Recent advances in the understanding of the role of nitric oxide in cardiovascular homeostasis

Nitric oxide synthases (NOS) are the enzymes responsible for nitric oxide (NO) generation. To date, 3 distinct NOS isoforms have been identified: neuronal NOS (NOS1), inducible NOS (NOS2), and endothelial NOS (NOS3). Biochemically, NOS consists of a flavin-containing reductase domain, a heme-containing oxygenase domain, and regulatory sites. NOS catalyse an overall 5-electron oxidation of one Nomega-atom of the guanidino group of L-arginine to form NO and L-citrulline. NO exerts a plethora of biological effects in the cardiovascular system. The basal formation of NO in mitochondria by a mitochondrial NOS seems to be one of the main regulators of cellular respiration, mitochondrial transmembrane potential, and transmembrane proton gradient. This review focuses on recent advances in the understanding of the role of enzyme and enzyme-independent NO formation, regulation of NO bioactivity, new aspects of NO on cardiac function and morphology, and the clinical impact and perspectives of these recent advances in our knowledge on NO-related pathways.     

Unresolved roles of platelet nitric oxide synthase.

Endothelial-derived nitric oxide (NO) is a key regulator of platelet function, inhibiting both adhesion to the extracellular matrix and aggregation at sites of vascular injury. Platelets also have the capacity to synthesize and release bioactive NO, which is thought to make a significant contribution to the vascular pool of NO. The regulation of platelet NO production is poorly understood and studies examining the physiological role of platelet-derived NO have produced contradictory and controversial findings. In the present article, we discuss the current understanding of the biochemical and molecular regulation of platelet NO synthesis and outline the potential physiological and clinical significance of this molecule.     

Bench-to-bedside review: Inhaled nitric oxide therapy in adults

Nitric oxide (NO) is an endogenous mediator of vascular tone and host defence. Inhaled nitric oxide (iNO) results in preferential pulmonary vasodilatation and lowers pulmonary vascular resistance. The route of administration delivers NO selectively to ventilated lung units so that its effect augments that of hypoxic pulmonary vasoconstriction and improves oxygenation. This 'Bench-to-bedside' review focuses on the mechanisms of action of iNO and its clinical applications, with emphasis on acute lung injury and the acute respiratory distress syndrome. Developments in our understanding of the cellular and molecular actions of NO may help to explain the hitherto disappointing results of randomised controlled trials of iNO.     

Modulation of pain in osteoarthritis: the role of nitric oxide

BACKGROUND: Patients with osteoarthritis (OA) may experience severe pain, progressive loss of movement function, and disability. Many pain-relieving medications are not effective, and are not able to improve the existing pathology. OBJECTIVES: This review summarizes (1) the pathology, mechanisms of pain production, and conservative management of OA with respect to pain; and (2) explains the role of nitric oxide (NO) in pain reduction and production, especially as related to OA. DISCUSSION: NO is produced in biologic cells by a family of enzymes referred to as the nitric oxide synthases (NOSs). The beneficial or harmful effects of different isoforms, constitutive NOS (cNOS) and inducible NOS (iNOS), respectively, suggest dual effects of NO in biologic structures. The harmful effects of NO are most often reported in the literature. We suggest that (1) NO via the beneficial cNOS pathway is decreased in joint structures exposed to chronic load-induced stresses and biochemical change-induced stresses, (2) monochromatic infrared light energy at an 890 nm wavelength, applied at the skin surface, is absorbed into blood vessels and stimulates production of NO in joints by the beneficial cNOS pathway, (3) NO from the cNOS pathway may help decrease the detrimental effects of NO induced by iNOS and produced in OA pathology, and (4) NO-based intervention may produce substantial pain relief without undesirable side effects by increasing circulation, decreasing nerve irritation, and decreasing inflammation in joints. KEY MESSAGES: (1) The roles of NO in nociception are dual and complex. (2) NO via cNOS, produced transiently in small amounts, can bring dramatic relief to people with painful OA.     

Antitumor actions of ruthenium(III)-based nitric oxide scavengers and nitric oxide synthase inhibitors

The role of endogenous nitric oxide (NO) in the growth and vascularization of a rat carcinosarcoma (P22) has been investigated. Tumor-bearing animals were treated with (i) nitric oxide synthase (NOS) inhibitors, administered via the drinking water, including N(G)-nitro-l-arginine methyl ester (L-NAME), a nonisoform-selective inhibitor, and 2 others that target the inducible (NOS II) enzyme preferentially, namely 1-amino-2-hydroxyguanidine or N-[3-(aminomethyl)benzyl]acetamidine hydrochloride; or (ii) daily injections (intraperitoneally) of 2 Ru(III) polyaminocarboxylates, AMD6221 and AMD6245, both of which are effective NO scavengers. L-NAME, AMD6221, and AMD6245 reduced tumor growth by approximately 60% to 75% of control rates. Tumor sections stained with abs to CD-31/platelet endothelial cell adhesion molecule-1 or NOS III showed that this was associated with a marked reduction (60%-77%) of tumor microvascular densitiy (MVD). Tumors resumed growing promptly when treatment was discontinued, accompanied by partial or complete restoration of MVDs. In contrast, NOS-II selective inhibitors had no effect on tumor growth or vascularization, indicating that both responses require complete blockade of NO production. The results corroborate the view that endogenous NO facilitates tumor development. We suggest that NO deprivation causes tumor feeder vessels to constrict, reducing tumor blood flow. The delivery of oxygen and essential nutrients to the developing tumor is impaired as a consequence, hampering further growth. Normalizing NO levels by withholding treatment causes tumor feeder vessels to dilate, increasing tumor perfusion and reestablishing conditions that allow tumors to begin growing again.     

Role of nitric oxide (NO) in the mechanism of anesthetic action

Published reports on modifications of nitric oxide (NO) synthase (NOS) activity and NO production in the brain during development of anesthesia induced by the most common inhalational (halothane, isoflurane, sevoflurane, enflurane) and intravenous (ketamine, barbiturates, propofol, etomidate) anesthetics are reviewed. According to a popular universally acknowledged hypothesis, inhibition of NOS activity and blockade of NO neurotransmitter function are important steps in the mechanism of action of anesthetics. There are data which confirm the validity of this hypothesis for all above-listed drugs, but there are also data which disagree with it. Some scientists find that anesthesia has no effect on NOS activity and NO production, others found that the enzyme activity and NOS gene expression increased under the effect of anesthesia. Published reports and authors' data on a drastic increase of NO content in the cerebral cortex in halothane anesthesia are discussed. The effects of narcotics on NO-mediated changes in vascular tone are analyzed.     

Direct evidence for the importance of endothelium-derived nitric oxide in vascular remodeling.

The vascular endothelium mediates the ability of blood vessels to alter their architecture in response to hemodynamic changes; however, the specific endothelial-derived factors that are responsible for vascular remodeling are poorly understood. Here we show that endothelial-derived nitric oxide (NO) is a major endothelial-derived mediator controlling vascular remodeling. In response to external carotid artery ligation, mice with targeted disruption of the endothelial nitric oxide synthase gene (eNOS) did not remodel their ipsilateral common carotid arteries whereas wild-type mice did. Rather, the eNOS mutant mice displayed a paradoxical increase in wall thickness accompanied by a hyperplastic response of the arterial wall. These findings demonstrate a critical role for endogenous NO as a negative regulator of vascular smooth muscle proliferation in response to a remodeling stimulus. Furthermore, our data suggests that a primary defect in the NOS/NO pathway can promote abnormal remodeling and may facilitate pathological changes in vessel wall morphology associated with complex diseases such as hypertension and atherosclerosis.     

颅脑损伤后急性期脑脊液中一氧化氮及其合成酶的动态观察

目的：检测一氧化氮（NO）及其合成酶（NOS）在颅脑损伤后急性期脑脊液中的变化,探讨了其临床意义,方法：采用检测NO的中间代谢产物亚硝酸盐来反映NO及放射强度测定法测定NOS活性,分别测定颅脑损伤后急性期脑脊液中NO和NOS变化,并行健康对照,结果：颅脑损伤后NO及NOS脑脊液中浓度第1天即增高,NO第3天达到高峰后开始下降,至第10天仍高于正常对照,NOS于损伤后第1天开始升高,至第10天仍高于正常对照组,结论：NO和NOS参与了颅脑损伤的病理生理过程,动态观察提示NO可能和颅脑损伤病情程度有关。     

Chronic headache and nitric oxide inhibitors

Sensitization of myofascial pain pathways may play an important role in the pathophysiology of chronic headache. Animal studies have shown that sensitization of pain pathways may be caused by associated with activation of neuronal nitric oxide synthase (nNOS) and the generation of nitric oxide (NO). Furthermore, it has been shown that NOS inhibitors reduce central sensitization in animal models of persistent pain. On the basis of these findings, we investigated the analgesic effect of the NOS inhibitor, N-N ^G-methyl arginine hydrochloride, and demonstrated that this drug significantly reduced headache as well as myofascial factors in patients with chronic tension-type headache. In addition, we demonstrated that infusion of the NO donor, glyceryl trinitrate, induces headache in these patients, probably by enhancing the sensitizing effect of pre-existing myofascial input. These studies strongly indicate that NO plays a crucial role in the pathophysiology of tension-type headache. We suggested that the analgesic effect of NOS inhibition in patients with chronic tension-type headache is most likely due to reduction of central sensitization at the level of the spinal dorsal horn or trigeminal nucleus, or both. Furthermore, these data suggest that inhibition of NOS may become a novel means of future treatment of chronic headache. Received: 19 February 2001 / Accepted: 11 April 2001     

Paracrine and autocrine effects of nitric oxide on myocardial function

Complex paracrine interactions exist between endothelial cells and cardiac myocytes in the heart. Cardiac endothelial cells release (or metabolize) several diffusible agents (e.g., nitric oxide [NO], endothelin-1, angiotensin II, adenylpurines) that exert direct effects on myocyte function, independent of changes in coronary flow. Some of these mediators are also generated by cardiac myocytes, often under pathological conditions. This review focuses on the role of NO in this paracrine/autocrine pathway. NO modulates several aspects of "physiological" myocardial function (e.g., excitation-contraction coupling; myocardial relaxation; diastolic function; the Frank-Starling response; heart rate; beta-adrenergic inotropic response; and myocardial energetics and substrate metabolism). The effects of NO are influenced by its cellular and enzymatic source, the amount generated, the presence of reactive oxygen species, interactions with neurohumoral and other stimuli, and the relative activation of cyclic GMP-dependent and -independent signal transduction pathways. The relative physiological importance of endothelium- and myocyte-derived NO remains to be established. In pathological situations (e.g., ischemia-reperfusion, left ventricular hypertrophy, heart failure, transplant vasculopathy and rejection, myocarditis), NO can potentially exert beneficial or deleterious effects. Beneficial effects of NO can result from endothelial-type nitric oxide synthase-derived NO or from spatially and temporally restricted expression of the inducible isoform, inducible-type nitric oxide synthase. Deleterious effects may result from (1) deficiency of NO or (2) excessive production, often inducible-type nitric oxide synthase-derived and usually with concurrent reactive oxygen species production and peroxynitrite formation. The balance between beneficial and deleterious effects of NO is of key importance with respect to its pathophysiological role.     

Biology and chemistry of the inhibition of nitric oxide synthases by pteridine-derivatives as therapeutic agents

Inhibitors of the family of nitric oxide synthases (NOS-I-III; EC 1.14.13.39) are of interest as pharmacological agents to modulate pathologically high nitric oxide (NO) levels in inflammation, sepsis, and stroke. In this article, we discuss the approach for targeting the unique (6R)-5,6,7,8-tetrahydro-L-biopterin (H4Bip) binding site of NOS by appropriate inhibitors. This binding site maximally increases enzyme activity and NO production from the substrate L-arginine upon cofactor binding. The first generation of H4Bip-based NOS inhibitors was based on 4-amino H4Bip derivatives in analogy to anti-folates such as methotrexate. In addition, we discuss the structure-activity relationship of a related series of 4-oxo-pteridine derivatives. Furthermore, molecular modeling studies provide an understanding of pterin antagonism on a structural level based on favorable and unfavorable interactions between protein binding site and ligands. These techniques include 3D-QSAR (CoMFA, CoMSIA) to understand ligand affinity and GRID/consensus principal component analysis (CPCA) to learn about selectivity requirements. Collectively these approaches, in combination with the presented SAR and structural data, provide useful information for the design of novel NOS inhibitors with increased isoform selectivity.     

麻醉犬等长收缩运动中血浆一氧化氮浓度变化及其对血流动力学的影响

目的通过麻醉犬等长收缩运动(IE)中一氧化氮(NO)变化及与注入一氧化氮合成酶(NOS)抑制剂前后IE时心血管指标变化的比较,探讨NO对IE时血流动力学变化的调节作用.方法成年健康杂种犬14只,在安静、IE 3、6、9min,恢复5、10、20min时测定NO及各项血液动力学指标;然后注入NOS抑制剂,重复原试验,测各时间点血流动力学指标.结果IE时NO浓度下降,IE 9min时下降23.6% (P＜0.05),恢复期NO浓度水平逐渐恢复.IE 9min时心率上升明显(P＜0.05)而注入NOS抑制剂后IE 9min时HR下降明显(P＜0.05).收缩压、舒张压及肺毛细血管楔嵌压在注入NOS抑制剂后三者的净增量均高于注入前(P＜0.05).在注入NOS抑制剂后总肺循环阻力、肺动脉阻力、体循环血管阻力均明显上升(P＜0.05).结论急性运动时NO浓度水平下降;NO 不但可以降低外周血管阻力也可降低肺血管阻力,从而减轻IE时的心血管负荷.     

亚低温对大鼠局灶性脑缺血氧自由基和一氧化氮的影响

目的研究亚低温状态下,大鼠急性脑缺血时氧自由基—超氧化物歧化酶（SOD）和一氧化氮（NO）、一氧化氮合酶（NOS）的改变,探讨亚低温对缺血脑组织的保护机制。方法将45只Wistar大鼠随机分为9组,假手术组5只,缺血组及亚低温组又根据缺血、亚低温时间不同分为：3 h2、4 h4、8 h7、2 h亚组（各组均为5只）。采用颈内动脉线栓法制备大鼠大脑中动脉闭塞（MCAO）模型。结果比较缺血组和亚低温组,可见亚低温组栓塞侧脑组织超氧化物歧化酶（SOD）的生成和释放明显增加;亚低温组血清中一氧化氮（NO）、一氧化氮合酶（NOS）的生成和释放明显减少。结论亚低温状态下、氧自由基系统及一氧化氮（NO）、一氧化氮合酶（NOS）的改变,是其保护缺血神经元的重要机制。     

高原红细胞增多症患者血清同型半胱氨酸与一氧化氮、一氧化氮合酶水平的变化

目的探讨高原红细胞增多症(HAPC)患者体内同型半胱氨酸(Hcy)与一氧化氮(NO)、一氧化氮合酶(NOS)水平的关系。方法在海拔3 300 m地区选择HAPC患者和健康人各50例进行血清Hcy、NO含量和NOS活性的检测。结果与健康人比较,HAPC患者血清Hcy水平显著升高(P<0.01),NO含量和NOS活性明显降低(P<0.01);相关分析结果表明,在HAPC患者中血清Hcy水平与NO含量和NOS活性呈显著负相关(r=-0.947、-0.925,P<0.01)。结论血清Hcy水平与NO含量和NOS活性的变化可能与HAPC的发病有关。     

Different roles of nitric oxide synthase isoforms in cardiopulmonary resuscitation in pigs

The purpose of the present study was to identify the roles of the three nitric oxide synthase (NOS) isoforms on whole body ischemia-reperfusion injury during cardiopulmonary resuscitation (CPR) with periodic acceleration (pGz) in pigs. Thirty-two anesthetized pigs (27.6+/-3.4 kg) were monitored for hemodynamics and selected echocardiographic variables. Twenty minutes after NOS inhibition or placebo administration, ventricular fibrillation (VF) was induced and remained untreated for 3 min, followed by CPR with pGz for 15 min, plus 3 min of manual chest compressions and defibrillation attempt. Four groups were studied: (1) saline control; (2) L-NAME (non-selective NOS inhibitor); (3) aminoguanidine (inducible NOS inhibitor); (4) TRIM (neuronal NOS inhibitor). Return of spontaneous circulation (ROSC) to 180 min occurred in 6/8 controls, 4/8 L-NAME, 7/8 aminoguanidine, and 2/8 TRIM animals. The L-NAME group had significantly lower organ blood flow, impaired cardiac function, but higher vascular tone than control group. The aminoguanidine group had the highest organ blood flows and survival rate. Six out of eight TRIM treated animals had initial return of heartbeat; however, with impaired heart contractility and could not survive more than 20 min of ROSC. This study reveals the differential role of endogenous NO produced from the three NOS isoforms during pGz-CPR. Both endothelial and neuronal NOS derived NO show predominantly protective effects while inducible NOS derived NO plays a detrimental role in pGz-CPR. The present study has shown that cardiac arrest and resuscitation appears to be associated with a different expression of NOS isoforms which appear to affect resuscitation outcomes differently.     

一氧化氮合酶抑制剂对严重烧伤大鼠的作用研究

目的 :研究一氧化氮合酶 (NOS)抑制剂对严重烧伤大鼠体内一氧化氮 (NO)含量及 NOS表达的影响及其与预后的关系。方法 :复制大鼠重症烧伤模型 ,检测应用非选择性 NOS抑制剂 N 硝基 L 精氨酸甲酯(L NAME)和选择性诱生型 NOS(i NOS)抑制剂氨基胍 (AG)后大鼠血液中 NO代谢产物 (NO- 2 /NO- 3 )以及肺和十二指肠组织中神经型 NOS(n NOS) m RNA的表达水平 ,同时统计各组大鼠的存活率。结果 :烧伤后大鼠血液中 NO- 2 /NO- 3 含量明显增高 ,L NAME和 AG都能抑制 NO2 /NO- 3 的升高 ,L NAME作用更为明显 ;烧伤后 n NOS的 m RNA表达在肺和十二指肠中均有不同程度升高 ,AG和 L NAME使 n NOS表达增加 ,AG作用更为明显 ;L NAME组动物存活时间较对照组显著缩短 ,AG组动物存活时间明显延长。结论 :结构型NOS(c NOS)与 i NOS在烧伤休克病理生理过程中的作用明显不同 ,i NOS活性过度增高与烧伤休克发病关系密切     

Mitochondrial nitric oxide synthase participates in septic shock myocardial depression by nitric oxide overproduction and mitochondrial permeability transition pore opening

The aim of this study was to determine whether mitochondrial nitric oxide (NO) synthase (NOS) is involved in septic shock myocardial depression. The cecal ligation and puncture (CLP) method was used to induce septic shock. There was a significant depression of hemodynamic parameters recorded in the septic shock stage. After using nonselective NOS inhibitor N-nitro-L-arginine methyl ester (L-NAME), inducible NOS inhibitor aminoguanidine (AMG), and neuronal NOS inhibitor 7-nitroindazole (7-NI), depression of the parameters was partly attenuated. Nitric oxide production in isolated cardiac mitochondria increased obviously in the CLP-septic shock stage, L-NAME and 7-NI both decreased NO production significantly. Nitrite/nitrate (NOx) production in the septic shock stage was much greater than those in the corresponding sham groups, and NOx production in the cytosol by inducible NOS was greater. Treatment with AMG suppressed NOx production in the cytosol by iNOS, whereas treatment with 7-NI decreased NOx production in the mitochondria. Mitochondrial NOS expression increased significantly in the septic shock stage, and its overexpression was attenuated using 7-NI. There was no significant decrease in the mitochondrial permeability transition pore measurement in the CLP-septic shock group, whereas a significant decrease was observed in those treated with L-NAME or 7-NI. These results indicate that overexpression of mitochondrial NOS is involved in myocardial depression.     

八肽缩胆囊素对脂多糖诱导血管内皮细胞诱生型一氧化氮合酶表达变化的抑制作用

目的探讨八肽缩胆囊素（CCK-8）对脂多糖（LPS）诱导血管内皮细胞诱生型一氧化氯合酶（iNOS）表达变化的影响。方法培养人脐静脉内皮细胞株ECV-304细胞。用0．01、0．1和1mg／L LPS处理2～24h，用生理盐水、10mol／LCCK-8和0．1mg／L LPS＋10^-8、10^-7、10^-8mol／L CCK-8处理16h；用比色法检测培养液中一氧化氮（NO）含量、细胞NOS活性，免疫细胞化学及蛋白质免疫印迹法检测iNOS蛋白表达。结果与生理盐水处理的对照组比较，LPS诱导培养液NO含量增多、细胞NOS活性增高、iNOS蛋白表达上调；CCK-8剂量依赣性抑制LPS的上述效应。而单独作用对iNOS蛋白表达、NOS活性和NO含量均无明显影响。结论CCK-8可以明显抑制LPS引起ECV-304细胞iNOS蛋白表达上调。减少NO生成。     

Inducible nitric oxide synthase: Regulation,structure, and inhibition

A considerable number of human diseases have an inflammatory component, and a key mediator of immune activation and inflammation is inducible nitric oxide synthase (iNOS), which produces nitric oxide (NO) from l -arginine. Overexpressed or dysregulated iNOS has been implicated in numerous pathologies including sepsis, cancer, neurodegeneration, and various types of pain. Extensive knowledge has been accumulated about the roles iNOS plays in different tissues and organs. Additionally, X-ray crystal and cryogenic electron microscopy structures have shed new insights on the structure and regulation of this enzyme. Many potent iNOS inhibitors with high selectivity over related NOS isoforms, neuronal NOS, and endothelial NOS, have been discovered, and these drugs have shown promise in animal models of endotoxemia, inflammatory and neuropathic pain, arthritis, and other disorders. A major issue in iNOS inhibitor development is that promising results in animal studies have not translated to humans; there are no iNOS inhibitors approved for human use. In addition to assay limitations, both the dual modalities of iNOS and NO in disease states (ie, protective vs harmful effects) and the different roles and localizations of NOS isoforms create challenges for therapeutic intervention. This review summarizes the structure, function, and regulation of iNOS, with focus on the development of iNOS inhibitors (historical and recent). A better understanding of iNOS’ complex functions is necessary before specific drug candidates can be identified for classical indications such as sepsis, heart failure, and pain; however, newer promising indications for iNOS inhibition, such as depression, neurodegenerative disorders, and epilepsy, have been discovered.     

复发性口疮患者雷公藤多甙治疗前后血清一氧化氮、一氧化氮合酶水平的变化

目的观察复发性口疮(RAU)患者用雷公藤多甙治疗前后血清一氧化氮(NO)、一氧化氮合酶(NOS)水平的变化,为治疗及预后判断提供依据。方法应用硝酸还原酶法对132例经临床确诊的RAU患者治疗前后和60名正常对照者血清NO、NOS水平分别进行检测。结果在治疗前RAU患者血清NO、NOS水平明显高于正常人,经雷公藤多甙治疗症状缓解或消失后,血清NO、NOS下降至正常人水平,RAU患者治疗前后血清中NO、NOS水平差异有显著性(P<0.01)。结论NO、NOS的动态检测对其疗效判断有一定的价值。