Enzyme Nitric Oxide Synthase Research Articles

Diabetoporosis: Role of nitric oxide.

Diabetoporosis, diabetic-related decreased bone quality and quantity, is one of the leading causes of osteoporotic fractures in subjects with type 2 diabetes (T2D). This is associated with lower trabecular and cortical bone quality, lower bone turnover rates, lower rates of bone healing, and abnormal posttranslational modifications of collagen. Decreased nitric oxide (NO) bioavailability has been reported within the bones of T2D patients and can be considered as one of the primary mechanisms by which diabetoporosis is manifested. NO donors increase trabecular and cortical bone quality, increase the rate of bone formation, accelerate the bone healing process, delay osteoporosis, and decrease osteoporotic fractures in T2D patients, suggesting the potential therapeutic implication of NO-based interventions. NO is produced in the osteoblast and osteoclast cells by three isoforms of NO synthase (NOS) enzymes. In this review, the roles of NO in bone remodeling in the normal and diabetic states are discussed. Also, the favorable effects of low physiological levels of NO produced by endothelial NOS (eNOS) versus detrimental effects of high pathological levels of NO produced by inducible NOS (iNOS) in diabetoporosis are summarized. Available data indicates decreased bone NO bioavailability in T2D and decreased expression of eNOS, and increased expression and activity of iNOS. NO donors can be considered novel therapeutic agents in diabetoporosis.

The Effects of Rapamycin and 3-Methyladenine on Nitric Oxide Synthase Enzymes in Cisplatin-Induced Neurotoxicity

The Effects of Rapamycin and 3-Methyladenine on Nitric Oxide Synthase Enzymes in Cisplatin-Induced Neurotoxicity

Hypoxia-induced expression of neuronal nitric oxide synthase in astrocytes of human corpus callosum.

Nitric oxide (NO) is a gaseous neurotransmitter largely diffused in the brain; among other functions, it regulates the cerebral blood flow in response to hypoxia. NO can be synthetized by three different isoforms of the enzyme NO synthase: neuronal (nNOS), typical of neurons, endothelial and inducible. The aim of this study was to assess nNOS expression in human corpus callosum (CC) astrocytes, and its relationship with the hypoxia duration. Autoptic samples of CC from adult human subjects have been processed with immunohistochemistry and immunofluorescence using antibodies anti-nNOS and anti-glial fibrillary acidic protein (GFAP), the astrocyte marker. Results demonstrated for the first time the presence of nNOS-immunopositive astrocytes in the human CC. In particular, nNOS-positive astrocytes were absent in subjects deceased after a short hypoxia; their number and labeling intensity, however, increased with hypoxia prolongation. Neuronal NOS immunopositivity of CC astrocytes seems thus related to the hypoxia duration and the consequent brain damage.

MOLECULAR DYNAMIC SIMULATION OF ASIATIC ACID DERIVATIVES COMPLEX WITH INDUCIBLE NITRIC OXIDE SYNTHASE ENZYME AS AN ANTI-INFLAMMATORY

Objective: The aim of this study was to determine the stability interaction of asiatic acid derivatives (AA) complex with inducible nitric oxide synthase (iNOS) enzyme as an anti-inflammatory using Molecular Dynamic (MD) simulation.
 Methods: The methods were consisting of validation of molecular docking, molecular docking to calculate binding affinity within the complex between the compounds and iNOS enzyme by using MMGBSA (Molecular Mechanics/Generalized Born Surface Area), and MD system preparation, MD production as well as MD analysis using AMBER18.
 Results: The result of validation and molecular docking were AA5 has the most negative Gibbs energy that is -9.17 kcal/mol, which has better binding affinity than other derivatives than other derivatives. The molecular dynamics simulation of the modified structure of asiatic acid showed that binding energy value and RMSD of AA5, AA6 and AA9 have a lower value compared to arginine as a substrate of iNOS enzyme. Molecular Dynamics that have been occurred to the best three compounds chosen shown good result in terms of stability after 100 ns length simulation. And the lowest binding affinity has been achieved by a compound called AA5. Out of all ligands that have been simulated shown that their binding affinity was lower than AA5 that reached-44.6753 kcal/mol.
 Conclusion: This studies conclude that AA5 considerably more potential as a selective inhibitor of iNOS enzyme as an anti-inflammatory.

Pan-Cancer Analysis of NOS3 Identifies Its Expression and Clinical Relevance in Gastric Cancer.

Background: NOS3 (endothelial NOS, eNOS) is a member of the nitric oxide synthase (NOS) enzyme family, mainly participating in nitric oxide (NO) generation. NOS3 has been reported to inhibit apoptosis and promote angiogenesis, proliferation, and invasiveness. However, the expression pattern of NOS3 and its diagnostic and prognostic potential has not been investigated in a pan-cancer perspective.Methods: Data from the Genotype-Tissue Expression (GTEx), the Cancer Genome Atlas (TCGA), the Cancer Cell Line Encyclopedia (CCLE), and the Cancer Therapeutics Response Portal (CTRP) were employed and NOS3 expression was comprehensively analyzed in normal tissues, cancer tissues, and cell lines. Immunohistochemical staining of tissue sections were used to validate the prognostic role of NOS3 in gastric cancer patients. GSVA and GSEA analyses were performed to investigate signaling pathways related to NOS3 expression.Results: In normal tissues, NOS3 was expressed highest in the spleen and lowest in the blood. NOS3 expression was increased in stomach adenocarcinoma (STAD) and significantly associated with poor prognosis of patients. Immunohistochemical staining validated that NOS3 was an independent prognostic factor of gastric cancer. Several canonical cancer-related pathways were found to be correlated with NOS3 expression in STAD. The expression of NOS3 was related to the response to QS-11 and brivinib in STAD.Conclusions: NOS3 was an independent prognostic factor for patients with STAD. Increased expression of NOS3 influenced occurrence and development of STAD through several canonical cancer-related pathways. Drug response analysis reported drugs to suppress NOS3. NOS3 might be a novel target for gastric cancer treatment.

Cyanobacterial NOS expression improves nitrogen use efficiency, nitrogen-deficiency tolerance and yield in Arabidopsis

Developing strategies to improve nitrogen (N) use efficiency (NUE) in plants is a challenge to reduce environmental problems linked to over‐fertilization. The nitric oxide synthase (NOS) enzyme from the cyanobacteria Synechococcus PCC 7335 (SyNOS) has been recently identified and characterized. SyNOS catalyzes the conversion of arginine to citrulline and nitric oxide (NO), and then approximately 75 % of the produced NO is rapidly oxidized to nitrate by an unusual globin domain in the N-terminus of the enzyme. In this study, we assessed whether SyNOS expression in plants affects N metabolism, NUE and yield. Our results showed that SyNOS-expressing transgenic Arabidopsis plants have greater primary shoot length and shoot branching when grown under N-deficient conditions and higher seed production both under N-sufficient and N-deficient conditions. Moreover, transgenic plants showed significantly increased NUE in both N conditions. Although the uptake of N was not modified in the SyNOS lines, they showed an increase in the assimilation/remobilization of N under conditions of low N availability. In addition, SyNOS lines have greater N-deficiency tolerance compared to control plants. Our results support that SyNOS expression generates a positive effect on N metabolism and seed production in Arabidopsis, and it might be envisaged as a strategy to improve productivity in crops under adverse N environments.

Nitric Oxide and S-Nitrosylation in Cardiac Regulation: G Protein-Coupled Receptor Kinase-2 and β-Arrestins as Targets.

Cardiac diseases including heart failure (HF), are the leading cause of morbidity and mortality globally. Among the prominent characteristics of HF is the loss of β-adrenoceptor (AR)-mediated inotropic reserve. This is primarily due to the derangements in myocardial regulatory signaling proteins, G protein-coupled receptor (GPCR) kinases (GRKs) and β-arrestins (β-Arr) that modulate β-AR signal termination via receptor desensitization and downregulation. GRK2 and β-Arr2 activities are elevated in the heart after injury/stress and participate in HF through receptor inactivation. These GPCR regulators are modulated profoundly by nitric oxide (NO) produced by NO synthase (NOS) enzymes through S-nitrosylation due to receptor-coupled NO generation. S-nitrosylation, which is NO-mediated modification of protein cysteine residues to generate an S-nitrosothiol (SNO), mediates many effects of NO independently from its canonical guanylyl cyclase/cGMP/protein kinase G signaling. Herein, we review the knowledge on the NO system in the heart and S-nitrosylation-dependent modifications of myocardial GPCR signaling components GRKs and β-Arrs.

The expression of the nitric oxide synthase enzyme in periodontal disease and orofacial pain: systematic review

ABSTRACT BACKGROUND AND OBJECTIVES The literature suggests that the enzyme nitric oxide synthase (NOS) plays an important role in both periodontal disease (PD) and orofacial pain (OP), although few studies associate these two conditions simultaneously. The objective of this study was to evaluate the expression of the NOS enzyme in PD and OP, in comparison to those patients who did not present PD and/or OP. CONTENTS Seven electronic databases (Pubmed, Web of science, Scopus, Cochrane Library, BBO, LILACS, Clinical trial) were used to identify the potentially relevant studies published until April 2021. The research resulted in 1,960 studies, of which 11 were selected to be critically evaluated. Two independent reviewers selected titles and abstracts using the criteria defined in the PECO question (Population, Exposure, Comparison, Outcome). The methodological evaluation of the selected studies was carried out according to the Effective Public Health Practice Project (EPHPP). CONCLUSION: Scientific evidence demonstrated that NOS may play a key role in the pathogenesis of PD and OP, since its expression is increased in patients with these conditions. However, genetic studies on endothelial nitric oxide synthase (eNOS) gene mutations in patients with migraine and cluster headache did not indicate the expected susceptibility to pain. In addition, studies on the association of NOS expression in PD and OP, occurring simultaneously, are scarce. This review may support future research on NOS in two very common correlated diseases such as PD and OP.

Correlation between nasal nitric oxide and its metabolites, RANTES, IL-5 in allergic rhinitis

There have been two measurement methods for nasal nitric oxide (nNO): direct measurement of nNO and indirect measurement of NO metabolites or the NO synthase enzyme. The aim of this study is to investigate the difference in nNO between allergic rhinitis (AR) patients and the correlation of the direct measurement of nNO and indirect measurement of nNO metabolites, RANTES, and IL-5. Fifteen patients with AR, 15 patients with septal deviation as a control group were enrolled. We measured the nNO level using a chemiluminescence analyzer and the amount of NO metabolites, RANTES, and IL-5 in nasal lavage fluid using the ELISA method. Nasal NO levels were significantly higher in AR than the control (195.7 ± 39.6 vs 159.4 ± 25.8 ppb, P = 0.027). NO metabolites, IL-5, and RANTES levels were higher in AR, but there was no statistically significant difference. There was no significant correlation between nNO and nNO metabolites, RANTES, IL-5, and clinical parameters except for the olfactory test score in AR. There was a negative correlation between nNO and the olfactory test score in AR ( r = −0.590, P = 0.034). Nasal NO concentration increased in AR. However, nNO metabolites and IL-5, RANTES in nasal secretion did not show any correlation with nNO. Direct measurement of nNO could be a potentially useful biomarker of AR compared to indirect measurement of NO metabolites, cytokines, and chemokines in nasal secretion.

Calcitriol Supplementation Ameliorates Microvascular Endothelial Dysfunction in Vitamin D-Deficient Diabetic Rats by Upregulating the Vascular eNOS Protein Expression and Reducing Oxidative Stress.

Diabetes mellitus contributes to macro- and microvascular complications, leading to adverse cardiovascular events. This study examined the effects of vitamin D deficiency on the vascular function and tissue oxidative status in the microcirculation of diabetic rats and to determine whether these effects can be reversed with calcitriol (active vitamin D metabolite) supplementation. Streptozotocin-induced diabetic rats were fed for 10 weeks with control diet (DC) or vitamin D-deficient diet without (DD) or with oral calcitriol supplementation (0.15 μg/kg) in the last four weeks (DDS) (10 rats each group). A nondiabetic rat group that received control diet was also included (NR). After 10 weeks, rats were sacrificed; mesenteric arterial rings with and without endothelium were studied using wire myograph. Western blotting of the mesenteric arterial tissue was performed to determine the protein expression of endothelial nitric oxide synthase (eNOS) enzyme. Antioxidant enzyme superoxide dismutase (SOD) activity and oxidative stress marker malondialdehyde (MDA) levels in the mesenteric arterial tissue were also measured. The DC group had significantly lower acetylcholine-induced relaxation and augmented endothelium-dependent contraction, with reduced eNOS expression, compared to NR rats. In mesenteric arteries of DD, acetylcholine-induced endothelium-dependent and sodium nitroprusside-induced endothelium-independent relaxations were lower than those in DC. Calcitriol supplementation in DDS restored endothelium-dependent relaxation. Mesenteric artery endothelium-dependent contraction of DD was greater than DC; it was not affected by calcitriol supplementation. The eNOS protein expression and SOD activity were significantly lower while MDA levels were greater in DD compared to DC; these effects were not observed in DDS that received calcitriol supplementation. In conclusion, vitamin D deficiency causes eNOS downregulation and oxidative stress, thereby impairing the vascular function and posing an additional risk for microvascular complications in diabetes. Calcitriol supplementation to diabetics with vitamin D deficiency could potentially be useful in the management of or as an adjunct to diabetes-related cardiovascular complications.

The Oxidative Stress and Chronic Inflammatory Process in Chagas Disease: Role of Exosomes and Contributing Genetic Factors

Chagas disease is a neglected tropical disease caused by the flagellated protozoa Trypanosoma cruzi that affects several million people mainly in Latin American countries. Chagas disease has two phases, which are acute and chronic, both separated by an indeterminate time period in which the infected individual is relatively asymptomatic. The acute phase extends for 40-60 days with atypical and mild symptoms; however, about 30% of the infected patients will develop a symptomatic chronic phase, which is characterized by either cardiac, digestive, neurological, or endocrine problems. Cardiomyopathy is the most important and severe result of Chagas disease, which leads to left ventricular systolic dysfunction, heart failure, and sudden cardiac death. Most deaths are due to heart failure (70%) and sudden death (30%) resulting from cardiomyopathy. During the chronic phase, T. cruzi-infected macrophages respond with the production of proinflammatory cytokines and production of superoxide and nitric oxide by the NADPH oxidase 2 (NOX2) and inducible nitric oxide synthase (iNOS) enzymes, respectively. During the chronic phase, myocardial changes are produced as a result of chronic inflammation, oxidative stress, fibrosis, and cell death. The cellular inflammatory response is mainly the result of activation of the NF-κB-dependent pathway, which activates gene expression of inflammatory cytokines, leading to progressive tissue damage. The persisting production of reactive oxygen species (ROS) is the result of mitochondrial dysfunction in the cardiomyocytes. In this review, we will discuss inflammation and oxidative damage which is produced in the heart during the chronic phase of Chagas disease and recent evidence on the role of macrophages and the production of proinflammatory cytokines during the acute phase and the origin of macrophages/monocytes during the chronic phase of Chagas disease. We will also discuss the contributing factors and mechanisms leading to the chronic inflammation of the cardiac tissue during the chronic phase of the disease as well as the innate and adaptive host immune response. The contribution of genetic factors to the progression of the chronic inflammatory cardiomyopathy of chronic Chagas disease is also discussed. The secreted extracellular vesicles (exosomes) produced for both T. cruzi and infected host cells can play key roles in the host immune response, and those roles are described. Lastly, we describe potential treatments to attenuate the chronic inflammation of the cardiac tissue, designed to improve heart function in chagasic patients.

Striatal dopaminergic neurons as a potential target for GDNF based ischemic stroke therapy.

Glial cell-line-derived neurotrophic factor (GDNF) is a well-known regulatory neurotrophic factor on dopaminergic neurons. Several pathologies have been documented so far in case of any impairment in the dopaminergic system. This study aimed to investigate the potential protective role of lentiviral GNDF delivery on the small population of tyrosine hydroxylase (TH) positive dopamine producing striatal neurons after ischemic stroke. Fourteen C57BL/6J male mice (8-10 weeks) were intracerebrally treated with lentiviral GDNF (Lv-GDNF) or vehicle. Ten days after injections, cerebral ischemia was induced by blockage of the middle cerebral artery. Animals were terminated 72 h after ischemia, and their brains were taken for histological and molecular investigations. Following confirmation of GDNF overexpression, TH immunostaining and immunoblotting were used to evaluate the role of GDNF on dopaminergic neurons. Next, Fluro Jade C staining was implemented to examine the degree of neuronal degeneration at the damaged parenchyma. Neither the amount of TH positive dopaminergic neurons nor the expression of TH changed in the Lv-GDNF treated animals comparing to the vehicle group. On the other hand, GDNF exposure caused a significant increase in the expression of Nurr1, an essential transcription factor for dopaminergic neurons and Gap43, growth and plasticity promoting protein, in the ischemic striatum. Treatment with Lv-GDNF gave rise to a significant reduction in the number of degenerated neurons. Finally, enhanced GDNF expression also induced expression of an important stress-related transcription factor NF-κB as well as the nitric oxide synthase enzymes iNOS and nNOS in the contralesional hemisphere.

Role of Nitric Oxide in Neurodegeneration: Function, Regulation, and Inhibition.

Reactive nitrogen species (RNS) and reactive oxygen species (ROS), collectively known as reactive oxygen and nitrogen species (RONS), are the products of normal cellular metabolism and interact with several vital biomolecules including nucleic acid, proteins, and membrane lipids and alter their function in an irreversible manner which can lead to cell death. There is an imperative role for oxidative stress in the pathogenesis of cognitive impairments and the development and progression of neural injury. Elevated production of higher amounts of nitric oxide (NO) takes place in numerous pathological conditions, such as neurodegenerative diseases, inflammation, and ischemia, which occur concurrently with elevated nitrosative/oxidative stress. The enzyme nitric oxide synthase (NOS) is responsible for the generation of NO in different cells by conversion of L-arginine (Arg) to L-citrulline. Therefore, the NO signaling pathway represents a viable therapeutic target. Naturally occurring polyphenols targeting the NO signaling pathway can be of major importance in the field of neurodegeneration and related complications. Here, we comprehensively review the importance of NO and its production in the human body and afterwards highlight the importance of various natural products along with their mechanisms against various neurodegenerative diseases involving their effect on NO production.

What Determines the Selectivity of Arginine Dihydroxylation by the Nonheme Iron Enzyme OrfP?

The nonheme iron enzyme OrfP reacts with l-Arg selectively to form the 3R,4R-dihydroxyarginine product, which in mammals can inhibit the nitric oxide synthase enzymes involved in blood pressure control. To understand the mechanisms of dioxygen activation of l-Arg by OrfP and how it enables two sequential oxidation cycles on the same substrate, we performed a density functional theory study on a large active site cluster model. We show that substrate binding and positioning in the active site guides a highly selective reaction through C3 -H hydrogen atom abstraction. This happens despite the fact that the C3 -H and C4 -H bond strengths of l-Arg are very similar. Electronic differences in the two hydrogen atom abstraction pathways drive the reaction with an initial C3 -H activation to a low-energy 5 σ-pathway, while substrate positioning destabilizes the C4 -H abstraction and sends it over the higher-lying 5 π-pathway. We show that substrate and monohydroxylated products are strongly bound in the substrate binding pocket and hence product release is difficult and consequently its lifetime will be long enough to trigger a second oxygenation cycle.

Study on Role of Nitric Oxide and High Sensitive C - reactive protein in subjects with Coronary Heart Disease

Nitric Oxide (NO) where produced by endothelial nitric oxide synthase (eNOS) enzyme which are inhibited by C-reactive protein (CRP) which causes endothelial dysfunction and cardiovascular events. In the current study, we evaluated the association of NO with hs-CRP in subjects with coronary heart disease. This Case-Control study was conducted 60 CHD patients and 60 healthy controls in age group of 30 to 55 years at SRM Medical College Hospital and Research Centre on subjects attending the Cardiology and medicine OP. Blood samples were collected after overnight fasting for analysis of Lipid Profile, High sensitive C-reactive protein. Nitric Oxide and High sensitive C-reactive protein is measured by ELISA method and Lipid Profile is measured using Auto Analyzer AU480. Statistical analysis was done using Student ‘t’ test and Pearson correlation analysis used to the variable between two groups. The mean level of LDL-C (161.9±27.46) and hs-CRP (6.80±1.35) were significantly elevated in CHD subjects when compared to the normal healthy controls. And the mean level of Nitric Oxide (12.97±1.20) were decreased significantly in CHD group when compared to controls. Increased oxidative stress associated with low grade inflammation lead to diminished bioavailability of nitric oxide.

Novel Nitric Oxide Releasing Films Based on Inducible Nitric Oxide Synthase and Their Biomedical Applications

Although a tremendous number of biomaterials are labeled as biocompatible for blood-contacting medical devices, such as vascular grafts, stents, heart valves, and catheters, the thrombogenic nature of these materials can cause serious complications in patients, and eventually functional failure. There are two major limiting factors to clinical application of these materials: 1) platelet activation and thrombus formation, and 2) infection. Nitric oxide (NO) has been known to exert anti-thrombotic, anti-proliferative, and anti-inflammatory effects in the vasculature. Several polymers incorporate NO-generating substances in order to improve biocompatibility of blood-contacting medical devices. However, an important drawback for these NO-release materials is the finite stoichiometric amount of embedded NO that they contain, which could impact their function for long-term or semi-permanent types of implants. In addition, controlling the release rates of NO flux that can be emitted at the polymer/blood interface proved to be challenging, and often requires the addition of other components to the polymer. Therefore, we hypothesized that incorporating the enzyme nitric oxide synthase into polymeric films as functional catalytic units that generate NO would result its antithrombotic coatings with potentially unlimited amounts of NO released.In this project, we use layer-by-layer thin film building strategy to form layers of polyethyleneimine (PEI) and recombinant NOS enzymes as NO-releasing coatings. Charge-based layer-by-layer electrostatic adsorption allows for assembly of multi-component protein/PEI films with defined thickness and catalytic properties. When surfaces coated with PEI/NOS multilayered films are exposed to substrate arginine, a source of reducing equivalents, and other ingredients of the NOS reaction, nitric oxide is formed and released. In this work, we characterize the PEI/NOS thin films in terms of structure of NOS within the films as well as the amount of active NOS. Fourier transform infrared (FTIR) spectroscopic analysis was used to characterize structure-activity relationships of these NOS-containing thin films. We used cyclic voltammetry to determine the active enzyme concentration on the modified surfaces. We also examined how this activity relates to enzymatic activity in terms of NO released fluxes from the thin films. Finally, we assessed the functional performance of these films in terms of the extent to which they counteract platelet adhesion on the coated surfaces. To this end, we used platelet adhesion assays to determine how the number of platelets adsorbed on the PEI/NOS films is affected by the amount of NO released from the PEI/NOS thin films.

A Potential Involvement of Anandamide in the Modulation of HO/NOS Systems: Women, Menopause, and "Medical Cannabinoids".

Endocannabinoids and their receptors are present in the cardiovascular system; however, their actions under different pathological conditions remain controversial. The aim of our study was to examine the effects of anandamide (AEA) on heme oxygenase (HO) and nitric oxide synthase (NOS) systems in an estrogen-depleted rat model. Sham-operated (SO) and surgically induced estrogen-deficient (OVX) female Wistar rats were used. During a two-week period, a group of OVX rats received 0.1 mg/kg estrogen (E2) per os, while AEA-induced alterations were analyzed after two weeks of AEA treatment at the dose of 1.0 mg/kg. At the end of the experiment, cardiac activity and expression of HO and NOS enzymes, content of cannabinoid 1 receptor, as well as concentrations of transient potential vanilloid 1 (TRPV1) and calcitonin gene-related peptide (CGRP) were measured. Our results show that estrogen withdrawal caused a significant decrease in both NOS and HO systems, and a similar tendency was observed regarding the TRPV1/CGRP pathway. Two weeks of either AEA or E2 treatment restored the adverse changes; however, the combined administration of these two molecules did not result in a further improvement. In light of the potential relationship between AEA and HO/NOS systems, AEA-induced upregulation of HO/NOS enzymes may be a therapeutic strategy in estrogen-deficient conditions.

The effect of long term nicotine exposure on endothelial function in rats

Nicotine is one of the main chemicals in the cigarettes responsible for addiction formation. Many researches investigating the effects of nicotine on coronary heart disease and atherosclerosis have been published. The robustness of endothelial cells is very important in the development of atherosclerosis. The aim of this study is to evaluate the effect of nicotine exposure on the indicators of endothelial function either by examining the vascular reactivity of aorta taken from rats exposed to nicotine during prenatal (starting by the mating period) and postnatal periods (6 weeks after delivery), or by determining the protein expression of nitric oxide synthase (NOS) enzymes, NADPH oxidase (Nox) and nitrotyrosine. Chronic nicotine exposure at 6 mg/L in drinking water produced a significant decrease in phenylephrine contractility of thoracic aortic rings compared to control and low dose exposure group (0.4 mg/L, p < 0.001). Endothelium-dependent relaxations to acetylcholine increased dose-dependently while no changes were observed in endothelium-independent relaxations to sodium nitroprusside and protein expressions in rat thoracic aorta. It has been concluded that long term nicotine exposure does not have serious effects on endothelial vasodilator response directly and does not change protein expression of NOS or Nox enzymes. However, more studies should be done for the exact mechanisms responsible for the effect of nicotine on endothelial function.

Endogenous flux of nitric oxide: Citrulline is preferred to Arginine.

Both arginine (Arg) and its precursor citrulline (Cit) have received much interest in the past two decades because of their potential effects on whole-body nitric oxide (NO) production and augmentation of NO-dependent signalling pathways. However, the usefulness of Arg supplementation for NO production is questionable because of its high splanchnic first pass metabolism (FPM), which limits its systemic availability. Both hepatic- and extrahepatic arginases critically limit the availability of Arg for the NO synthase enzymes (NOSs) and therefore, a limited amount of oral Arg can reach the systemic circulation for NO synthesis. Arg also has some undesired effects including induction of arginase activity, an increase of urea levels, a decrease of cellular uptake of Cit and decrease of recycling of Arg from Cit. In contrast, Cit has more availability as an NO precursor because of its high intestinal absorption, low FPM and high renal reabsorption. At the cellular level, co-localization of Cit transport systems and the enzymes involved in the Cit-Arg-NO pathway facilitates channelling of Cit into NO. Furthermore, cells preferably use Cit rather than either intra- or extracellular Arg to improve NO output, especially in high-demand situations. In conclusion, available evidence strongly supports the concept that Cit leads to higher NO production and suggests that Cit may have a better therapeutic effect than Arg for NO-disrupted conditions.

The role of extracellular matrix in tumour angiogenesis: the throne has NOx servants.

The extracellular matrix (ECM) dynamics in tumour tissue are deregulated compared to the ECM in healthy tissue along with disorganized architecture and irregular behaviour of the residing cells. Nitric oxide (NO) as a pleiotropic molecule exerts different effects on the components of the ECM driving or inhibiting augmented angiogenesis and tumour progression and tumour cell proliferation and metastasis. These effects rely on the concentration of NO within the tumour tissue, the nature of the surrounding microenvironment and the sensitivity of resident cells to NO. In this review article, we summarize the recent findings on the correlation between the levels of NO and the ECM components towards the modulation of tumour angiogenesis in different types of cancers. These are discussed principally in the context of how NO modulates the expression of ECM proteins resulting in either the promotion or inhibition of tumour growth via tumour angiogenesis. Furthermore, the regulatory effects of individual ECM components on the expression of the NO synthase enzymes and NO production were reviewed. These findings support the current efforts for developing effective therapeutics for cancers.