Biochemical, Pharmacological and Clinical Aspects of Nitric Oxide B.

N2 - Background: The L-arginine/nitric oxide pathway plays a key role in the regulation of arterial tone. Biosynthesis of nitric oxide requires activation of nitric oxide synthase in the presence of tetrahydrobiopterin as a cofactor. Biochemical studies demonstrated that activation of purified nitric oxide synthase at suboptimal concentrations of tetrahydrobiopterin leads to production of hydrogen peroxide. The present experiments were designed to determine whether in coronary arteries inhibition of tetrahydrobiopterin synthesis may favor nitric oxide synthase-catalyzed production of hydrogen peroxide. Methods and Results: Primary branches of canine left anterior descending artery were incubated for 6 hours in minimum essential medium in the presence or in the absence of the tetrahydrobiopterin synthesis inhibitor 2,4-diamino-6-hydroxypyrimidine (DAHP; 10-2 mol/L). Arterial rings were suspended for isometric tension recording. Production of cGMP was measured by radioimmunoassay. Experiments were performed in the presence of indomethacin (10-5 mol/L). During contractions to the thromboxane A2/prostaglandin H2 receptor agonist U46619 (10-7 mol/L), calcium ionophore A23187 (10-9 to 10-6 mol/L) caused endothelium-dependent relaxations. A nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (3 x 10-4 mol/L), significantly inhibited these relaxations. In DAHP-treated arteries, relaxations to A23187 and its stimulating effect on cGMP production were significantly reduced in the presence of catalase (1200 U/mL). By contrast, catalase did not exert any effect in rings incubated in the absence of DAHP. Furthermore, the inhibitory effect of catalase on A23187-induced relaxations was abolished when coronary arteries were incubated in the presence of DAHP plus a liposoluble analogue of tetrahydrobiopterin, 6-methyltetrahydropterin (10-4 mol/L). Conclusions: The present study suggests that hydrogen peroxide may be a mediator of endothelium-dependent relaxations in coronary arteries depleted of tetrahydrobiopterin. This initially compensatory response, triggered by a dysfunctional nitric oxide synthase, may represent an important mechanism underlying oxidative vascular injury.

In 1992 Science named Nitric Oxide (NO) Molecule of the Year.

T1 - Systemic and fetal-maternal nitric oxide synthesis in normal pregnancy and pre-eclampsia

Synthesis of Nitric Oxide - University of Reading

Drought is one of the most important abiotic stresses that causes significant reductions in crop yield and thus hinders the food security. Upon exposure to , plants exhibit a wide range of responses at the whole plant, cellular and molecular levels (; ; ). The NO-synthesizing activity in wheat plants was found to increase under drought conditions. The newly synthesized NO together with H2O2 participated in the regulation of ABA-induced closing of stomata in various plant species (). In addition, the protective role of NO in drought-stressed plants has been reported by several researchers. In a recent work, the activity of NOS in the cytosolic and microsomal fractions of maize leaves was determined (). The results showed that water stress induced increases in NOS activity in the cytosolic and microsomal fractions and the NOS activity in the microsomal fraction was higher and more susceptible to water stress treatment than that in the cytosolic fraction of maize leaves. It was observed that exogenously applied NO, reduced water loss from detached wheat leaves and seedlings subjected to drought conditions, decreased ion leakage and transpiration rate and induced stomatal closure, thereby enhancing plant tolerance to (). Interestingly, a specific NO scavenger, cPTIO, reverted the above actions of NO (). Results of this experiment suggest that exogenous application of NO donors might confer on plants an increased tolerance to severe conditions. It was shown that treatment of plants with exogenous NO enhanced drought tolerance of cut leaves and seedlings of wheat (). In addition, NO treatment enhanced wheat seedling growth and maintained relatively high water content and alleviated oxidative damage (). However, higher dose (2 mM SNP) aggravated the stress as a result of uncontrolled generation of ROS and ineffectiveness of antioxidant systems. Exogenous NO increased the activities of water stress induced subcellular antioxidant enzymes, which decreased accumulation of H2O2. These results suggest that NOS and NR are involved in water stress-induced NO production and NOS is the major source of NO. The potential ability of NO to scavenge H2O2 is at least in part due to the induction of a subcellular antioxidant defense mechanism. NO alleviates the ROS-mediated cytotoxic process in potato leaves (). The ROS-mediated damages caused by drought, including cell death, ion leakage and DNA fragmentation, were inhibited by exogenous NO and all of the protective effects were abolished by the treatment with PTIO (). The protective effect of NO in osmotic stress was recently confirmed in two ecotypes of reed suspension cultures. suggested that polyethylene glycol (PEG-6000) induced NO release in stress-tolerant but not sensitive ecotype reed, effectively protecting against oxidative damage and conferring an increased tolerance to osmotic stress (). In wheat seedlings, the osmotic stress produced by treatment with 0.4 M manitol reduced leaf water loss while increasing the leaf ABA content. These effects were partially reversed by NO scavengers and NOS activity inhibitors (). In tomato detached leaves, the application of NO donors inhibited the synthesis of proteinase inhibitor I and the generation of H2O2 in response to mechanical wounding ().

05/01/2018 · Synthesis of Nitric Oxide

Brief contents Chemistry and biochemistry of nitric oxide, Pharmacology of drug development, Nitric oxide and the respiratory and cardiovascular systems, Nitric oxide and brain functions, Subject index, Author index.

T1 - Tetrahydrobiopterin and dysfunction of endothelial nitric oxide synthase in coronary arteries

effect of Ca 2+ on nitric oxide synthase in the ..

Crane BR, Arvai AS, Ghosh DK, et al. (1998) Structure of nitric oxide synthase oxygenase dimer with pterin and substrate. Science 279: 2121–2126.

03/02/2011 · Biochemistry of Nitric Oxide

Structural modifications of nonsteroidal anti-inflammatory drugs (NSAIDs) have successfully reduced the side effect of gastrointestinal ulceration without affecting anti-inflammatory activity, but they may increase the risk of myocardial infarction with chronic use. The fact that nitroxyl (HNO) reduces platelet aggregation, preconditions against myocardial infarction, and enhances contractility led us to synthesize a diazeniumdiolate-based HNO-releasing aspirin and to compare it to an NO-releasing analogue. Here, the decomposition mechanisms are described for these compounds. In addition to protection against stomach ulceration, these prodrugs exhibited significantly enhanced cytotoxcity compared to either aspirin or the parent diazeniumdiolate toward nonsmall cell lung carcinoma cells (A549), but they were not appreciably toxic toward endothelial cells (HUVECs). The HNO-NSAID prodrug inhibited cylcooxgenase-2 and glyceraldehyde 3-phosphate dehydrogenase activity and triggered significant sarcomere shortening on murine ventricular myocytes compared to control. Together, these anti-inflammatory, antineoplasic, and contractile properties suggest the potential of HNO-NSAIDs in the treatment of inflammation, cancer, or heart failure.

Nitric Oxide Synthesis and Function

AB - Background: The L-arginine/nitric oxide pathway plays a key role in the regulation of arterial tone. Biosynthesis of nitric oxide requires activation of nitric oxide synthase in the presence of tetrahydrobiopterin as a cofactor. Biochemical studies demonstrated that activation of purified nitric oxide synthase at suboptimal concentrations of tetrahydrobiopterin leads to production of hydrogen peroxide. The present experiments were designed to determine whether in coronary arteries inhibition of tetrahydrobiopterin synthesis may favor nitric oxide synthase-catalyzed production of hydrogen peroxide. Methods and Results: Primary branches of canine left anterior descending artery were incubated for 6 hours in minimum essential medium in the presence or in the absence of the tetrahydrobiopterin synthesis inhibitor 2,4-diamino-6-hydroxypyrimidine (DAHP; 10-2 mol/L). Arterial rings were suspended for isometric tension recording. Production of cGMP was measured by radioimmunoassay. Experiments were performed in the presence of indomethacin (10-5 mol/L). During contractions to the thromboxane A2/prostaglandin H2 receptor agonist U46619 (10-7 mol/L), calcium ionophore A23187 (10-9 to 10-6 mol/L) caused endothelium-dependent relaxations. A nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester (3 x 10-4 mol/L), significantly inhibited these relaxations. In DAHP-treated arteries, relaxations to A23187 and its stimulating effect on cGMP production were significantly reduced in the presence of catalase (1200 U/mL). By contrast, catalase did not exert any effect in rings incubated in the absence of DAHP. Furthermore, the inhibitory effect of catalase on A23187-induced relaxations was abolished when coronary arteries were incubated in the presence of DAHP plus a liposoluble analogue of tetrahydrobiopterin, 6-methyltetrahydropterin (10-4 mol/L). Conclusions: The present study suggests that hydrogen peroxide may be a mediator of endothelium-dependent relaxations in coronary arteries depleted of tetrahydrobiopterin. This initially compensatory response, triggered by a dysfunctional nitric oxide synthase, may represent an important mechanism underlying oxidative vascular injury.