Nitric oxide: therapeutic opportunities

Fifteen years after the discovery of nitric oxide as a biological mediator how close are new therapies? This article describes the roles of nitric oxide, illustrates how its discovery is altering the way in which certain established drugs are being used and reviews new therapeutic developments.     

Nitric oxide in vascular biology

Summary.  Nitric oxide is a highly versatile heterodiatomic molecule that effects a variety of actions in the vasculture. Originally identified as a principal determination of vascular tone, nitric oxide has since been recognized to exert anti thrombotic, antiproliferative, and anti-inflammatory effects in the vasculture. At higher concentrations and in the setting of other oxidants, nitric oxide can promote vascular pathology. In this review, we summarize the molecular mechanisms of nitric oxides actions in vascular biology and pathology.     

Nitric oxide synthase gene therapy: progress and prospects

NOS gene therapy has been the focus of extensive research as dysfunction of this enzyme has been implicated in several cardiovascular diseases. Research has concentrated on comparing the effect of gene delivery of NOS isoforms (eNOS, iNOS and nNOS) in healthy and diseased animal models on intimal hyperplasia, restenosis, vascular tone and ischemia-reperfusion injury. Most results demonstrate therapeutic benefits following vascular gene delivery of all NOS in pre-clinical models of cardiovascular disease. eNOS has been shown to have particular promise as it promotes re-endothelialisation and inhibits intimal hyperplasia in injured blood vessels. The ultimate goal is to translate the benefit of NOS gene therapy in animal models into clinical practise. To develop NOS gene therapy for clinical use further work needs to be undertaken to improve delivery systems and vectors to minimise detrimental side-effects and enhance positive treatment outcomes. This review focuses on current research on NOS gene therapy in cardiovascular disease and identifies the next steps that would be necessary to lead to clinical trials.     

Nitric oxide in the human uterine cervix: Endogenous ripening factor

The human uterine cervix can produce nitric oxide (NO), a free radical with an ultra‐short half‐life. The release of NO changes during pregnancy and is increased in early nonviable pregnancies compared to normal uncomplicated pregnancies. This review concentrates on the role of NO release in cervical ripening in pregnant women. Also some suggestions on future aspects are discussed.     

Nitric oxide specifically inhibits integrin‐mediated platelet adhesion and spreading on collagen

Summary. Background: Nitric oxide (NO) inhibits platelet adhesion to collagen, although the precise molecular mechanisms underlying this process are unclear. Objectives: Collagen‐mediated adhesion is a multifaceted event requiring multiple receptors and platelet‐derived soluble agonists. We investigated the influence of NO on these processes. Results: S‐nitrosoglutathione (GSNO) induced a concentration‐dependent inhibition of platelet adhesion to immobilized collagen. Maximal adhesion to collagen required platelet‐derived ADP and TxA₂. GSNO‐mediated inhibition was lost in the presence of apyrase and indomethacin, suggesting that NO reduced the availability of, or signaling by, ADP and TxA₂. Exogenous ADP, but not the TxA₂ analogue U46619, reversed the inhibitory actions of GSNO on adhesion. Under adhesive conditions NO inhibited dense granule secretion but did not influence TxA₂ generation. These data indicated that NO may block signaling by TxA₂ required for dense granule secretion, thereby reducing the availability of ADP. Indeed, we found TxA₂‐mediated activation of PKC was required to drive dense granule secretion, a pathway that was inhibited by NO. Because our data demonstrated that NO only inhibited the activation‐dependent component of adhesion, we investigated the effects of NO on individual collagen receptors. GSNO inhibited platelet adhesion and spreading on α₂β₁ specific peptide ligand GFOGER. In contrast, GSNO did not inhibit GPVI‐mediated adhesion to collagen, or adhesion to the GPVI specific ligand, collagen related peptide (CRP). Conclusions: NO targets activation‐dependent adhesion mediated by α₂β₁, possibly by reducing bioavailability of platelet‐derived ADP, but has no effect on activation‐independent adhesion mediated by GPVI. Thus, NO regulates platelet spreading and stable adhesion to collagen.     

Nitric oxide and nursing: a review

Aims and objectives. This paper, therefore, aimed to review published literature in this area of pharmacological exploitation, to look at the therapeutic applications and clinical relevance and, by so doing, provide an accessible source for nurses to gain insight into the role of nitric oxide in the clinical setting. Background. Nitric oxide is a chemical mediator fundamental in the maintenance of adequate tissue perfusion and effective cardiovascular function; a major endogenous regulator of vascular tone. The use of nitrates are well established as pharmacological agents but it is only recently that it has been recognized that they act as a source of nitric oxide. Although widely addressed within the medical literature, there appears to be a paucity of nursing literature that explores either its physiological action, or its relevance to nursing practice. Conclusions. This literature review provides an overview of the use of nitric oxide and its implications for nursing practice and patient outcomes. Relevance to clinical practice. Knowledge of nitric oxide and its action is pertinent to nurses across diverse specialities. It helps in understanding the principles of many nitrogen‐derived medications which nurses administer to their patients on a daily basis. In terms of oral medication, this is demonstrated by greater insights into the action of nitrates, the appreciation of surprising developments in medications such as sildenafil and the development of new drug opportunities such as nitric oxide–non‐steroidal anti‐inflammatory drugs. Equally, the use of inhaled nitric oxide therapy in adult and neonatal critical care units appears to be an increasingly valuable source of treatment. A particular research challenge is found in the attempt at nitric oxide inhibition in the management of septic shock. The authors argue that understanding such esoteric areas of therapeutic developments is increasingly to be part of the repertoire of knowledge and skills for nurses in the 21st century.     

Nitric oxide: an ubiquitous messenger

Summary— During the last decade, a multitude of experimental arguments have led to the concept that EDRF is nitric oxide (NO), a messenger not only involved in the control of vasomotor tone but also in vascular homeostasis, neuronal and immunological functions. Regardless of its origin, endogenous NO is produced through the conversion of L-arginine to L-citrulline by NO-synthase (NOS) from which several isoforms have recently been isolated, purified and cloned. NOS-type I (isolated from brain) and type III (isolated from endothelial cells) are termed “constitutive-NOS” and produce picomolar levels of NO from which only a small fraction elicits physiological responses. These isoforms are regulated by Ca²⁺-calmodulin with NADPH, FAD/FMN and tetrahydrobiopterin as co-factors and reveal a high degree of homology with the amino-acid sequence of cytochrome P450 reductase within the C-terminal domain. Functionally, neuronal-NOS type I is important in neurotransmission (modulation of NMDA receptor), the central control of vascular homeostasis and possibly learning and memory. In the peripheral nervous system, NOS appears to be linked to nonadrenergic noncho-linergic (NANC) neuronal pathways. Endothelial-NOS type III is essential for the control of vascular tone in response to the release of endogenous mediators, although shear stress is the major trigger of endothelial-NOS activity under physiological conditions. NOS-type III also contributes to the prevention of abnormal platelet aggregation. NOS-types II and IV (isolated from macrophages) are Ca²⁺-calmodulin independent and are termed “inducible-NOS” since their activation is only promoted under pathophysiological situations where macrophages exert cytotoxic effects in response to cytokines. In contrast with NOS-types I and III, activation of NOS-type II in these cells induces the formation of nanomolar levels of NO which act as a defense mechanism of the immune system. Dysfunctions of the L-arginine-NO pathway have been characterized in multiple diseases (atherosclerosis, hypertension, diabete, sepsis, cerebral ischemia, etc) and the design of more selective activators/inhibitors of NOS isoforms is a new challenge for the understanding of their pathophysiology and treatment.     

Nitric oxide and blood: a review

Nitric oxide (NO) was identified as a physiological mediator of vascular tone in 1987. NO produced by endothelial cells causes vasodilatation and also inhibits platelet aggregation and leucocyte adhesion. Red cells metabolize NO to nitrate but may possibly carry and release, or even produce, NO in hypoxic conditions. NO physiology may have important implications for transfusion medicine, ranging from adverse effects of haemoglobin substitutes to preservation of stored platelets and to detrimental effects of stored red cells.     

Nitric oxide and endothelial cellular senescence

Cellular senescence is characterized by permanent exit from the cell cycle and the appearance of distinct morphological and functional changes associated with an impairment of cellular homeostasis. Many studies support the occurrence of vascular endothelial cell senescence in vivo, and the senescent phenotype of endothelial cells can be transformed from anti-atherosclerotic to pro-atherosclerotic. Thus, endothelial cell senescence promotes endothelial dysfunction and may contribute to the pathogenesis of age-associated vascular disorders. Emerging evidence suggests that increasing nitric oxide (NO) bioavailability or endothelial NO synthase (eNOS) activity activates telomerase and delays endothelial cell senescence. In this review, we discuss the potential mechanisms underlying the ability of NO to prevent endothelial cell senescence and describe the possible changes in the NO-mediated anti-senescence effect under pathophysiological conditions, including oxidative stress and hyperglycemia. Further understanding of the mechanisms underlying the anti-senescence effect of NO in endothelial cells will provide insights into the potential of eNOS-based anti-senescence therapy for age-associated vascular disorders.     

Effect of sympathetic stimulation and intrarenal alpha-blockade on the secretion of renin by the human kidney

This study was initiated to explore the possible involvement of renal alpha-adrenoceptors in the regulation of active and inactive renin. In fifteen hypertensive patients who proved not to have vascular abnormalities on diagnostic renal arteriography, blood samples were collected simultaneously from the renal artery and vein before and during an intrarenal infusion of either saline (n = 5), or the alpha-1 blocker doxazosin (n = 5) or the non-selective alpha-1 blocker doxazosin (n = 5) or the non-selective alpha-blocker phentolamine (n = 5). Subsequently, responses of renal blood flow and renin secretion were assessed following 3 min of handgrip exercise. In none of the experiments secretion of inactive renin could be detected. Release of active renin increased from 580 (SEM 170) to 650 (SEM 220) microU min-1 (100 g)-1 during infusion of doxazosin (P less than 0.05) and from 760 (SEM 100) to 1000 (SEM 340) microU min-1 (100 g)-1 during infusion of phentolamine (P less than 0.01). Saline infusion had no effect on secretion of active renin. While handgrip exercise had no significant effect on active renin secretion in the saline and in the doxazosin group, it enhanced secretion from 1000 (SEM 340) to 1280 (SEM 390) microU min-1 (100 g)-1 in the phentolamine group (P less than 0.01). The results indicate that mainly alpha-2 adrenoceptors exert an inhibitory effect on release of active renin, although alpha-1 receptors participate to some degree. There is no evidence that the kidney secretes inactive renin.     

Nitric oxide and its relationship to thrombotic disorders

Summary.  Nitric oxide (NO) is released by the endothelium preventing platelet adhesion to the vessel wall. When released by platelets, NO inhibits further recruitment of platelets to a growing thrombus. Modulation of endogenous NO release may be a mechanism by which the thrombotic response can be regulated as suggested by several clinical diseases associated with impaired bioactive NO. Diseases including atrial fibrillation and coronary atherothrombotic disease have been associated with impaired NO release or decrease in NO bioavailability.     

高血糖大鼠海马CA1区一氧化氮合成酶阳性神经元变化的研究

Nitricoxide（NO）isanewneurotransmitter，existsincentralnervoussystemwidelyandtakespartinnerveconductionandreg－ulationofcerebralbloodstream犤１犦．Butthechangeofnitricoxidesynthetase（NOS）positiveneuronshasn＇tbeenreportedindetail．WeadopthistochemicalmethodtoobserveNOSpositiveneuronsinhippocampusCA１ofratswithhyperglycemia．１Materialsandmethods１．１GroupsandanimalmodelsDivide４０Wistarratsweighted２００～２５０ginto３groups．Normalcontrolgroup（NC）：２０rats．Hyperglycemiagroup（D…     

Nitric oxide synthase inhibition in the histamine headache model

Histamine has been widely used experimentally to induce headache in healthy subjects and migraine in migraineurs. There is evidence that the vascular effects of histamine are at least partially mediated by nitric oxide (NO). Hence we hypothesized that subjective symptoms and hemodynamic effects of histamine could be reduced by systemic NO-synthase inhibition. We therefore studied the effect of pretreatment with N-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of NO-synthase, or placebo on headache, flush and discomfort scores during histamine infusion. Additionally, blood flow velocities in the middle cerebral and the ophthalmic artery and ocular fundus pulsations were measured. Whereas L-NMMA blunted the effect of histamine in the ophthalmic artery and the ocular circulation, NO-synthase inhibition did not mitigate subjective symptoms. Histamine did not affect mean blood flow velocities in the middle cerebral artery. Hence, we conclude that NO-synthase inhibition reduces the histamine-induced vascular effects in the ocular circulation, but is not sufficient to attenuate or abort the subjective symptoms provoked by histamine infusion.     

Nitric oxide, a double edged sword in cancer biology: searching for therapeutic opportunities

Nitric oxide (NO) is a pleiotropic molecule critical to a number of physiological and pathological processes. The last decade has witnessed major advances in dissecting NO biology and its role in cancer pathogenesis. However, the complexity of the interactions between different levels of NO and several aspects of tumor development/progression has led to apparently conflicting findings. Furthermore, both anti-NO and NO-based anticancer strategies appear effective in several preclinical models. This paradoxical dichotomy is leaving investigators with a double challenge: to determine the net impact of NO on cancer behavior and to define the therapeutic role of NO-centered anticancer strategies. Only a comprehensive and dynamic view of the cascade of molecular and cellular events underlying tumor biology and affected by NO will allow investigators to exploit the potential antitumor properties of drugs interfering with NO metabolism. Available data suggest that NO should be considered neither a universal target nor a magic bullet, but rather a signal transducer to be modulated according to the molecular makeup of each individual cancer and the interplay with conventional antineoplastic agents.     

Nitric oxide concentration in the gas phase of the gastrointestinal tract in man

Nitric oxide (NO) has been implicated in various aspects of physiological regulation in the gastrointestinal tract. Hence, measurement of luminal NO concentrations is of interest for studying physiological and pathophysiological alterations in NO generation; however, at present, no reliable measurement techniques are available. Here we describe novel approaches for measurement of NO concentrations directly in the gas phase of the stomach and colon in healthy subjects and patients. Studies were conducted in young healthy volunteers ( n  = 13), intensive care patients ( n  = 8) and patients undergoing gastroscopy ( n  = 8) or colonoscopy ( n  = 8). NO concentrations were measured by chemolumininescence detection in air obtained through a nasogastric tube, after inflation into the stomach of a defined volume of air, or directly in the air suctioned from the endoscope. The mean NO concentration obtained from the stomach of healthy volunteers studied under baseline conditions was 18.0 ± 2.8 (SEM) p.p.m. Day-to-day reproducibility of NO measurements was high. Tube feeding with a nitrite- and nitrate-free feeding solution left gastric NO concentrations unchanged, but standardized bicycle exercise caused an ≈30% decrease in NO levels. NO concentrations in intensive care patients were ≈2 log cycles lower than in healthy volunteers. NO levels in the colon were similar to those in the stomach. We have described two readily applicable techniques for direct, uncontaminated measurement of NO concentrations in the lumen of the gastrointestinal tract. Our finding of a striking reduction in gastric NO concentrations in intensive care patients requires further study.     

抑郁症患者血清一氧化氮及一氧化氮合成酶的检测及其临床研究

目的 探讨血清NO、一氧化氮合成酶(NOS)活力与抑郁症的关系.方法 纳入136例符合中国精神障碍分类与诊断标准的抑郁症患者(实验组)和120名健康志愿者(对照组),进行血清NO水平及NOS活力的检测,并进行对照分析.结果 实验组血清NO水平(70.05±10.34)μmol/L及NOS活力平均水平(29.49±5.12)U/L均高于正常对照组[(67.17±16.52)μmol/L、(26.99±2.87)U/L],差异均有统计学意义(P均<0.05);抑郁症患者中服药组血清NO水平(74.42±8.80)μmol/L及NOS活力平均水平(27.71±5.46)U/L均低于未服药组[(78.81±12.28)μmoL/L、(30.49±4.65)U/L],两者相比,差异有统计学意义(P均<0.05).结论 抑郁症患者血清NO水平及NOS活力升高,NO升高可能是抑郁症发病的影响因素;抗抑郁药可能通过降低血清NO水平而起到抗抑郁作用.     

Importance of renin in blood pressure regulation and therapeutic potential of renin inhibition

Despite improvements in its detection and treatment, hypertension remains a significant public health problem worldwide. In recent years, many international hypertension societies and organisations have set increasingly rigorous blood pressure (BP) targets, with the aim of reducing cardiovascular complications, and this has in turn necessitated the use of more antihypertensive medications to reach these targets in individual patients. There is therefore an ongoing need to develop antihypertensive drugs with new mechanisms of action. Renin inhibitors represent a novel class of compounds which offer considerable promise as BP-lowering agents. Here, we review the rationale for renin inhibition as a therapeutic target and examine the preclinical and clinical evidence for the antihypertensive effectiveness of the renin inhibitors.     

Nitric oxide synthase inhibition: a new principle in the treatment of migraine attacks

Glyceryl trinitrate, an exogenous nitric oxide (NO) donor, and histamine, which causes NO formation in vascular endothelium, have been shown to trigger migraine attacks. However, it remains uncertain whether NO is involved in the subsequent phase of migraine attacks. To answer this question we studied the effect of L-NGmethylarginine hydrochloride (546C88), a NO-synthase inhibitor, on spontaneous migraine attacks. In a double-blind study design, 18 patients with migraine without aura randomly received 546C88 (6 mg/kg) or placebo (5% dextrose) iv given over 15 mm for a single migraine attack (546C88 placebo, 15:3). Furthermore, 11 placebo-treated patients from previous double-blind trials with almost identical design were added to the placebo group in the statistical evaluation. Two hours after the infusion, 10 of 15 L -N^Gmethylarginine hydrochloride-treated patients experienced headache relief compared to 2 of 14 placebo-treated patients ( p =0.0l). Symptoms such as phono- and photophobia were also significantly improved. A similar trend for nausea was not significant. We conclude that NO may be involved in the pain mechanisms throughout the course of spontaneous migraine attacks.     

Nitric Oxide-based Possibilities for Pharmacotherapy

The goal of nitric oxide (NO) based pharmacotherapy is to reach proper homeostasis of NO metabolism in the target tissue where endogenous production of NO is either too weak or excessively increased. In addition to the classic NO-based therapy of cardiovascular conditions with nitrates, a variety of new therapeutic possibilities have emerged including sexual disorders, gastrointestinal system, immunology, tumour growth regulation and respiratory disorders. NO levels of target tissues can be affected directly by NO donors, or indirectly by increasing the level of L-arginine, a substrate of nitric oxide synthase (NOS). While increased production of NO by induceable NOS (iNOS) by, for example, cytokines does not at present seem therapeutically meaningful, increased NO production by constitutive NOS (cNOS) may be involved in the beneficial effects of ACE inhibitors or oestrogens. NO production may be pharmacologically decreased by inhibition of expression of iNOS by glucocorticoids while both cNOS and iNOS derived NO production is inhibited by administration of false substrates, for example L-NAME. Additionally, the respiratory system and related vessels can be reached directly and more selectively by inhalation of pure NO gas. Possible problems in administering NO and perhaps some NO-donors include the toxic nature of the compound itself whereby vital enzyme systems may be inhibited and tissue damaging radicals formed. Future prospects of NO-based pharmocotherapy may feature selective ligands to different NOS isoforms and tissue selective donors that release NO in a controlled fashion.     

Nitric oxide synthase inhibitors appear to improve wound healing in endotoxemic rats: An investigator-blinded, controlled, experimental study

Background:

Although inflammation is a normal part of wound healing, if the inflammatory response is excessive the repair process might be prolonged. Nitric oxide (NO) has been implicated in healing inflammation and wounds.

Objective:

Endotoxins and cytokines associated with sepsis induce NO synthesis in the tissues. This study used tensile strength and tissue hydroxyproline levels as proxies for wound healing to determine whether wound healing in the presence of endotoxemia is improved when NO synthase is inhibited by N-nitro-l-arginine methyl ester (L-NAME) or N⁵-(1-Imino-methyl)-l-ornithine (L-NIO).

Methods:

In this investigator-blinded, controlled, experimental study, male Wistar albino rats (275-300 g) were divided into 4 groups. The first group received an intraperitoneal (IP) injection of Escherichia coli endotoxin 10 mg/kg and an SC injection of 0.9% sodium cloride (NaCl). The second group received IP E coli 10 mg/kg and SC L-NAME 2 mg/kg. The third group received IP E coli 10 mg/kg and L-NIO 10 mg/kg. The control group was administered an IP and an SC injection of 0.9% NaCl. Each group received both injections at 24 and 16 hours before surgery. All rats underwent a 3-cm dorsal midline incision, which was subsequently closed. Five days after surgery, all rats were euthanized and skin from the healing wound was excised. Hydroxyproline levels and tensile strength were then measured.

Results:

Forty-four male rats (mean age, 16 weeks; mean [SD] weight, 284 [16] g) were included in the study. Each of the groups receiving endotoxin (endotoxin, L-NAME, and L-NIO groups) had 12 rats; the control group consisted of 8 rats. All the groups that received endotoxin showed significant declines in hydroxyproline levels versus controls (P < 0.001, P = 0.001, and P = 0.002, respectively). Compared with the control group, the endotoxin-only group had a significant reduction in both mean (SD) hydroxyproline levels and mean (SD) wound tensile strength (298.27 [17.66] vs 175.82 [18.73] g/cm2 and 7.16 [0.51] vs 4.01 [0.29] μg/mg wet tissue; both, P < 0.001). Compared with the endotoxin- only group, rats that received L-NIO had significantly greater mean (SD) hydroxyproline levels and mean (SD) wound tensile strength (6.44 [0.34] vs 4.01 [0.29] μg/mg wet tissue and 280.12 [14.38] vs 175.82 [18.73] g/cm²; both, P < 0.001). Wound tensile strength in the L-NIO group was not significantly different from that in the control group. A significant difference was observed between the L-NIO and L-NAME groups in wound tensile strength (280.12 [14.38] vs 241.38 [20.69] g/cm²; P = 0.001), but not in tissue hydroxyproline levels.

Conclusion:

Inhibition of NO synthesis might improve wound tensile strength, which suggests a possible role for NO inhibitors in improved wound healing in the presence of endotoxemia.