Continuous perivascular L-arginine delivery increases total vessel area and reduces neointimal thickening after experimental balloon dilatation

Fibroblasts mediate endothelium response to angiogenic cues in a newly developed 3D stroma engineered model

Three-dimensional stroma engineered models would enable fundamental and applicative studies of human tissues interaction and remodeling in both physiological and pathological conditions. In this work, we propose a 3D vascularized stroma model to be used as in vitro platform for drug testing. A pullulan/dextran-based porous scaffold containing pre-patterned microchannels of 100 μm diameter is used for co-culturing of fibroblasts within the matrix pores and endothelial cells to form the lumen. Optical clearing of the constructs by hyperhydration allows for in-depth imaging of the model up to 1 mm by lightsheet and confocal microscopy. Our 3D vascularized stroma model allows for higher viability, metabolism and cytokines expression compared to a monocultured vascular model. Stroma-endothelium cross-talk is then investigated by exposing the system to pro and anti-angiogenic molecules. The results highlight the protective role played by fibroblasts on the vasculature, as demonstrated by decreased cytotoxicity, restoration of nitric oxide levels upon challenge, and sustained expression of endothelial markers CD31, vWF and VEGF. Our tissue model provides a 3D engineered platform for in vitro studies of stroma remodeling in angiogenesis-driven events, known to be a leading mechanism in diseased conditions, such as metastatic cancers, retinopathies and ischemia, and to investigate related potential therapies.

L-Arginine-Nitric Oxide-Asymmetric Dimethylarginine Pathway and the Coronary Circulation: Translation of Basic Science Results to Clinical Practice

By 1980, it was thought that we already knew most of the major mechanisms regulating vascular tone. However, after the somewhat serendipity discovery that endothelium is involved in mediation of relaxation to acetylcholine, a whole new world opened up and we had to rewrite our concept regarding vascular function and its regulation (not to mention many other fields). The new player was an endothelium derived relaxing factor, which molecular constitution has been identified to be nitric oxide (NO). This review summarizes the major molecular steps concerning how NO is synthetized from L-arginine. Also, the fate of L-arginine is described via the arginase and methylation pathways; both of them are affecting substantially the level and efficacy of NO. In vitro and in vivo effects of L-arginine are summarized and controversial clinical findings are discussed. On the basis of the use of methylated L-arginines, the vasomotor effects of endothelial NO released to agonists and increases in flow/wall shear stress (a major biological stimulus) is summarized. In this review the role of NO in the regulation of coronary vascular resistance, hence blood flow, is delineated and the somewhat questionable clinical use of NO donors is discussed. We made an attempt to summarize the biosynthesis, role, and molecular mechanisms of endogenously produced methylated L-arginine, asymmetric dimethylarginine (ADMA) in modulating vascular resistance, affecting the function of the heart. Additionally, the relationship between ADMA level and various cardiovascular diseases is described, such as atherosclerosis, coronary artery disease (CAD), ischemia/reperfusion injuries, and different types of coronary revascularization. A novel aspect of coronary vasomotor regulation is identified in which the pericardial fluid ADMA and endothelin play putative roles. Finally, some of the open possibilities for future research on L-arginine-NO-ADMA signaling are highlighted.

Mechanisms of post-intervention arterial remodelling

It has been appreciated over the past two decades that arterial remodelling, in addition to intimal hyperplasia, contributes significantly to the degree of restenosis that develops following revascularization procedures. Remodelling appears to be an adventitia-based process that is contributed to by multiple factors including cytokines and growth factors that regulate extracellular matrix or phenotypic transformation of vascular cells including myofibroblasts. In this review, we summarize the currently available information from animal models as well as clinical investigations regarding arterial remodelling. The factors that contribute to this process are presented with an emphasis on potential therapeutic methods to enhance favourable remodelling and prevent restenosis.

Stromal cell biology--a way to understand the evolution of cardiovascular diseases

Stromal cells, composed of fibroblasts, microvascular endothelial cells, immune cells and inflammatory cells, are critical determinants of the mechanical properties and function of the heart and vasculature, and the mechanisms whereby these types of cells are activated are important to understand the progression of cardiovascular diseases. Emerging studies have suggested that the activation of autocrine and paracrine signaling pathways by stromal cell-derived growth factors, cytokines and bioactive molecules contributes to disease progression. Disruption of the stromal network will result in alterations in the geometry and function in these organs. Interventions targeting the stromal cells (eg, myofibroblasts, microvascular endothelial cells, inflammatory cells) by pharmacological agents or direct gene delivery/small interfering RNA would be potential novel therapeutic strategies to prevent/attenuate the progression of cardiovascular disorders.

Mechanisms of disease: L-arginine in coronary atherosclerosis--a clinical perspective

L-arginine is the substrate of endothelial nitric oxide synthase and the main precursor of nitric oxide in the vascular endothelium, thus its effects are mediated largely by increases in nitric oxide production. L-arginine has antioxidant and antiapoptotic properties, increases smooth muscle relaxation, inhibits the expression of adhesion molecules and chemotactic peptides, decreases endothelin-1 expression, and inhibits platelet aggregation. This amino acid also improves endothelial function in patients with coronary artery disease and dilates human epicardial atheromatous coronary arteries. Despite the positive results from small case-control studies, it is still unclear whether chronic administration of L-arginine has any effect on clinical outcome in patients with coronary artery disease. In addition, other indirect strategies, such as the inhibition of arginase, could prove more effective at improving intracellular L-arginine bioavailability than exogenous L-arginine administration. The potential clinical usefulness of L-arginine, therefore, needs further evaluation in large, prospective clinical trials. Here, we present a critique of the existing literature about the role of L-arginine in the prevention of atherosclerosis.

Pulmonary vascular dilation induced by L-ARGININE: correlation with induction of endothelial nitric oxide synthase in a rabbit model

PURPOSE

To determine whether oral administration of L-ARGININE induces pulmonary vascular dilation, and if this pulmonary vascular dilation correlates with induction of endothelial nitric oxide synthase (eNOS) in a rabbit model.

MATERIAL AND METHODS

Seven rabbits were fed with L-ARGININE dissolved in tap water. The degree of pulmonary vascular dilation was determined using thin-section computed tomography and the concentration of serum nitrite was measured. They were compared with four control animals. The pulmonary vascular dilation was correlated to serum levels of nitrite. Lung tissues were examined for induction of eNOS by immunohistochemistry.

RESULTS

An increased degree of pulmonary vascular dilation was found in the L-ARGININE-fed group compared to the control group (P<0.05). Serum levels of nitrite in the L-ARGININE-fed group were higher than those in the control group (P<0.05). Pulmonary vascular dilation correlated with serum levels of nitrite (r2=0.95, P<0.05). Induction of eNOS was increased in the L-ARGININE-fed group.

CONCLUSION

The administration of L-ARGININE causes pulmonary vascular dilation, which is most likely mediated via nitric oxide through increased induction of eNOS in a rabbit model.

Effect of L-NAME on the Synthesis of Plasma Fibrinogen in Mice

The effect of nitric oxide (NO) on plasma fibrinogen was investigated by treating mice with oral N(G)-nitro-L-arginine-methyl ester (L-NAME), a non-selective NO synthase (NOS) inhibitor. Treatment with L-NAME significantly increased the concentration of plasma fibrinogen and hepatic expression of the alpha- and beta-chains of fibrinogen, whereas plasma NO(2)(-) level and hepatic expression of endothelial NOS (eNOS) mRNA were significantly decreased. These results suggest that L-NAME treatment can increase plasma fibrinogen levels via an increase in expression of fibrinogen mRNA in the liver, and NO may be involved in plasma fibrinogen increase.

Pharmacologic inhibition of nitric oxide synthases and cyclooxygenases enhances intimal hyperplasia in balloon-injured rat carotid arteries

OBJECTIVE

Extensive proliferation and migration of smooth muscle cells (SMCs) contribute to development of fibromuscular intimal hyperplasia in response to balloon catheter-induced injury of the left carotid artery in Fischer 344 rats. The purpose of the present study was to test the hypothesis that endogenously generated nitric oxide (NO) and prostaglandins act synergistically to limit the extent of neointimal hyperplasia.

METHODS

The left carotid artery of Fischer 344 rats was injured with a 2F balloon catheter. The following treatment was initiated 24 hours before arterial injury, and was continued for 2 weeks: N-nitro-l-arginine (L-NA; 10 mg/kg/d, in drinking water), indomethacin (1.5 mg/kg/d per gavage), and L-NA (10 mg/kg/d) plus indomethacin (1.5 mg/kg/d). After application of an overdose of pentobarbital animals were formalin-fixed. Subsequently, paraffin-embedded cross sections of the uninjured and injured carotid arteries were analyzed morphometrically. SMC proliferation was determined by incorporation of 5-bromo-2'-deoxyuridine.

RESULTS

Two weeks after injury, L-NA caused a 1.29-fold +/- 0.29-fold (mean +/- SD; n = 14; P <.05) increase in the intima-media ratio, compared with control animals, whereas indomethacin had no effect. Combined treatment with L-NA plus indomethacin further increased intima-media ratio (1.65-fold +/- 0.5-fold over control; n = 14; P <.05). SMC proliferation in the neointima of rats treated with L-NA and L-NA plus indomethacin was elevated. Furthermore, neointimal cell density (nuclei per square millimeter) was reduced after combined inhibition of cyclooxygenases and NO synthases.

CONCLUSION

The present results of pharmacologic NO synthase and cyclooxygenase inhibition suggest that NO and prostaglandins are part of an endogenous growth inhibitory mechanism that synergistically suppresses intimal thickening.

CLINICAL RELEVANCE

The role of cyclooxygenase-1 (COX1) and cyclooxygenase-2 (COX2) during vascular recurrent stenosis and atherosclerosis is not clear yet. In particular, the effects of selective COX2 inhibitors on the frequency of cardiovascular events is still controversial. It is shown here in rats that the application of a non-selective COX inhibitor does not affect arterial stenosis. However, the concurrent inhibition of endogenous nitric oxide generation and COX1 or COX2 causes overshooting neointimal hyperplasia. These results suggest that increased vascular stenosis can result from administration of drugs that pharmacologically block 2 or more inhibitory pathways that normally counterbalance the effect of promotors of neointimal hyperplasia.

In-stent restenosis limitation with stent-based controlled-release nitric oxide: initial results in rabbits

PURPOSE

To evaluate effect of controlled stent-based release of an NO donor to limit in-stent restenosis in rabbits.

MATERIALS AND METHODS

Bioerodable microspheres containing NO donor or biodegradable polymer (polylactide-co-glycolide-polyethylene glycol) were prepared and loaded in channeled stents. Daily concentrations of NO release from NO-containing microspheres were assayed in vitro. NO- and polymer-containing (control) microsphere-loaded stents were deployed in aortas of New Zealand white rabbits (n = 8). Aortas with stents were harvested at 7 (n = 5) and 28 days (n = 3) and evaluated for cyclic guanosine monophosphate (cGMP) levels (7 days), number of proliferating cell nuclear antigen-positive cells (7 days), and intima-to-media ratio (7 and 28 days), with statistical significance evaluated by using one-way analysis of variance.

RESULTS

NO-containing microspheres released NO with an initial bolus in the 1st week, followed by sustained release for the remaining 3 weeks. Significant increase in cGMP levels and decrease in proliferating cell nuclear antigen-positive cells were found at 7 days for the NO-treated group relative to controls (P <.05). Intima-to-media ratio in the NO-treated group was reduced by 46% and 32% relative to controls at 7 and 28 days, respectively (mean, 0.14 +/- 0.01 [standard error] vs 0.26 +/- 0.02 at 7 days, P <.01; 1.34 +/- 0.05 vs 1.98 +/- 0.08 at 28 days, P <.01).

CONCLUSION

Stent-based controlled release of NO donor significantly reduces in-stent restenosis and is associated with increase in vascular cGMP and suppression of proliferation.

L-arginine in cardiovascular disease: dream or reality?

L-arginine is the substrate for endothelial nitric oxide synthase (eNOS), and the precursor for the synthesis of nitric oxide (NO). This amino acid exerts a number of actions in the cardiovascular system, mainly through the production of NO. However, it also has a number of NO-independent properties, such as the ability to regulate blood and intracellular pH and the effect on the depolarization of endothelial cell membranes. It also has antihypertensive and antioxidant properties, it influences blood viscosity and the coagulation/fibrinolysis system, and it affects the metabolism of glucose, lipids and proteins. L-arginine influences a number of atherosclerosis risk factors such as hypercholesterolemia, hypertension and smoking, improving endothelial function in these patients. However, it does not affect endothelial function in patients with diabetes mellitus. The role of L-arginine in coronary artery disease is still controversial, but it seems that oral or parenteral administration of this amino acid restores endothelial function in the brachial artery and improves coronary microcirculation. The role of L-arginine in heart failure is currently under investigation, and the first results are rather hopeful. In conclusion, L-arginine seems to provide a hopeful prospect for the treatment of cardiovascular diseases. However, more data derived from large-scale prospective studies evaluating the effects of long-term treatment with L-arginine are needed.

Minimal duration of oral matrix metalloproteinase inhibition to prevent constrictive arterial remodeling after balloon dilation in the pig

PURPOSE

To determine the minimal duration of oral matrix metalloproteinase (MMP) inhibition to prevent constrictive remodeling after balloon dilation.

MATERIALS AND METHODS

In 37 nonatherosclerotic pigs, balloon dilation was performed in 145 peripheral arteries. Pigs were treated with an MMP inhibitor for 2, 7, 14, 28, or 42 days, or they served as controls and were killed 42 days after intervention. Arteries were visualized with angiography and intravascular ultrasonography.

RESULTS

A 69% reduction in late vessel area (VA) loss was achieved after 14 days of treatment: 1.27 mm(2) +/- 0.55 (standard error of the mean [SEM]) versus 4.04 mm(2) +/- 0.93 (SEM) in the control group (P =.1). A consistent inhibition of late VA loss was observed in the 28-day (0.89 mm(2) +/- 0.83 [SEM], P =.03) and 42-day (0.74 mm(2) +/- 0.66 [SEM], P =.02) groups treated with the MMP inhibitor. After 14 and 28 days of treatment, late lumen area loss was 65% and 55% of control values, and it decreased to 41% (P =.04) after 42 days of treatment.

CONCLUSION

MMP inhibition for 14-28 days is sufficient to inhibit constrictive remodeling after balloon dilation. This implies that an essential MMP-dependent initiator of constrictive remodeling was mainly active in the first 2 weeks after intervention.

Comparative Trial of Local Pharmacotherapy withl-Arginine, r-Hirudin, and Molsidomine to Reduce Restenosis after Balloon Angioplasty of Stenotic Rabbit Iliac Arteries

PURPOSE

To determine if local application of L-arginine, r-hirudin, or molsidomine significantly reduces restenosis after balloon angioplasty in stenotic rabbit iliac arteries.

MATERIALS AND METHODS

Thirty-one male cholesterol-fed New Zealand white rabbits underwent balloon dilation of both common iliac arteries to induce arterial stenosis. Four weeks later, one stenotic iliac artery was simultaneously dilated and received local application of L-arginine (210 mg/mL, n = 7), r-hirudin (0.5 mg/mL, n = 8), or molsidomine (0.2 mg/mL, n = 8) with a channeled balloon catheter. On the contralateral side, 0.9% saline was injected as a control. In eight sham animals, saline was applied to one iliac artery and balloon dilation to only the contralateral artery. Six weeks after local treatment, vessels were harvested, and computerized morphometric and immunohistologic analyses were performed.

RESULTS

Application of drugs resulted in a significant reduction of neointimal area as follows: 53% with L-arginine (1.01 mm(2) vs. 2.17 mm(2), P <.05), 43% with molsidomine (1.04 mm(2) vs. 1.89 mm(2), P <.05), and 20% with r-hirudin (1.79 mm(2) vs. 2.24 mm(2), P <.05). Infusion of saline led to a significant increase (50%, 1.21 mm(2) vs. 1.93 mm(2), P <.05) in neointimal area compared with balloon dilation alone. Immunohistologic findings showed a significant reduction of macrophages (5.0% vs. 10.2%, P <.05) and proliferating cells (6.2% vs. 10.6%, P <.05) in the neointima after local application of L-arginine.

CONCLUSION

Reduction of neointimal area was significant for L-arginine and molsidomine but not for r-hirudin. Saline infusion caused significant arterial trauma, resulting in additional neointimal proliferation.

Therapeutic modification of the L-arginine-eNOS pathway in cardiovascular diseases

L-Arginine is the substrate for nitric oxide production. Endothelium dysfunction could be attributed to L-arginine deficiency or the presence of L-arginine endogenous inhibitors. This hypothesis leads to the assumption that provision of L-arginine could be the key for endothelial function improvement. Many studies have proven that L-arginine has a beneficial effect on endothelium dependent vasoreactivity, as well as on the interaction between vascular wall, platelets and leucocytes. Therefore, individuals with risk factors for atherosclerosis and patients with coronary artery disease or heart failure, could benefit from therapy with L-arginine.

Nitric oxide and postangioplasty restenosis: pathological correlates and therapeutic potential

Balloon angioplasty revolutionized interventional cardiology as a nonsurgical procedure to clear a diseased artery of atherosclerotic blockage. Despite its procedural reliability, angioplasty's long-term outcome can be compromised by restenosis, the recurrence of arterial blockage in response to balloon-induced vascular trauma. Restenosis constitutes an important unmet medical need whose pathogenesis has yet to be understood fully and remains to be solved therapeutically. The radical biomediator, nitric oxide (NO), is a natural modulator of several processes contributing to postangioplasty restenosis. An arterial NO deficiency has been implicated in the establishment and progression of restenosis. Efforts to address the restenosis problem have included trials evaluating a wide range of NO-based interventions for their potential to inhibit balloon-induced arterial occlusion. All types of NO-based interventions yet investigated benefit at least one aspect of balloon injury to a naive vessel in a laboratory animal without inducing significant side effects. The extent to which this positive, albeit largely descriptive, body of experimental data can be translated into the clinic remains to be determined. Further insight into the pathogenesis of restenosis and the molecular mechanisms by which NO regulates vascular homeostasis would help bridge this gap. At present, NO supplementation represents a unique and potentially powerful approach to help control restenosis, either alone or as a pharmaceutical adjunct to a vascular device.

Restenosis: a challenge for pharmacology

The quest for an anti-restenotic drug continues to be a major challenge in the field of cardiovascular pharmacology because most therapies with proven efficacy in experimental neointima models have failed to limit restenosis. Some drug classes, including glycoprotein IIb/IIIa antagonists, nitric oxide donors and the antioxidant probucol, have recently demonstrated potential benefits in clinical trials. Progress in the development of local delivery systems for administration of drugs, antisense oligonucleotides or genes, in combination with an improved understanding of the pathogenesis of restenosis holds promise for ultimate pharmacotherapy of this condition.

Nitric oxide (NO)-related pharmaceuticals: contemporary approaches to therapeutic NO modulation

The biologically important gaseous radical, nitric oxide (NO), is a versatile chemical entity that enters into regulatory, protective, and adverse interactions with biomolecules and cells, in some cases through NO-derived nitrogen oxide species. Both excess tissue NO and its insufficiency have been implicated in the genesis or evolution of several important disease states. The associated medical needs and commercial opportunities have fostered attempts to modulate tissue NO tone for symptomatic benefit or therapeutic gain. State-of-the-art strategies for NO modulation in contemporary drug discovery and development encompass sexual dysfunction, cardiovascular, and antiinflammatory indications. Increased understanding of NO's physiological chemistry and ways to target its pharmacology appear critical to the successful clinical exploitation of NO's diverse properties. Integration of research on both the basic science of NO's mechanistic biology and the applied science of drug discovery and development represents a millennium mandate to the pharmaceutical industry in the area of NO-related therapeutics.

Mechanisms of vascular atrophy and fibrous cap disruption

The process of plaque destabilization and rupture remains an area of intense investigation. While reductions in lumen cross-sectional area induced by early, non-occlusive lesions are compensated by remodeling and expansion of the artery, further plaque enlargement leads to an uncompensated reduction in lumen area and an increase in surface shearing forces. We hypothesize that these local increases in wall shear stress lead to a reduction in smooth muscle cell proliferation and increase in cell death. Using a primate prosthetic graft model, we have observed that alterations in nitric oxide and platelet-derived growth factor metabolism are important regulators of intimal growth and regression. We suggest that these factors may also be influential in the process of fibrous cap atrophy and plaque rupture.