-NIO (100 microM) and cultured on Matrigel for 18 h. The typical capillary networks formed on Matrigel by HUVECs as a result of cell migration and differentiation were quantified by computer-assisted image analysis as a measure of angiogenesis. Treatment of HUVECs with SNAP significantly increased the capillary network area compared with control, 8701 +/- 693 vs 6258 +/- 622 area units (P < 0.05), whereas L-NIO significantly decreased the capillary area (4540 +/- 342, P < 0.05). Furthermore, we have shown with a blocking monoclonal antibody that formation of capillary networks on Matrigel is mediated by the functional expression of the alpha(v)beta(3) integrin, which plays a role in facilitating endothelial cell adhesion to basement membrane matrix and endothelial cell migration. After an 18-h culture, flow cytometry revealed that SNAP significantly upregulated and L-NIO significantly downregulated in a concentration-dependent manner alpha(v)beta(3) integrin expression on endothelial cells. In conclusion, NO induces angiogenesis in vivo and in vitro by promoting endothelial cell migration and differentiation into capillaries. One possible mechanism might involve the upregulation of alpha(v)beta(3) integrin on endothelial cells, a critical mediator of cell-matrix adhesion and migration.

Effects of homocysteine on endothelial nitric oxide production

Hyperhomocysteinemia (HHCy) is an independent and graded cardiovascular risk factor. HHCy is prevalent in patients with chronic renal failure, contributing to the increased mortality rate. Controversy exists as to the effects of HHCy on nitric oxide (NO) production: it has been shown that HHCy both increases and suppresses it. We addressed this problem by using amperometric electrochemical NO detection with a porphyrinic microelectrode to study responses of endothelial cells incubated with homocysteine (Hcy) to the stimulation with bradykinin, calcium ionophore, or L-arginine. Twenty-four-hour preincubation with Hcy (10, 20, and 50 microM) resulted in a gradual decline in responsiveness of endothelial cells to the above stimuli. Hcy did not affect the expression of endothelial nitric oxide synthase (eNOS), but it stimulated formation of superoxide anions, as judged by fluorescence of dichlorofluorescein, and peroxynitrite, as detected by using immunoprecipitation and immunoblotting of proteins modified by tyrosine nitration. Hcy did not directly affect the ability of recombinant eNOS to generate NO, but oxidation of sulfhydryl groups in eNOS reduced its NO-generating activity. Addition of 5-methyltetrahydrofolate restored NO responses to all agonists tested but affected neither the expression of the enzyme nor formation of nitrotyrosine-modified proteins. In addition, a scavenger of peroxynitrite or a cell-permeant superoxide dismutase mimetic reversed the Hcy-induced suppression of NO production by endothelial cells. In conclusion, electrochemical detection of NO release from cultured endothelial cells demonstrated that concentrations of Hcy >20 microM produce a significant indirect suppression of eNOS activity without any discernible effects on its expression. Folates, superoxide ions, and peroxynitrite scavengers restore the NO-generating activity to eNOS, collectively suggesting that cellular redox state plays an important role in HCy-suppressed NO-generating function of this enzyme.

Nitric oxide and angiogenesis

The steps required for new vessel growth are biologically complex and require coordinate regulation of contributing components, including modifications of cell--cell interactions, proliferation and migration of endothelial cells and matrix degradation. The observation that in vivo angiogenesis is accompanied by vasodilation, that many angiogenesis effectors possess vasodilating properties and that tumor vasculature is in a persistent state of vasodilation, support the existence of a molecular/biochemical link between vasodilation and angiogenesis. Several pieces of evidence converge in the indication of a role for nitric oxide (NO), the factor responsible for vasodilation, in physiological and pathological angiogenesis. Data originated in different labs indicate that NO can act both as an 'actor' of angiogenesis and as a 'director of angiogenesis', both functions being equally expressed during physiological and pathological processes. NO significantly contributes to the prosurvival/proangiogenic program of capillary endothelium by triggering and transducing cell growth and differentiation via endothelial-constitutive NO synthase (ec-NOS) activation, cyclic GMP (cGMP) elevation, mitogen activated kinase (MAPK) activation and fibroblast growth factor-2 (FGF-2) expression. Re-establishment of a balanced NO production in the central nervous system results in a reduction of cell damage during inflammatory and vascular diseases. Elevation of NOS activity in correlation with angiogenesis and tumor progression has been extensively reported in experimental and human tumors. In the brain, tumor expansion and edema formation are sensitive to NOS inhibition. On this basis, the nitric oxide pathway appears to be a promising target for consideration in pro- and anti-angiogenic therapeutic strategies. The use of NOS inhibitors seems appropriate to reduce edema, block angiogenesis and facilitate antitumor drug delivery.

Dimerization of major histocompatibility complex class I on the surface of THP-1 cells stimulates the expression of inducible nitric oxide synthase and subsequent nitric oxide release

We show that dimerization of major histocompatibility complex (MHC) class I on a human monocytic cell line, THP-1, induces nitric oxide (NO) synthesis. Cells cultured in the presence of a human MHC class I-specific monoclonal antibody produced significant amounts of NO after 72 hr. Reverse transcription-polymerase chain reaction and flow cytometry analysis revealed that the cells synthesized detectable levels of inducible NO synthase mRNA and protein. These effects were not seen after treatment with monovalent Fab fragments or Fc fragments of the same antibody, or after treatment with a control antibody. These data show a link between innate and acquired immune mechanisms mediated by NO and MHC class I.

Human endothelial cells express CCR2 and respond to MCP-1: direct role of MCP-1 in angiogenesis and tumor progression

Although several CXC chemokines have been shown to induce angiogenesis and play roles in tumor growth, to date, no member of the CC chemokine family has been reported to play a direct role in angiogenesis. Here we report that the CC chemokine, monocyte chemotactic protein 1 (MCP-1), induced chemotaxis of human endothelial cells at nanomolar concentrations. This chemotactic response was inhibited by a monoclonal antibody to MCP-1. MCP-1 also induced the formation of blood vessels in vivo as assessed by the chick chorioallantoic membrane and the matrigel plug assays. As expected, the angiogenic response induced by MCP-1 was accompanied by an inflammatory response. With the use of a rat aortic sprouting assay in the absence of leukocytic infiltrates, we ruled out the possibility that the angiogenic effect of MCP-1 depended on leukocyte products. Moreover, the direct effect of MCP-1 on angiogenesis was consistent with the expression of CCR2, the receptor for MCP-1, on endothelial cells. Assessment of supernatant from a human breast carcinoma cell line demonstrated the production of MCP-1. Treatment of immunodeficient mice bearing human breast carcinoma cells with a neutralizing antibody to MCP-1 resulted in significant increases in survival and inhibition of the growth of lung micrometastases. Taken together, our data indicate that MCP-1 can act as a direct mediator of angiogenesis. As a chemokine that is abundantly produced by some tumors, it can also directly contribute to tumor progression. Therefore, therapy employing antagonists of MCP-1 in combination with other inhibitors of angiogenesis may achieve more comprehensive inhibition of tumor growth.

Human endothelial cells express CCR2 and respond to MCP-1: direct role of MCP-1 in angiogenesis and tumor progression

Although several CXC chemokines have been shown to induce angiogenesis and play roles in tumor growth, to date, no member of the CC chemokine family has been reported to play a direct role in angiogenesis. Here we report that the CC chemokine, monocyte chemotactic protein 1 (MCP-1), induced chemotaxis of human endothelial cells at nanomolar concentrations. This chemotactic response was inhibited by a monoclonal antibody to MCP-1. MCP-1 also induced the formation of blood vessels in vivo as assessed by the chick chorioallantoic membrane and the matrigel plug assays. As expected, the angiogenic response induced by MCP-1 was accompanied by an inflammatory response. With the use of a rat aortic sprouting assay in the absence of leukocytic infiltrates, we ruled out the possibility that the angiogenic effect of MCP-1 depended on leukocyte products. Moreover, the direct effect of MCP-1 on angiogenesis was consistent with the expression of CCR2, the receptor for MCP-1, on endothelial cells. Assessment of supernatant from a human breast carcinoma cell line demonstrated the production of MCP-1. Treatment of immunodeficient mice bearing human breast carcinoma cells with a neutralizing antibody to MCP-1 resulted in significant increases in survival and inhibition of the growth of lung micrometastases. Taken together, our data indicate that MCP-1 can act as a direct mediator of angiogenesis. As a chemokine that is abundantly produced by some tumors, it can also directly contribute to tumor progression. Therefore, therapy employing antagonists of MCP-1 in combination with other inhibitors of angiogenesis may achieve more comprehensive inhibition of tumor growth.

Ley/H: an endothelial-selective, cytokine-inducible, angiogenic mediator

Endothelial cells (ECs) are key participants in angiogenic processes that characterize tumor growth, wound repair, and inflammatory diseases, such as human rheumatoid arthritis (RA). We and others have shown that EC molecules, such as soluble E-selectin, mediate angiogenesis. Here we describe an EC molecule, Lewisy-6/H-5-2 glycoconjugate (Ley/H), that shares some structural features with the soluble E-selectin ligand, sialyl Lewisx (sialyl Lex). One of the main previously recognized functions of Lewisy is as a blood group glycoconjugate. Here we show that Ley/H is rapidly cytokine inducible, up-regulated in RA synovial tissue, where it is cell-bound, and up-regulated in the soluble form in angiogenic RA compared with nonangiogenic osteoarthritic joint fluid. Soluble Ley/H also has a novel function, for it is a potent angiogenic mediator in both in vitro and in vivo bioassays. These results suggest a novel paradigm of soluble blood group Ags as mediators of angiogenic responses and suggest new targets for therapy of diseases, such as RA, that are characterized by persistent neovascularization.

Selective augmenting effects of nitric oxide on antigen-specific IgE response in mice

Here, we report the enhancing effects of nitric oxide (NO) on an IgE antibody response in mice. Anti-trinitrophenyl (TNP) IgE production induced in vitro in TNP keyhole limpet hemocyanin (KLH)-primed spleen cells was inhibited by approximately 70% when an NO synthase (NOS) inhibitor, L-N(G)-monomethyl-L-arginine, was added at 10(-7)-10(-6) M to the lymphocyte culture. On the other hand, addition of NO-generating agents to the culture resulted in a marked enhancement of the IgE production. In contrast, anti-TNP IgM and IgG1 responses were affected only marginally when the IgE production was either suppressed or augmented by these agents. NO did not directly augment IgE class switching in normal B cells stimulated with lipopolysaccharide and interleukin (IL)-4. NO-mediated augmentation of the IgE response is considered to be of a physiological significance because administration of aminoguanidine (AG), an inhibitor of inducible NOS, to immunized mice resulted in a preferential suppression of anti-TNP IgE production in vivo. This may be explained by the observation that AG-administration increased interferon-gamma expression without changing that of IL-4 in the immunized mice. Taken together, these observations suggest a pathophysiological role of NO in the development of IgE-mediated allergic diseases.

A pivotal role of nitric oxide in endothelial cell dysfunction

The functional role of the vascular endothelium is a subject of growing interest and appreciation. Some of the key functions of the endothelium are modulated by the activity and expression of endothelial nitric oxide synthase (eNOS), suggesting a role for this enzyme in endothelial dysfunction. Several well-known angiogenic stimulators exert their effect only in the presence of the functional eNOS. In this setting NO production is responsible for the scalar podokinetic cell motility, which is a prerequisite for the acquisition of vectorial movement when guidance cues are applied. The mode of this NO action appears to lie in the accelerated turnover of focal adhesions through the process of activation/inactivation of protein tyrosine phosphatases. Localization of eNOS to the caveolar domains, in the proximity of clustered beta1 integrins, provides an additional level of regulatory complexity through the modulation of caveolar dynamics and the state of caveolin oligomerization. Therefore, eNOS serves various important functions in the endothelium and is a putative target for therapeutic interventions.

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)

Impaired wound healing and angiogenesis in eNOS-deficient mice

A role for nitric oxide (NO) in wound healing has been proposed; however, the absolute requirement of NO for wound healing in vivo and the contribution of endothelial NO synthase (eNOS) have not been determined. Experiments were carried out using eNOS gene knockout (KO) mice to determine the requirement for eNOS on wound closure and wound strength. Excisional wound closure was significantly delayed in the eNOS KO mice (29.4 +/- 2.2 days) compared with wild-type (WT) controls (20.2 +/- 0.4 days). At 10 days, incisional wound tensile strength demonstrated a 38% reduction in the eNOS KO mice. Because effective wound repair requires growth factor-stimulated angiogenesis, in vitro and in vivo angiogenesis assays were performed in the mice to assess the effects of eNOS deficiency on angiogenesis. Endothelial cell sprouting assays confirmed in vitro that eNOS is required for proper endothelial cell migration, proliferation, and differentiation. Aortic segments harvested from eNOS KO mice cultured with Matrigel demonstrated a significant reduction in endothelial cell sprouting and [(3)H]thymidine incorporation compared with WT mice at 5 days. Capillary ingrowth into subcutaneously implanted Matrigel plugs was significantly reduced in eNOS KO mice (2.67 +/- 0.33 vessels/plug) compared with WT mice (10.17 +/- 0.79 vessels/plug). These results clearly show that eNOS plays a significant role in facilitating wound repair and growth factor-stimulated angiogenesis.

Induction of haem oxygenase-1 nitric oxide and ischaemia in experimental solid tumours and implications for tumour growth

Induction of haem oxygenase-1 (HO-1) as well as nitric oxide (NO) biosynthesis during tumour growth was investigated in an experimental solid tumour model (AH136B hepatoma) in rats. An immunohistochemical study showed that the inducible isoform of NO synthase (iNOS) was localized in monocyte-derived macrophages, which infiltrated interstitial spaces of solid tumour, but not in the tumour cells. Excessive production of NO in the tumour tissue was unequivocally verified by electron spin resonance spectroscopy. Tumour growth was moderately suppressed by treatment with either Nomega-nitro-L-arginine methyl ester (L-NAME) or S-methylisothiourea sulphate (SMT). In contrast, HO-1 was found only in tumour cells, not in macrophages, by in situ hybridization for HO-1 mRNA. HO-1 expression in AH136B cells in culture was strongly enhanced by an NO (NO+) donor S-nitroso-N-acetyl penicillamine. HO-1 mRNA expression in the solid tumour in vivo decreased significantly after treatment with low doses of NOS inhibitors such as L-NAME and SMT (6-20 mg kg(-1)). However, the level of HO-1 mRNA in the solid tumour treated with higher doses of NOS inhibitor was similar to that of the solid tumour without NOS inhibitor treatment. Strong induction of HO-1 was also observed in solid tumours after occlusion or embolization of the tumour-feeding artery, indicating that ischaemic stress which may involve oxidative stress triggers HO-1 induction in the solid tumour. Lastly, it is of great importance that an HO inhibitor, zinc protoporphyrin IX injected intra-arterially to the solid tumour suppressed the tumour growth to a great extent. In conclusion, HO-1 expression in the solid tumour may confer resistance of tumour cells to hypoxic stress as well as to NO-mediated cytotoxicity.

Association between arthroscopic diagnosis of temporomandibular joint osteoarthritis and synovial fluid nitric oxide levels

OBJECTIVE

The purpose of this study was to determine whether there is a relationship between synovial fluid levels of nitric oxide and clinical and arthroscopic findings of synovitis or cartilaginous degeneration.

STUDY DESIGN

Arthroscopic surgery was performed on 20 joints in 15 female patients with internal derangement and osteoarthritis of the temporomandibular joint. Synovial fluid aspirates were obtained immediately before arthroscopy. Synovial fluid was also obtained from 14 joints of 11 female asymptomatic volunteers. The concentration of nitrite in the fluid recovered from each temporomandibular joint was measured through use of a highly sensitive and specific chemiluminescence detection method, calibrated per 1 mg of synovial fluid protein and expressed as nitric oxide; the result was then compared with clinical and arthroscopic findings of synovitis and cartilaginous degeneration.

RESULTS

Significantly higher levels of nitric oxide (median, 0.331 micromol/mg) were seen in the patients with internal derangement and osteoarthritis than in the control group (median, 0.001 micromol/mg; P<.0001). Synovial fluid from joints with pain in the joint area had significantly higher levels of nitric oxide than did fluid from joints without such pain. Synovial fluid from joints with degenerative changes (median, 0.467 micromol/mg) had significantly higher levels of nitric oxide than did fluid from joints without osteoarthritis (median, 0.057 micromol/mg; P<.05). Although the levels of nitric oxide in synovial fluid aspirates were markedly elevated in some joints with synovitis, there was no correlation between the levels of nitric oxide and the presence of synovitis.

CONCLUSIONS

The findings indicate that increased levels of nitric oxide are involved in the pathogenesis of cartilaginous degeneration of the temporomandibular joint.

Human monocytic U937 cells kill Salmonella in vitro by NO-independent mechanisms

Nitric oxide (NO) has a central role in host defense against intracellular microbes. HLA-B27 has been shown to directly modulate host-microbe interaction in vitro, leading to the impaired elimination of Salmonella in human monocytic U937 cells. Here, we studied whether impaired elimination of Salmonella would result from differences in NO production between HLA-B27- and HLA-A2-transfected U937 cells. Both human monocytic transfectants produced NO equally well and killed Salmonella via NO-independent mechanisms.

Co-operation between endothelin and nitric oxide in promoting endothelial cell migration and angiogenesis

1. Among the diverse functions of endothelins (ET), their role in the remodelling of blood vessels remains poorly examined. In the present review, we summarize findings obtained in our laboratory and present four independent lines of evidence to support this novel function. We also demonstrate that the motogenic and angiogenic effects of ET are mediated via the ETB receptor and that the functional endothelial nitric oxide synthase (NOS) is requisite for this action. 2. We demonstrated that ET stimulates transmigration of endothelial cells in a modified Boyden chamber and accelerates endothelial wound healing acting via ETB receptors. 3. In genetically engineered Chinese hamster ovary cells expressing either ETB receptor or endothelial NOS or both, application of ET results in accelerated cell migration only when the receptor and the enzyme are coexpressed. Application of antisense oligonucleotides producing a specific knockdown of the endothelial NOS results in the loss of ET ability to stimulate endothelial cell migration in response to ET. 4. Finally, using a novel model of in vivo angiogenesis, we were able to demonstrate that ET enhances formation of new vessels, but this effect requires functional endothelial NOS. 5. The described phenomenon of NO production, serving as a prerequisite for endothelial cell locomotion in response to activation of ETB receptor may explain a host of pathophysiological observations on inadequate angiogenesis despite enhanced generation of ET-1. 6. Based on the contribution of endothelial cell migration to angiogenesis, these data may implicate insufficient NO production in pathological states (e.g. atherosclerosis, heart failure and hypertension) in the inappropriate response to angiogenic stimuli.

Nitric oxide production and nitric oxide synthase type 2 expression by human mononuclear phagocytes: a review

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Nitric oxide synthase activity in human squamous cell carcinoma of the head and neck

OBJECTIVES

To test whether nitric oxide synthase (NOS) is expressed in primary otolaryngologic tumors and whether this expression is associated with the degree of malignancy.

STUDY DESIGN

Twenty-six samples from the primary localization of human pharyngolaryngeal squamous cell carcinoma.

MATERIALS AND METHODS

the activity of calcium-dependent and calcium-independent NOS was analyzed by the conversion of L-[14C]-arginine into L-[14C]-citrulline.

RESULTS

NOS activity is below detectable levels in pharyngolaryngeal mucosa from noncancer patients. In the primary localization of the tumor, calcium-independent NOS activity is maximal at early stages of tumor growth, whereas calcium-dependent activity increases from early to advanced stages.

CONCLUSIONS

These data suggest that tumor growth and malignancy is associated with a change in the enzymatic source of NO from calcium-independent NOS to calcium-dependent NOS isoform in primary localization. These data suggest that the inhibition of calcium-independent NOS activity in early stages and/or inhibition of calcium-dependent NOS activity in later stages could delay growth of solid tumors.

Nitric oxide suppresses bFGF- and IL-1-alpha-mediated but not VEGF165-mediated angiogenesis in natively vascularized mammalian tissue

Using the rat mesenteric window angiogenesis assay, we studied the systemic effect of the nitric oxide synthase inhibitor Nw-nitro-L-arginine methyl ester, L-NAME, on angiogenesis induced by basic fibroblast growth factor (bFGF), interleukin-1-alpha (IL-1) or vascular endothelial growth factor (VEGF165). Using technically independent morphometric and image analysis methods, the angiogenic response was quantified in variables related to (i) microvascular spatial extension and (ii) microvascular density. The test tissue, which is natively vascularized and lacks significant angiogenesis physiologically, was unaffected by surgical intervention. Two daily intraperitoneal injections of bFGF (2.20 nmole), IL-1 (1.18 nmole) and VEGF165 (480 pmole) for 5 days elicited significant angiogenesis in the mesenteric windows. L-NAME (0.5 g/L in drinking water) caused further enhancement of the angiogenic response produced by human recombinant bFGF (p<0.001), bovine purified bFGF (p<0.05) or murine recombinant IL-1 (p<0.05). In contrast, the L-NAME treatment did not affect the angiogenic response produced by human and murine recombinant VEGF165. These data suggest that nitric oxide can act as an endogenous suppressor of mammalian de novo angiogenesis, which is a new finding, and, moreover, that angiogenesis induced by VEGF165 on the one hand and by bFGF and IL-1 on the other in the rat mesenteric window depends on different pathways.

Nitric oxide synthase activity in fresh cells from ovarian tumour tissue: relationship of enzyme activity with clinical parameters of patients with ovarian cancer

Recent studies suggest a dual role for nitric oxide (NO) in tumour biology. High concentrations of NO can mediate tumouricidal activity, whereas lower concentrations have been shown to promote tumour growth. In this study, NO synthase (NOS) activity was investigated in cells that were prepared from tissue from primary and metastatic sites and from malignant effusions in 41 cases of suspected ovarian cancer. NO biosynthesis, determined by nitrite + nitrate (NOx) accumulation in medium from cultured cells prepared from disaggregated tumours or effusions and indicative of the inducible NO synthase isoform, was detected in 37% of the cases investigated (range 10.2-114 microM). There was a significant relationship between NOx and tumour differentiation (P = 0.014), with NOx being significantly higher for the more differentiated tumours. NOS activity, determined by the conversion of radiolabelled L-arginine to citrulline by tissue or cell extracts, was detected in 29% of cases (range 0.9-6.9 pmol/min per mg of protein), with all samples tested being moderately or poorly differentiated. Seventy percent of this activity was calcium dependent, indicative of constitutive NOS isoforms. Morphological and immunohistochemical assessment of tumour samples indicated a significant relationship between high macrophage content and NOS activity (as NOx biosynthesis) (rs = 0.726, N = 16, P < 0.01). The relationship between NOS expression, immune response, and disease progression is complex and not simply dependent on the differentiation status of ovarian cancer.

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.

Autoregulation of angiogenesis by cells of the vessel wall

The cells of the vessel wall can regulate angiogenesis by producing growth factors, proteolytic enzymes, extracellular matrix components, cell adhesion molecules, and vasoactive factors. This property enables preexisting blood vessels to generate new vessels in the absence of exogenous angiogenic stimuli. Vascular autoregulation of angiogenesis can be studied by culturing rat aortic or venous explants in collagen gels under serum-free conditions. In this system, the combined effect of injury and exposure of explants to collagen triggers a self-limited angiogenic response. Interactions among endothelial cells, smooth muscle cells, and fibroblasts play a critical role in the regulation of this process. This chapter reviews the literature on angiogenesis, focusing on the vessel wall as a highly specialized and plastic tissue capable of regenerating itself through autocrine, paracrine, and juxtacrine mechanisms.