Inhibition of constitutive and inducible nitric oxide synthase: potential selective inhibition

The reaction of hydropersulfides (RSSH) with S-nitrosothiols (RS-NO) and the biological/physiological implications

S-Nitrosothiol (RS-NO) generation/levels have been implicated as being important to numerous physiological and pathophysiological processes. As such, the mechanism(s) of their generation and degradation are important factors in determining their biological activity. Along with the effects on the activity of thiol proteins, RS-NOs have also been reported to be reservoirs or storage forms of nitric oxide (NO). That is, it is hypothesized that NO can be released from RS-NO at opportune times to, for example, regulate vascular tone. However, to date there are few established mechanisms that can account for facile NO release from RS-NO. Recent discovery of the biological formation and prevalence of hydropersulfides (RSSH) and their subsequent reaction with RS-NO species provides a possible route for NO release from RS-NO. Herein, it is found that RSSH is capable of reacting with RS-NO to liberate NO and that the analogous reaction using RSH is not nearly as proficient in generating NO. Moreover, computational results support the prevalence of this reaction over other possible competing processes. Finally, results of biological studies of NO-mediated vasorelaxation are consistent with the idea that RS-NO species can be degraded by RSSH to release NO.

Neuroinflammatory Markers: Key Indicators in the Pathology of Neurodegenerative Diseases

Neuroinflammation, a protective response of the central nervous system (CNS), is associated with the pathogenesis of neurodegenerative diseases. The CNS is composed of neurons and glial cells consisting of microglia, oligodendrocytes, and astrocytes. Entry of any foreign pathogen activates the glial cells (astrocytes and microglia) and overactivation of these cells triggers the release of various neuroinflammatory markers (NMs), such as the tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-1β (IL-10), nitric oxide (NO), and cyclooxygenase-2 (COX-2), among others. Various studies have shown the role of neuroinflammatory markers in the occurrence, diagnosis, and treatment of neurodegenerative diseases. These markers also trigger the formation of various other factors responsible for causing several neuronal diseases including Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), multiple sclerosis (MS), ischemia, and several others. This comprehensive review aims to reveal the mechanism of neuroinflammatory markers (NMs), which could cause different neurodegenerative disorders. Important NMs may represent pathophysiologic processes leading to the generation of neurodegenerative diseases. In addition, various molecular alterations related to neurodegenerative diseases are discussed. Identifying these NMs may assist in the early diagnosis and detection of therapeutic targets for treating various neurodegenerative diseases.

Nitric Oxide as a Central Molecule in Hypertension: Focus on the Vasorelaxant Activity of New Nitric Oxide Donors

Cardiovascular diseases include all types of disorders related to the heart or blood vessels. High blood pressure is an important risk factor for cardiac complications and pathological disorders. An increase in circulating angiotensin-II is a potent stimulus for the expression of reactive oxygen species and pro-inflammatory cytokines that activate oxidative stress, perpetuating a deleterious effect in hypertension. Studies demonstrate the capacity of NO to prevent platelet or leukocyte activation and adhesion and inhibition of proliferation, as well as to modulate inflammatory or anti-inflammatory reactions and migration of vascular smooth muscle cells. However, in conditions of low availability of NO, such as during hypertension, these processes are impaired. Currently, there is great interest in the development of compounds capable of releasing NO in a modulated and stable way. Accordingly, compounds containing metal ions coupled to NO are being investigated and are widely recognized as having great relevance in the treatment of different diseases. Therefore, the exogenous administration of NO is an attractive and pharmacological alternative in the study and treatment of hypertension. The present review summarizes the role of nitric oxide in hypertension, focusing on the role of new NO donors, particularly the metal-based drugs and their protagonist activity in vascular function.

The iNOS Activity During an Immune Response Controls the CNS Pathology in Experimental Autoimmune Encephalomyelitis

Inducible nitric oxide synthase (iNOS) plays a critical role in the regulation of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). Previous studies have shown that iNOS plays pathogenic as well as regulatory roles in MS and EAE. However, how does iNOS alters the pathophysiology of the central nervous system (CNS) in neuronal autoimmunity is not clearly understood. In the present work, we show that treatment of mice with L-NAME, an iNOS inhibitor, during the antigen-priming phase primarily alters brain pathology, while in the subsequent effector phase of the immune response, the spinal cord is involved. Inhibition of iNOS during the priming phase of the immune response promotes the infiltration of pathogenic CD11b⁺F4/80^-Gr-1⁺ cells, but there is low recruitment of regulatory CD11b⁺F4/80⁺ cells in the brain. Inhibition of iNOS during the effector phase shows similar pathogenic alterations in the spinal cord, instead of in the brain. Treatment of wild-type mice with L-NAME or mice having genetic deficiency of iNOS show lower MHC-II expression on the dendritic cells, but not on macrophages. Our data suggest that iNOS has a critical regulatory role during antigen-priming as well as in the effector phase of EAE, and inhibition iNOS at different stages of the immune response can differentially alter either the brain or spinal cord pathology. Understanding the cellular and molecular mechanisms through which iNOS functions could help to design a better strategies for the clinical management of neuroinflammation and neuronal autoimmunity.

Effects of nitric oxide modulating activities on development of enteric nervous system mediated gut motility in chick embryo model

The enteric nervous system (ENS) arises from the enteric neural crest-derived cells (ENCCs), and many molecules and biochemical processes may be involved in its development. This study examined the effects of modulating embryonic nitric oxide (NO) activity on the intestinal motility induced by ENS. One-hundred-and-twenty fertilized chicken eggs were assigned to three main groups and incubated at 37 degrees Centigrade and 60 percent humidity. The eggs were treated with NG-nitro-Larginine methyl ester (L-NAME), sodium nitroprusside (SNP), L-arginine (L-Arg) or vehicle from days 3 (1st group), 7 (2nd group) and 10 (3rd group) of incubation and continued up to day 18. On day 19, the embryos were sacrificed, the jejunal and colorectal segments were taken and the intestinal motility was assessed using isolated organ system. The intestinal motility was recorded normally and following cholinergic, adrenergic and non-adrenergic non-cholinergic (NANC) stimulations. The ENS structure was assessed by immunohistochemistry (IHC) using glial fibrillary acidic protein (GFAP). Rhythmic intestinal contractions were seen in all treatment groups, but inhibition of NO in the LNAME- treated embryos caused significant decrease (p less than 0.01) in the frequency and amplitude of the contraction. The responsiveness to adrenergic, cholinergic and NANC stimulations was also significantly decreased (p less than 0.05). The GFAP expression was significantly (p less than 0.05) reduced in the L-NAME-treated embryos. This study showed that the inhibition of NO caused a deficient development of the ENS, leading to a decrease in the frequency and amplitude of the intestinal contractions and reduced the responsiveness to adrenergic, cholinergic and NANC signalling.

Salvianolic acid B exerts vasoprotective effects through the modulation of heme oxygenase-1 and arginase activities

Salvia miltiorrhiza (Danshen), a traditional Chinese herbal medicine, is commonly used for the prevention and treatment of cardiovascular disorders including atherosclerosis. However, the mechanisms responsible for the vasoprotective effects of Danshen remain largely unknown. Salvianolic acid B (Sal B) represents one of the most bioactive compounds that can be extracted from the water-soluble fraction of Danshen. We investigated the effects of Danshen and Sal B on the inflammatory response in murine macrophages. Danshen and Sal B both induced the expression of heme oxygenase-1 (HO-1) and inhibited nitric oxide (NO) production and inducible NO synthase (iNOS) expression in lipopolysaccharide (LPS)-activated RAW 264.7 cells. Inhibition of HO activity using Sn-protoporphyrin-IX (SnPP) abolished the inhibitory effect of Sal B on NO production and iNOS expression. Sal B increased macrophage arginase activity in a dose-dependent manner and diminished LPS-inducible tumor necrosis factor-α production. These effects were also reversed by SnPP. These data suggest that HO-1 expression plays an intermediary role in the anti-inflammatory effects of Sal B. In contrast to the observations in macrophages, Sal B dose-dependently inhibited arginase activity in murine liver, kidney, and vascular tissue. Furthermore, Sal B increased NO production in isolated mouse aortas through the inhibition of arginase activity and reduction of reactive oxygen species production. We conclude that Sal B improves vascular function by inhibiting inflammatory responses and promoting endothelium-dependent vasodilation. Taken together, we suggest that Sal B may represent a potent candidate therapeutic for the treatment of cardiovascular diseases associated with endothelial dysfunction.

Possibility of the regression of atherosclerosis through the prevention of endothelial senescence by the regulation of nitric oxide and free radical scavengers

In the elderly, atherosclerotic diseases such as stroke and myocardial infarction occupy a major part of their causes of death and care. The elderly always have atherosclerosis in their aorta and other arteries and are exposed to risk of attacks. It is the elderly who should receive its safe, harmless and advanced treatment. Advanced stage of atherosclerosis in the elderly is progressed by complicated risk factors such as dyslipidemia and diabetes mellitus and specific risk factors for the elderly, aging (and menopause). Treatment of atherosclerotic disease may need special ones targeted for the elderly. Recent studies reported that frequencies of dyslipidemia were not decreased in the older oldest. In the elderly, impaired glucose tolerance occurs and it progresses atherosclerosis. Endothelial dysfunction like impairment of nitric oxide (NO) bioavailability also progresses atherosclerosis. Although we tried to regress the high cholesterol diet-induced atherosclerosis in rabbit aorta with a normal diet with or without statin, regression could not be achieved. NO targeting gene therapy (adenovirus endothelial nitric oxide synthase [eNOS] gene vector) regressed 20% of atherosclerotic lesions through reduction of lipid contents, however, a more integrated strategy is important for complete regression. We paid attention to NO bioavailability and developed two ways of increasing it in atherosclerosis: citrulline therapy and arginase II inhibition by estrogen. Further, we found a close relation between atherosclerosis and endothelial senescence and that NO can prevent it, especially in a diabetic model. Taken together, regression of atherosclerosis can be achieved by not only regulation of various risk factors but regulation of the cross-talk of NO and free radicals.

Cellular and biochemical actions of melatonin which protect against free radicals: role in neurodegenerative disorders

Molecular oxygen is toxic for anaerobic organisms but it is also obvious that oxygen is poisonous to aerobic organisms as well, since oxygen plays an essential role for inducing molecular damage. Molecular oxygen is a triplet radical in its ground-stage (.O-O.) and has two unpaired electrons that can undergoes consecutive reductions of one electron and generates other more reactive forms of oxygen known as free radicals and reactive oxygen species. These reactants (including superoxide radicals, hydroxyl radicals) possess variable degrees of toxicity. Nitric oxide (NO*) contains one unpaired electron and is, therefore, a radical. NO* is generated in biological tissues by specific nitric oxide synthases and acts as an important biological signal. Excessive nitric oxide production, under pathological conditions, leads to detrimental effects of this molecule on tissues, which can be attributed to its diffusion-limited reaction with superoxide to form the powerful and toxic oxidant, peroxynitrite.Reactive oxygen and nitrogen species are molecular "renegades"; these highly unstable products tend to react rapidly with adjacent molecules, donating, abstracting, or even sharing their outer orbital electron(s). This reaction not only changes the target molecule, but often passes the unpaired electron along to the target, generating a second free radical, which can then go on to react with a new target amplifying their effects.This review describes the mechanisms of oxidative damage and its relationship with the most highly studied neurodegenerative diseases and the roles of melatonin as free radical scavenger and neurocytoskeletal protector.

Effects of acute caffeine administration on NOS and Bax/Bcl2 expression in the myocardium of rat

Caffeine is the most frequently ingested neuroactive drug in the world and it is largely used to delay fatigue and improve physical activity. Caffeine can modulate NO synthesis in cells and may influence muscular function by modifying the cellular cycle life-death. There is little data concerning the relationship between caffeine in the heart, NOS expression and apoptosis and no data regarding the acute effect of high doses of caffeine in the in vivo myocardium. We therefore studied hemodynamic NOS and Bax/Bcl2 expression in the rat myocardium after a single cafffeine administration. Thirty-two male rats were divided into six groups: the first was iv-injected with caffeine (16 mg/kg), the second with caffeine + L-NAME (30 mg/kg), the third with caffeine + L-arg (0.5 g/kg), the fourth with caffeine + L-NAME + L-arg and finally the fifth with saline. Mean arterial blood pressure (MAP) was monitored for 30 min, then the animals were killed. The sixth group was injected with caffeine and killed after 2 h. The hearts were isolated and processed by immunohistochemistry. We found that caffeine increased MAP temporarily while caffeine + L-NAME increased it for a longer period. In the control myocardium, all NOS isoforms were expressed. The Bcl2 were strongly expressed inside the perinuclear cytoplasm whereas Bax was very faintly detectable in the peripheral cytoplasm. In caffeine and caffeine + L-NAME treated animals, NOS expression disappeared. Bax and Bcl2 expression did not vary. The l-arg administration reversed these caffeine and L-NAME effects on NOS expression. Two hours after caffeine, NOS expression increased and Bax and Bcl2 expression did not vary, although Bcl2 was mainly expressed in the peripheral cytoplasm. We conclude that improved caffeine-induced physical performance could also be related to caffeine's ability to interfere with endogenous myocardial NO synthesis. Furthermore, we suggest that myocardial cell plays an effective anti-apoptotic role against acute caffeine administration.

Differential effects of nitric oxide synthase inhibitors on endothelium-dependent and nitrergic nerve-mediated vasodilatation in the bovine ciliary artery

BACKGROUND AND PURPOSE

We have previously demonstrated that L-NMMA (NG-monomethyl-L-arginine) selectively inhibits vasodilatation produced by endothelium-derived nitric oxide but not nitrergic nerves in the bovine penile artery. The present study investigated whether L-NMMA had a similar selective action in the bovine ciliary artery. We also investigated whether two recently introduced inhibitors of neuronal nitric oxide synthase (nNOS), AAAN (N-(4S)-4-amino-5-[aminoethyl]aminopentyl-N'-nitroguanidine) and L-NPA (NG-propyl-L-arginine), produced selective blockade of vasodilatation induced by nitrergic nerves but not endothelium-derived nitric oxide.

EXPERIMENTAL APPROACH

Rings of bovine ciliary artery were suspended in a wire myograph for tension recording. Neurogenic (nitrergic) vasodilatation was elicited by electrical field stimulation, and endothelium-dependent, nitric oxide-mediated dilatation was evoked using bradykinin.

KEY RESULTS

L-NMMA inhibited vasodilatation induced by endothelium-derived nitric oxide but not the nitrergic nerves. In fact, L-NMMA, acted like L-arginine in protecting nitrergic vasodilatation against inhibition by L-NAME (NG-nitro-L-arginine methyl ester). AAAN had no effect on vasodilatation induced by either nitrergic nerves or endothelium-derived nitric oxide, but L-NPA inhibited both with equal potency.

CONCLUSIONS AND IMPLICATIONS

In the bovine ciliary artery, L-NMMA acts as a selective inhibitor of the vasodilatation induced via endothelial NOS, without affecting that operating via nNOS. Furthermore, the putative nNOS inhibitors, AAAN and L-NPA failed to produce the expected selective inhibition of nitrergic vasodilatation in this artery.

Modulating role of estradiol on arginase II expression in hyperlipidemic rabbits as an atheroprotective mechanism

We evaluated the effects of a 0.5% cholesterol-enriched diet (HCD) on nitric-oxide synthase (NOS) and arginase expression and the modulating role of 17beta-estradiol (E(2)) on this phenomenon. Thirty oopherectomized rabbits were divided into three groups and treated for 15 weeks. Group I received normal chow; group II, HCD; and group III, HCD plus E(2) pellets. Animals in group II showed an increase in plasma lipids, and they demonstrated atheromatous lesions as well as expression of arginase I and II accompanied by a significant number of BrdU-positive cells in endothelial cells and intimal muscle cells, suggestive of an increase in cellular proliferation. There was significant expression of inducible NOS and increased staining of nitrotyrosine-positive areas. These were not observed in group I animals. In both groups, E(2) levels were low. In group III animals, E(2) supplementation led to a decrease in atheromatous lesions and BrdU-positive cells and reduced expression of both inducible NOS and arginase I and II accompanied by a decrease in nitrotyrosine staining. E(2) levels were increased. Our results suggest that E(2) was responsible for these effects, despite the animals being hyperlipidemic, similar to those in group II. Because arginase is responsible for cell proliferation by converting l-arginine to polyamines, our results indicate that expression of arginase may play an important role in cellular proliferation in atherosclerosis, and inhibition of arginase expression by E(2) may be another potential mechanism in attenuating atherogenesis.

Potential role of heme oxygenase-1 in the progression of rat adjuvant arthritis

Rat adjuvant arthritis is an experimental model widely used to evaluate etiopathogenetic mechanisms in chronic inflammation. We have examined the participation of heme oxygenase-1 (HO-1) in this experimental arthritis. In this study, an increased nitric oxide (NO) production in the paw preceded the upregulation of HO-1, whereas selective inhibition of inducible NO synthase (iNOS) after the onset of arthritis decreased HO-1 expression, suggesting that the induction of this enzyme may depend on NO produced by iNOS. Therapeutic administration of the HO-1 inhibitor tin protoporphyrin IX was able to control the symptoms of arthritis. This agent significantly decreased leukocyte infiltration, hyperplastic synovitis, erosion of articular cartilage and osteolysis, as well as the production of inflammatory mediators. In this experimental model, HO-1 can be involved in vascular endothelial growth factor production and angiogenesis. These results support a role for HO-1 in mediating the progression of the disease in this model of chronic arthritis.

Inhibition of dimethylarginine dimethylaminohydrolase (DDAH) and arginine deiminase (ADI) by pentafluorophenyl (PFP) sulfonates

A range of pentafluorophenyl (PFP) sulfonate esters derived from the reaction of PFP vinyl sulfonate and various nitrones are shown to have significant inhibitory activity against the bacterial enzymes DDAH and ADI.

Beneficial effects of heme oxygenase-1 up-regulation in the development of experimental inflammation induced by zymosan

Heme oxygenase-1 (HO-1) is part of the integrated response to oxidative stress. This enzyme may exert anti-inflammatory effects in some animal models, although the precise mechanisms are not fully understood. We have examined the role of HO-1 in the inflammatory response induced by zymosan in the mouse air pouch. Zymosan administration induced HO-1 protein expression in leukocytes migrating to exudates, with maximal levels in the late phase of this response (24-48 h). This was accompanied by ferritin induction and bilirubin accumulation, indicating that this enzyme is active in our model. HO-1 expression by zymosan treatment was partly reduced by aminoguanidine, suggesting the participation of endogenous nitric oxide in the mechanisms leading to HO-1 synthesis in the zymosan-injected mouse air pouch. Up-regulation of HO-1 by hemin administration resulted in inhibition of nitric-oxide synthase-2 activity, cellular infiltration into the air pouch exudate, and plasmatic exudation. Leukotriene B4 levels in exudates were significantly decreased in the early phase of this response (4 h), whereas interleukin-1beta and tumor necrosis factor-alpha were inhibited at all time points. Inhibition of HO-1 activity by zinc protoporphyrin IX prevented most of the effects caused by hemin administration. Our results indicate that HO-1 exerts anti-inflammatory effects on the response to zymosan in the mouse air pouch and support a role for this enzyme in the modulation of inflammatory processes.

Sources for superoxide release: lessons from blockade of electron transport, NADPH oxidase, and anion channels in diaphragm

Isolated diaphragm releases low levels of superoxide (O2*-) at rest and much higher levels during heat stress. The molecular source is unknown. The hypothesis was tested that heat stress stimulates mitochondrial complex activity or NADPH oxidases, resulting in increased O2*- release. The mitochondria within intact rat diaphragm were inhibited at complex I (amobarbital or rotenone) or complex I and II (rotenone plus thenoyltrifluoroacetone). NADPH oxidases were blocked by diphenyliodonium. None of these treatments inhibited O2*- release. Conversely, most blockers stimulated O2*- release. As intracellular O2*- generators require a mechanism for O2*- transport across the membrane, anion channel blockers, probenecid and 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid, were also tested. Neither blocker had any inhibitory effect on O2*- release. These results suggest that O2*- released from diaphragm is not directly dependent on mitochondrial complex activity and that it is not a reflection of passive diffusion of O2*- through anion channels. Although the molecular source for extracellular O2*- remains elusive, it is clearly sensitive to temperature and conditions of "chemical hypoxia" induced by partial or complete mitochondrial inhibition.

Nitric oxide, inducible nitric oxide synthase and inflammation in veterinary medicine

Inflammation is a process consisting of a complex of cytological and chemical reactions which occur in and around affected blood vessels and adjacent tissues in response to an injury caused by a physical, chemical or biological insult. Much work has been performed in the past several years investigating inducible nitric oxide synthase (NOS, EC 1.14.13.39) and nitric oxide in inflammation. This has resulted in a rapid increase in knowledge about iNOS and nitric oxide. Nitric oxide formation from inducible NOS is regulated by numerous inflammatory mediators, often with contradictory effects, depending upon the type and duration of the inflammatory insult. Equine medicine appears to have benefited the most from the increased interest in this small, inflammatory mediator. Most of the information on nitric oxide in traditional veterinary species has been produced using models or naturally occurring inflammatory diseases of this species.

Homocysteine stimulates inducible nitric oxide synthase expression in macrophages: antagonizing effect of ginkgolides and bilobalide

Hyperhomocysteinemia is an independent risk factor for atherosclerotic diseases. Inducible nitric oxide synthase (iNOS) is mainly expressed in macrophages upon stimulation. Overproduction of nitric oxide (NO) by iNOS can exacerbate the development of atherosclerosis. Our previous studies demonstrated that the extract of ginkgo biloba leaves (EGb) inhibited the iNOS-mediated NO production in monocyte-derived macrophage. We also reported that homocysteine could stimulate monocyte chemoattractant protein-1 (MCP-1) expression in vascular cells causing enhanced monocyte chemotaxis. The objective of the present study was to investigate the effect of homocysteine on iNOS-mediated NO production in macrophages and the antagonizing effect of EGb. Human monocytic cell (THP-1)-derived macrophages were incubated with homocysteine for various time periods. Homocysteine at concentrations of 0.05-0.1 mM significantly stimulated NO production and iNOS activity in macrophages via increased expression of iNOS mRNA and protein. The increased iNOS expression was associated with activation of nuclear factor-kappa B (NF-kappaB) arising from reduced expression of inhibitor protein (IkappaB alpha) mRNA as well as increased phosphorylation of IkappaB alpha protein in homocysteine-treated cells. EGb and its terpenoids (ginkgolide A, ginkgolide B and bilobalide) could antagonize the homocysteine effect on iNOS expression in macrophages via their antioxidant effect resulting in attenuation of NF-kappaB activation. Taken together, our results have demonstrated that homocysteine, at pathophysiological concentrations, stimulates iNOS-mediated NO production in macrophages. EGb and its terpenoids can antagonize such stimulatory effect via antioxidation and attenuation of NF-kappaB activation.

The first total synthesis of dragmacidin d

The first total synthesis of the biologically significant bis-indole alkaloid dragmacidin D (5) has been achieved. Thermal and electronic modulation provides the key for a series of palladium-catalyzed Suzuki cross-coupling reactions that furnished the core structure of the complex guanidine- and aminoimidazole-containing dragmacidins. Following this crucial sequence, a succession of meticulously controlled final events was developed leading to the completion of the natural product.

The nitric oxide synthase inhibitor NG-Nitro-L-arginine increases basal forebrain acetylcholine release during sleep and wakefulness

Cholinergic neurotransmission in the basal forebrain changes across the sleep/wake cycle, and considerable data show cortical activation by ACh originating from basal forebrain neurons. These findings have stimulated efforts to elucidate molecular modulators of ACh release within the basal forebrain. Basal forebrain cholinergic neurons contain nitric oxide synthase (NOS), the enzyme that produces the gaseous neuromodulator nitric oxide. This study tested the hypothesis that administration of an NOS inhibitor to the basal forebrain would alter basal forebrain ACh release, sleep, and respiratory rate. Seven cats were instrumented for recording sleep and wakefulness and for in vivo microdialysis and microinjection. Compared with Ringer's solution (control), microdialysis delivery of the NOS inhibitor N(G)-nitro-l-arginine (NLA; 10 mm) increased ACh release during wakefulness (33%), non-rapid eye movement (NREM) sleep (70%), and rapid eye movement (REM) sleep (16%). Mean +/- SEM ACh levels (pmol/10 min) during control and NLA dialysis, respectively, were 0.58 +/- 0.03 and 0.77 +/- 0.06 in wakefulness, 0.36 +/- 0.01 and 0.61 +/- 0.06 in NREM sleep, and 0.68 +/- 0.06 and 0.79 +/- 0.09 in REM sleep. Increases in ACh release were not evoked by dialysis delivery of the less active enantiomer N(G)-nitro-d-arginine. Dialysis administration of NLA did not alter respiratory rate. Sleep-dependent changes in basal forebrain ACh release were localized specifically to lateral basal forebrain regions and did not occur in medial basal forebrain sites. Microinjection of NLA into the lateral basal forebrain did not significantly alter the sleep/wake cycle. In contrast to NLA-induced depression of REM sleep and ACh release in the cat pons, the present results demonstrate that NLA increased ACh release in the cat basal forebrain and had no effect on sleep. The different effects of NLA on ACh release in the cat pons and cat basal forebrain may prove relevant for developing compounds that differentially alter cholinergic neurotransmission in specific brain regions.

Medroxyprogesterone acetate does not antagonize estrogen-induced increases in endothelium-dependent vasodilation: potential clinical implications

OBJECTIVE

Determine the effect of combined 17beta-estradiol benzoate (E2) and medroxyprogesterone acetate (MPA) administration on endothelium-dependent vasorelaxation to acetylcholine (ACh).

DESIGN

Prospective, ex vivo study.

SETTING

Academic research laboratory.

ANIMAL(S)

Mature female rats.

INTERVENTION(S)

Ovariectomized rats received one of the following interventions daily for 3 days: [1] corn oil via IM injection, [2] E2 (20 microg/kg IM), or [3] E2 (20 microg/kg IM) and MPA (10 mg/kg IM).

MAIN OUTCOME MEASURE(S)

Basal release of nitric oxide (NO) and endothelium-dependent and endothelium-independent vasodilation from thoracic aortas obtained from each group.

RESULT(S)

Estradiol treatment potentiated the endothelium-dependent relaxation to ACh when compared with the control group. Administration of MPA with E2 did not antagonize the beneficial effect of E2 on endothelium-dependent relaxation. Estradiol treatment alone or in combination with MPA did not affect endothelium-independent vasodilation as compared with the case of the control group. Administration of E2 resulted in increased basal NO release (assessed indirectly by measuring the constrictor response to N(G)-nitro-L-arginine [methyl ester (L-NAME)]) when compared with the case of the control group, and the addition of MPA to E2 did not alter the effect of E2 on basal NO release.

CONCLUSION(S)

Estradiol potentiates endothelium-dependent relaxant responses and increases basal endothelial NO release. Medroxyprogesterone acetate does not antagonize these effects of E2.

Quantitative in vivo assessment of arginine utilization and nitric oxide production in endotoxemia

BACKGROUND

Until recently no methods were available to quantitate nitric oxide (NO) production in vivo. The advent of stable isotope techniques has allowed quantitation of NO production in different animal models and human disease states.

METHODS

In vivo NO production was assessed with the use of stable isotope labeled arginine. Enrichments of metabolites were measured by liquid chromatography-mass spectrometry (LC-MS). Knock-out mice were used to assess the influence of knocking out inducible NOS (iNOS) or constitutively expressed NOS (cNOS) on arginine-NO metabolism. Pig models were used to assess the role of individual organs on arginine-NO fluxes.

RESULTS

In mice under basal conditions cNOS mediates half of the NO production. After endotoxin challenge NO production doubles as a result of iNOS induction and cNOS-mediated NO production is downregulated. In larger animal models (pig) whole body NO production is augmented after endotoxin challenge, largely resulting from NO production in liver, intestine and kidney. Arginine supplementation increases NO production in pigs in liver, intestine and kidney both in the basal state and after endotoxin challenge.

CONCLUSIONS

Stable isotope techniques employing LC-MS allow in vivo assessment of NO production in small and large animal models and in patients. This allows definition of the role that iNOS and cNOS-mediated NO production play in several disease states.

Differential effects of selective and non-selective NOS inhibition on renal arginine and protein metabolism during endotoxemia in rats

BACKGROUND AND AIMS

The kidney is the main endogenous producer of circulating arginine. Renal arginine disposal is directed to protein synthesis, urea production and nitric oxide synthesis. The administration of nitric oxide synthase inhibitors during sepsis may be beneficial or detrimental depending on the specificity of the inhibitor. We aimed to measure the effects of two NOS inhibitors, with different specificity, on renal arginine and protein turnover in a rat model of sepsis.

METHODS

Rats were subject to double hit endotoxemia and either L-NAME (non-specific), SMT (iNOS specific) or saline. Under anesthesia, vessels supplying and draining the kidney were catheterized. Systemic and intra-renal arginine and protein metabolism were measured using a primed continuous infusion of L-[2,3-(3)H]arginine and L-[2,6-(3)H]phenylalanine.

RESULTS

Non-specific NOS reduced systemic protein and arginine turnover, whereas selective iNOS inhibition did not. In the kidney, blood flow was reduced by L-NAME, but not by SMT. In conjunction with this, non-selective NOS inhibition increased renal protein breakdown, whereas selective iNOS inhibition increased renal arginine production.

CONCLUSIONS

This study shows that non-selective NOS inhibition using L-NAME is detrimental for systemic and renal protein metabolism. Selective NOS inhibition stimulates renal arginine synthesis, without changing circulating arginine levels.

Leishmania (L.) amazonensis-induced inhibition of nitric oxide synthesis in host macrophages

Inhibition of lipopolysaccharide (LPS)-induced nitric oxide (NO) production was demonstrated in J774-G8 macrophages infected with Leishmania (L.) amazonensis promastigotes. The downmodulation of NO production observed in infected and LPS-stimulated J774-G8 cells correlated with a reduction in inducible nitric oxide synthase (iNOS) activity. Reduction in iNOS activity was not paralleled by decreased iNOS mRNA expression, suggesting that the parasite affects post-transcriptional events of NO synthesis. Supplementation with L-arginine or tetrahydrobiopterin did not increase NO production, suggesting that inhibition is not due to an insufficiency of substrate or co-factor. Treatment with anti-IL-10, anti-IL-4 or anti-TGF-beta neutralizing antibodies also failed to increase NO production, indicating that these cytokines are not involved in the observed parasite-induced inhibition of NO synthesis. However, treatment of the cultures with IFN-gamma resulted in a marked increase in NO production by infected LPS-stimulated cells. These results show that although L.(L.) amazonensis infection inhibits iNOS activity and NO production by J774-G8 cells, activation by IFN-gamma is capable of overriding the suppression of NO synthesis.

Nitric oxide modulates evoked catecholamine release from canine adrenal medulla

Nitric oxide has various actions, acting in a neurotransmitter-like role and also as a paracrine messenger between vascular endothelial and smooth muscle cells. This study was done to determine whether endogenous nitric oxide has a role in modulating evoked catecholamine release from the canine adrenal medulla. Isolated adrenal glands were perfused with Krebs-Ringer solution as a control, or with Krebs-Ringer solution containing either N(G)-monomethyl-L-arginine (L-NMMA; 3x10(-4) M) to non-selectively inhibit nitric oxide synthase or 7-nitroindazole (10(-4) M), a relatively selective inhibitor of neuronal nitric oxide synthase. Catecholamine release was evoked using the nicotinic cholinergic agonist 1,1-dimethyl-4-phenylpiperazinium iodine. From the collected perfusate epinephrine, norepinephrine, and dopamine were measured by high performance liquid chromatography. Previous studies have shown that in the presence of L-NMMA, basal releases of epinephrine, norepinephrine and dopamine are increased. 7-Nitroindazole had no effect on basal catecholamine release, suggesting that nitric oxide from an endothelial source was responsible for the inhibition of basal catecholamine release from the adrenal medulla. Epinephrine and norepinephrine releases were augmented when either of the nitric oxide synthase inhibitors was added during submaximal nicotinic stimulation, indicating that endogenous nitric oxide inhibited release of epinephrine and norepinephrine. Both neuronal and endothelial nitric oxide synthases appeared to be responsible for this inhibition. In summary, these studies suggest that nitric oxide, from both neuronal and endothelial sources, modulates evoked catecholamine release from canine adrenal medulla, while nitric oxide from an endothelial source is most likely responsible for modulation of catecholamine release under basal conditions.

Nitric oxide in gastrointestinal epithelial cell carcinogenesis: linking inflammation to oncogenesis

Chronic inflammation of gastrointestinal tissues is a well-recognized risk factor for the development of epithelial cell-derived malignancies. Although the inflammatory mediators linking chronic inflammation to carcinogenesis are numerous, current information suggests that nitric oxide (NO) contributes to carcinogenesis during chronic inflammation. Inducible nitric oxide synthase (iNOS), expressed by both macrophages and epithelial cells during inflammation, generates the bioreactive molecule NO. In addition to causing DNA lesions, NO can directly interact with proteins by nitrosylation and nitosation reactions. The consequences of protein damage by NO appear to be procarcinogenic. For example, NO inhibits DNA repair enzymes such as human 8-oxodeoxyguanosine DNA glycosylase 1 and blocks apoptosis via nitrosylation of caspases. These cellular events permit DNA damage to accumulate, which is required for the numerous mutations necessary for development of invasive cancer. NO also promotes cancer progression by functioning as an angiogenesis factor. Strategies to inhibit NO generation during chronic inflammation or to scavenge reactive nitrogen species may prove useful in decreasing the risk of cancer development in chronic inflammatory gastrointestinal diseases.

Arginine metabolism and the synthesis of nitric oxide in the nervous system

The biochemistry and physiology of L-arginine have to be reconsidered in the light of the recent discovery that the amino acid is the only substrate of all isoforms of nitric oxide synthase (NOS). Generation of nitric oxide, NO, a versatile molecule in signaling processes and unspecific immune defense, is intertwined with synthesis, catabolism and transport of arginine which thus ultimately participates in the regulation of a fine-tuned balance between normal and pathophysiological consequences of NO production. The complex composition of the brain at the cellular level is reflected in a complex differential distribution of the enzymes of arginine metabolism. Argininosuccinate synthetase (ASS) and argininosuccinate lyase which together can recycle the NOS coproduct L-citrulline to L-arginine are expressed constitutively in neurons, but hardly colocalize with each other or with NOS in the same neuron. Therefore, trafficking of citrulline and arginine between neurons necessitates transport capacities in these cells which are fulfilled by well-described carriers for cationic and neutral amino acids. The mechanism of intercellular exchange of argininosuccinate, a prerequisite also for its proposed function as a neuromodulator, remains to be elucidated. In cultured astrocytes transcription and protein expression of arginine transport system y(+) and of ASS are upregulated concomittantly with immunostimulant-mediated induction of NOS-2. In vivo ASS-immunoreactivity was found in microglial cells in a rat model of brain inflammation and in neurons and glial cells in the brains of Alzheimer patients. Any attempt to estimate the contributions of arginine transport and synthesis to substrate supply for NOS has to consider competition for arginine between NOS and arginase, the latter enzyme being expressed as mitochondrial isoform II in nervous tissue. Generation of NOS inhibitors agmatine and methylarginines is documented for the nervous system. Suboptimal supply of NOS with arginine leads to production of detrimental peroxynitrite which may result in neuronal cell death. Data have been gathered recently which point to a particular role of astrocytes in neural arginine metabolism. Arginine appears to be accumulated in astroglial cells and can be released after stimulation with a variety of signals. It is proposed that an intercellular citrulline-NO cycle is operating in brain with astrocytes storing arginine for the benefit of neighbouring cells in need of the amino acid for a proper synthesis of NO.

Suppression by a sesquiterpene lactone from Carpesium divaricatum of inducible nitric oxide synthase by inhibiting nuclear factor-kappaB activation

Excessive nitric oxide (NO) produced by inducible NO synthase (iNOS) acts as a causative regulator in various inflammatory disease states. Carpesium divaricatum has been used in Korean traditional herbal medicine for its antipyretic, analgesic, vermifugic, and anti-inflammatory properties. We investigated the molecular mechanism for the suppression of lipopolysaccharide/interferon-gamma (LPS/IFN-gamma)-induced NO production in RAW 264.7 macrophages by the sesquiterpene lactone 2beta,5-epoxy-5,10-dihydroxy-6alpha-angeloyloxy-9beta-isobutyloxy-germacran-8alpha,12-olide (C-1), which has been identified recently as a new compound from C. divaricatum. C-1 decreased NO production in LPS/IFN-gamma-stimulated RAW 264.7 cells in a concentration-dependent manner, with an IC50 of approximately 2.16 microM; however, it had no direct effect on the iNOS activity of fully LPS/IFN-gamma-stimulated RAW 264.7 cells. Furthermore, treatment with C-1 led to a decrease in iNOS protein and mRNA. These effects appear to be due to inhibition of nuclear factor-kappaB (NF-kappaB) activation through a mechanism involving stabilization of the NF-kappaB/inhibitor of the kappaB (I-kappaB) complex, since inhibition of NF-kappaB DNA binding activity by C-1 was accompanied by a parallel reduction of nuclear translocation of subunit p65 of NF-kappaB and I-kappaBalpha degradation. Taken together, the results suggest that the ability of C-1 to inhibit iNOS gene expression may be responsible, in part, for its anti-inflammatory effects.

Relative importance of nitric oxide and carbon monoxide in regulating the ACTH response to immune and non-immune signals

The present work investigated the effect of nitric oxide (NO) or carbon monoxide (CO) in the ACTH response to an immune signal [the intravenous injection of interleukin-1 β (IL-1β)] or to a neurogenic stressor (mild intermittent inescapable foot shocks). The arginine derivative N(ω)-L-arginine methylester (L-NAME), which non-specifically inhibits NO formation induced by all constitutive forms of NO synthase (NOS), significantly augmented the effect of IL-1P,but blockade of CO formation with metalloporphyrins was without effect. On the other hand, L-NAME blunted the effect of shocks on the early phase of ACTH release, while we had reported earlier that metalloporphyrins exerted a similar effect. This effect was mimicked by blockade of neuronal (n) NOS by N(ω)-Propyl-L-arginine (PA), although the resulting decrease in hormone levels was less than that induced by L-NAME. These results indicate that endogenous NO, but not CO, interferes with ACTH released by a peripheral immune signal. In contrast, NO formed by nNOS enhances the ability of shocks to induce ACTH secretion.

Inhibition by ginkgolides and bilobalide of the production of nitric oxide in macrophages (THP-1) but not in endothelial cells (HUVEC)

Nitric oxide (NO) is a principal mediator in many physiological and pathological processes. NO produced by constitutive nitric oxide synthase in endothelial cells (eNOS) acts as a vasodilator, whereas excess NO production due to elevated expression of inducible nitric oxide synthase (iNOS) may produce cytotoxic effects to cells in the vascular wall. We demonstrated in our previous work that the extract of Ginkgo biloba leaves (EGb) inhibits iNOS-mediated NO production. The objective of the present study was to investigate the effects of several active EGb components on iNOS-mediated NO production in macrophages derived from a human monocytic cell line (THP-1), as well as on eNOS-mediated NO production in human umbilical vein endothelial cells (HUVEC). Ginkgolide A, ginkgolide B, or bilobalide (0.25 to 1.0 microg/mL) caused a 30-65% reduction in the levels of NO metabolites released by THP-1 macrophages after 4 hr of incubation, with a corresponding decrease in iNOS activity. Western immunoblotting analysis coupled with a nuclease protection assay and reverse transcription-polymerase chain reaction revealed a concomitant reduction in the levels of iNOS protein mass and mRNA in ginkgolide A-, ginkgolide B-, or bilobalide-treated macrophages. On the other hand, these compounds did not affect eNOS-mediated NO production or the expression of eNOS protein and mRNA in HUVEC. Taken together, these results suggest that ginkgolide A, ginkgolide B, and bilobalide may contribute to the selective inhibitory effect of EGb on iNOS expression without affecting eNOS-mediated NO production.

Endogenous nitric oxide and prostaglandins synergistically counteract thromboembolism in arterioles but not in venules

It has been shown that NO and prostacyclin (prostaglandin I(2)) from cultured endothelium synergistically inhibit blood platelet aggregation in vitro. However, it is unknown whether this synergism is also effective in the inhibition of thromboembolism in vivo and, if it is, whether it differs between vessel types. Therefore, the effect of endogenous NO and prostacyclin, in combination or alone, on thromboembolism was studied in an in vivo model. Thromboembolism was induced by micropipette puncture of rabbit mesenteric arterioles and venules (diameter 18 to 40 micrometer). In addition, the influence of wall shear rate was analyzed. In arterioles, the combined inhibition of NO synthase (N(G)-nitro-L-arginine [L-NA] 0.1 mmol/L; local superfusion) and of cyclooxygenase (aspirin [ASA] 100 mg/kg IV) resulted in a pronounced, significant prolongation of embolization duration (median >600 seconds) compared with control (median 153 seconds) or treatment with either L-NA (234 seconds) or ASA (314 seconds). This combined effect of L-NA+ASA was greater than the sum of the individual effects of L-NA and ASA. In contrast, in venules L-NA+ASA had no additional effect on embolization duration (209 seconds) compared with the effect of L-NA alone (230 seconds); ASA alone had no effect (122 seconds; control 72 seconds). Interestingly, only in the L-NA+ASA arterioles did embolization correlate positively with wall shear rate (r(s)=0.687; P=0.028). In conclusion, this study indicates that in arterioles, but not in venules, endogenous NO and prostaglandins synergistically counteract ongoing thromboembolism after vessel wall injury and that the combination of endogenous NO and prostaglandins appears to protect against enhancement of arteriolar thromboembolism by wall shear rate.

Suppression of inducible nitric oxide synthase expression in RAW 264. 7 macrophages by two beta-carboline alkaloids extracted from Melia azedarach

We investigated the mechanism of suppression of inducible nitric oxide synthase (iNOS) by two beta-carboline alkaloids isolated from Melia azedarach, 4,8-dimethoxy-1-vinyl-beta-carboline (compound 1, C-1) and 4-methoxy-1-vinyl-beta-carboline (compound 2, C-2). iNOS activity in a cell-free extract of lipopolysaccharide/interferon-gamma-stimulated RAW 264.7 cells was found to be markedly increased, and this increase was prevented by C-1 and C-2, accompanied by the parallel reduction in nitrite accumulation in culture medium. However, C-1 and C-2 had no further effect on the iNOS activity prepared from fully lipopolysaccharide/interferon-gamma-stimulated RAW 264.7 cells. Treatment with C-1 or C-2 decreased the levels of iNOS protein and mRNA in a concentration-dependent manner. In addition, prostaglandin E(2) production, cyclooxygenase-2 protein and DNA binding of nuclear factor-kappaB (NF-kappaB) in lipopolysaccharide-stimulated RAW 264.7 cells were reduced by these compounds. These results indicate that C-1 and C-2 primarily inhibit iNOS and cyclooxygenase-2 activities via the suppression of de novo synthesis of these two enzymes, and that the inhibition of iNOS expression may be associated with the inhibition of NF-kappaB activation. Taken together, the results suggest that suppression of iNOS and cyclooxygenase-2 induction by lipopolysaccharide is responsible for the anti-inflammatory activity of these alkaloids through selective inhibition of the expression of genes, which play important roles in inflammatory signaling pathways.

Galactosamine decreases nitric oxide formation in cultured rat hepatocytes: mechanism of suppression

We have shown that nitric oxide production is dramatically decreased in rat primary hepatocyte cultures exposed to galactosamine. Cotreatment of the cells with uridine, which is known to prevent cytotoxicity, was found to also attenuate NO loss. In the present study, two possible mechanisms for the decreased nitric oxide production were examined. First, we examined the possibility that galactosamine could interfere with the uptake of extracellular arginine by the cultured hepatocytes. Cellular uptake of arginine was determined after addition of 14C-arginine at the time of hepatocyte attachment. Uptake of arginine was rapid in control cultures, and both the rate and level of uptake were unchanged by the addition of a cytotoxic concentration of galactosamine (4 mM). In addition, increased concentrations of arginine in the cell culture medium did not ameliorate the galactosamine-induced decrease in production of nitric oxide. Second, we determined whether the synthesis of inducible nitric oxide synthase in the hepatocyte cultures was inhibited by addition of galactosamine. Hepatocyte levels of inducible nitric oxide synthase were determined immunochemically at various times after the addition of galactosamine (4 mM). In control cultures, inducible nitric oxide synthase was detectable at 7 and 24 hours after attachment. In contrast, no nitric oxide synthase protein was detectable at any time in the galactosamine-treated cultures. Furthermore, addition of galactosamine after inducible nitric oxide synthase had already been synthesized (6.5 h after attachment) did not result in suppression of nitric oxide production in the hepatocyte cultures. The present studies suggest that galactosamine suppresses nitric oxide production in hepatocyte cultures by inhibiting synthesis of inducible nitric oxide synthase, rather than by interference in cellular uptake of arginine.

Role of nitric oxide in diabetes-induced attenuation of antinociceptive effect of morphine in mice

The study was designed to investigate the role of nitric oxide (NO) in the diabetes-induced decrease of the antinociceptive effect of morphine. The nociceptive threshold in diabetic and non-diabetic mice was measured in the tail-flick test. Streptozotocin (200 mg/kg i.p.) was administered to induce experimental diabetes in the mice. Four weeks after the administration of streptozotocin, the tail-flick test was performed and urinary nitrite concentration was estimated using Greiss reagent. Experimental diabetes markedly decreased the antinociceptive effect of morphine (10 microg in 5 microl/mice i.c.v.) and significantly increased the urinary nitrite concentration. Administration of aminoguanidine (12 mg/mice) markedly improved the antinociceptive effect of morphine and attenuated the increase in urinary nitrite concentration in diabetic mice. It may be tentatively concluded that an increase in NO formation may be responsible for the observed decrease in antinociceptive effect of morphine in diabetic mice.

Protective effects of cyclosporin-A in splanchnic artery occlusion shock

Cyclosporin A (CsA) is an immunosuppressant drug that inhibits nitric oxide (NO) synthase induction in vascular smooth muscle cells. Splanchnic artery occlusion (SAO) shock is a lethal type of shock characterized by a marked vascular dysfunction in which the L-arginine/nitric oxide pathway plays an important role. We investigated whether CsA exerts protective effects in SAO shock by interfering with the L-arginine/nitric oxide pathway. Male anaesthetized rats (n=156) were subjected to clamping of the splanchnic arteries for 45 min. This surgical procedure resulted in an irreversible state of shock (SAO shock). Sham operated animals were used as controls. SAO shocked rats had a decreased survival (86+/-6 min, while sham shocked rats survived more than 240 min), marked hypotension, increased serum levels of TNF-alpha, enhanced plasma nitrite/nitrate concentrations (75+/-7.1 microM; sham shocked rats=1.6+/-0.5 microM) and enhanced inducible NO synthase (iNOS) protein induction and activity in the aorta. Moreover aortic rings from shocked rats showed a marked hyporeactivity to phenylephrine (PE, 1 nM - 10 microM). CsA (0.25, 0.5 and 1 mg kg(-1), 5 min after reperfusion) increased survival rate (SAO+CsA=236+/-9 min following the highest dose), reverted the marked hypotension, reduced plasma nitrite/nitrate concentration (11+/-5.2 microM following the highest dose), restored to control values the hyporeactivity to PE, and blunted iNOS protein induction and activity in aortic rings. The present data indicate that in an experimental rat model CsA may have antishock properties related to inhibition of L-arginine/nitric oxide pathway.

Effect of magnesium tanshinoate B on the production of nitric oxide in endothelial cells

Nitric oxide (NO) is a potent vasodilator which plays an important role in regulating vascular tones. Danshen, a Chinese herbal medicine has been widely used for the treatment of cardiovascular diseases. The objective of this study was to investigate the effect of magnesium tanshinoate B (MTB), a compound purified from Danshen, on the production of NO in human endothelial cell line (ECV304). After cells were incubated with MTB (1-10 microM) for 1 or 4 h, amounts of NO metabolites released by cells were quantified and cellular NOS activities were determined following the conversion of [3H]arginine to [3H]citrulline. The NOS protein expression was determined by Western immunoblotting analysis. MTB (1-10 microM) stimulated the release of NO and its metabolites from endothelial cells. Following MTB treatment, the cellular NOS activities were significantly enhanced with a concomitant increase in the levels of constitutive NOS (cNOS) protein mass (110-178%). Selective activation of cNOS by MTB may be employed therapeutically in modulating NO production in endothelial cells.

Measurement of 3-nitrotyrosine and 5-nitro-gamma-tocopherol by high-performance liquid chromatography with electrochemical detection

Nitric oxide (NO) is a lipophilic gaseous molecule synthesized by the enzymatic oxidation of L-arginine. During periods of inflammation, phagocytic cells generate copious quantities of NO and other reactive oxygen species. The combination of NO with other reactive oxygen species promotes nitration of ambient biomolecules, including protein tyrosine residues and membrane-localized gamma-tocopherol. The oxidative chemistry of NO and derived redox congeners is reviewed. Techniques are described for the determination of 3-nitro-tyrosine and 5-nitro-gamma-tocopherol in biological samples using high-performance liquid chromatography with electrochemical detection.

Effects of some isoxazolpyrimidine derivatives on nitric oxide and eicosanoid biosynthesis

The inhibitory effect of some isoxazolpyrimidine derivatives on iNOS and COX-2 endotoxin induction in mouse peritoneal macrophages has been studied. Three of these compounds inhibited nitrite and PGE2 accumulation in a concentration dependent-manner at microM range. None of these active compounds affected iNOS, COX-2, COX-1 or PLA2 activities, although some reduced iNOS or COX-2 expression. Besides, no effect was observed on human neutrophil inflammatory responses (LTB4 biosynthesis and superoxide or elastase release). Active compounds were assayed by oral administration in the mouse air pouch model, where they inhibited nitrite accumulation without affecting PGE2 levels or leukocyte migration.

Inhibitory effect of Ginkgo biloba extract on the expression of inducible nitric oxide synthase in endothelial cells

Excessive production of nitric oxide (NO) may have cytotoxic effects through the formation of peroxynitrite with superoxide. The extract of Ginkgo biloba leaves (EGb) has been demonstrated to be a potent scavenger of free radicals. Although EGb has been shown recently to inhibit NO production in macrophages, its effect on NO production in endothelial cells is largely unknown. The objective of this study was to elucidate the mechanism by which EGb affects NO production in a human endothelial cell line (ECV304). After cells were incubated with EGb (10-100 microg/mL) for 2 or 4 hr, the amounts of NO metabolites released by the cells were quantitated, and cellular NOS activities were determined following the conversion of [3H]arginine to [3H]citrulline. NOS protein expression was determined by western immunoblotting analysis. mRNA levels were examined by reverse transcription-polymerase chain reaction (RT-PCR) analysis. EGb (50 microg/mL) caused a 30% reduction of NO metabolites released by endothelial cells. Following EGb treatment, cellular inducible NO synthase (iNOS) activity was reduced by 28% with a concomitant reduction in the levels of iNOS protein mass and mRNA. There was no change in the activity or protein mass of constitutive NO synthase in these cells. EGb inhibited NO production by attenuating the level of iNOS mRNA in ECV304 cells. Selective inhibition of iNOS by EGb may be therapeutically relevant in modulating NO production in endothelial cells.

Synthesis and pharmacological evaluation of some 8-cyanopyrido[3', 2':4,5]thieno[3,2-d]triazine derivatives as inhibitors of nitric oxide and eicosanoid biosynthesis

A series of 8-cyanopyrido[3',2':4,5]thieno[3,2-d]-1,2,3-triazines, substituted at C-4 and C-7, were synthesized and evaluated as nitric oxide and prostaglandin E(2) inhibitors in murine peritoneal macrophages stimulated with bacterial endotoxin. Several compounds exhibited considerable activity, compounds 10 and 13 being the most interesting ones with IC(50) values of 11.2 and 3.4 microM on nitrites and 0.9 and 0.6 microM on prostaglandin E(2) production, respectively. None of the examples of pyridothienotriazines that were active at 10 microM showed any effect on inducible nitric oxide synthase, cyclooxygenase-2, and cyclooxygenase-1 enzymes, suggesting that they act by modifiying the level of expression of these inducible enzymes.

Nitric Oxide and the Th2 Response Combine to Prevent Severe Hepatic Damage During Schistosoma mansoni Infection

During infection with Schistosoma mansoni, NO production increases following the deposition of parasite eggs in the liver. In wild-type C57BL/6 mice, NO levels peak during the sixth week of infection and are subsequently down-regulated. Inducible NO synthase (iNOS) mRNA was found in diseased liver tissue along with TNF-α and IFN-γ, which are known promoters of iNOS expression. Mice treated with aminoguanidine, a selective inhibitor of iNOS, exhibited cachexia and exacerbated liver pathology, suggesting that NO limits hepatocyte damage when the liver is first exposed to eggs. Hepatic iNOS is up-regulated in SCID mice, indicating that NO production is part of an innate response. Studies with infected highly susceptible IL-4−/− mice revealed that prolonged NO production is in itself deleterious and that a major function of the Th2 response, which is severely compromised in the absence of IL-4, is to regulate NO production. In these animals, plasma NO levels are high compared with those in infected wild-type mice and remain elevated until death. Nevertheless, the underlying importance of NO is illustrated by the finding that aminoguanidine treatment leads to more severe liver disease and reduced time to death in infected IL-4−/− mice.

Leptin increases serotonin turnover by inhibition of brain nitric oxide synthesis

Leptin administration inhibits diencephalic nitric oxide synthase (NOS) activity and increases brain serotonin (5-HT) metabolism in mice. We evaluated food intake, body-weight gain, diencephalic NOS activity, and diencephalic content of tryptophan (TRP), 5-HT, hydroxyindoleacetic acid (5-HIAA), and 5-HIAA/5-HT ratio after intracerebroventricular (ICV) or intraperitoneal (IP) leptin injection in mice. Five consecutive days of ICV or IP leptin injections induced a significant reduction in neuronal NOS (nNOS) activity, and caused a dose-dependent increase of 5-HT, 5-HIAA, and the 5-HIAA/5-HT ratio. Diencephalic 5-HT metabolism showed a significant increase in 5-HT, 5-HIAA, and the 5-HIAA/5-HT ratio 3 hours after a single leptin injection. This effect was maintained for 3 hours and had disappeared by 12 hours after injection. After a single IP leptin injection, the peak for 5-HT, 5-HIAA, and the 5-HIAA/5-HT ratio was achieved at 6 hours. Single injections of ICV or IP leptin significantly increased diencephalic 5-HT content. Leptin-induced 5-HT increase was antagonized by the coadministration of L-arginine only when the latter was ICV injected, whereas D-arginine did not influence leptin effects on brain 5-HT content. Finally, in nNOS-knockout mice, the appetite-suppressant activity of leptin was strongly reduced, and the leptin-induced increase in brain 5-HT metabolism was completely abolished. Our results indicate that the L-arginine/NO pathway is involved in mediating leptin effects on feeding behavior, and demonstrate that nNOS activity is required for the effects of leptin on brain 5-HT turnover.

L-arginine binding to nitric-oxide synthase. The role of H-bonds to the nonreactive guanidinium nitrogens

Nitric-oxide synthase (NOS) catalyzes the oxidation of L-arginine to nitric oxide and L-citrulline. Because overproduction of nitric oxide causes tissue damage in neurological, inflammatory, and autoimmune disorders, design of NOS inhibitors has received much attention. Most inhibitors described to date include a guanidine-like structural motif and interact with the guanidinium region of the L-arginine-binding site. We report here studies with L-arginine analogs having one or both terminal guanidinium nitrogens replaced by functionalities that preserve some, but not all, of the molecular interactions possible for the -NH(2), =NH, or =NH(2)(+) groups of L-arginine. Replacement groups include -NH-alkyl, -alkyl, =O, and =S. Binding of L-canavanine, an analog unable to form hydrogen bonds involving a N(5)-proton, was also examined. From our results and previous work, we infer the orientation of these compounds in the L-arginine-binding site and use IC(50) or K(i) values and optical difference spectra to quantitate their affinity relative to L-arginine. We find that the non-reactive guanidinium nitrogen of L-arginine binds in a pocket that is relatively intolerant of changes in the size or hydrogen bonding properties of the group bound. The individual H-bonds involved are, however, weaker than expected (<2 versus 3-6 kcal). These findings elucidate substrate binding forces in the NOS active site and identify an important constraint on NOS inhibitor design.

High-dose heparin impairs nitric oxide pathway and vasomotion in rats

BACKGROUND

Platelet-activating effects have been reported with high-dose heparin in acute thrombotic disorders. Recent studies have shown that increased platelet aggregation is due to reduced nitric oxide (NO) production in endothelial cells cultured in the presence of high-dose heparin. The aim of this study was to determine whether heparin can affect the NO pathway and the regulation of the vascular tone in vivo.

METHODS AND RESULTS

Anesthetized and mechanically ventilated Sprague-Dawley rats were treated with high-dose heparin. After 4 hours, the endothelial constitutive NO synthase (ecNOS) protein content in the aorta decreased (36% reduction, P<0.05), as detected by immunoblotting, and NO-dependent vascular reactivity was impaired. In fact, the increase in mean arterial blood pressure after inhibition of ecNOS with NG-nitro-L-arginine methyl ester (30 mg/kg) was smaller in heparin-treated animals than in controls (+26. 9+/-4.8 versus +48.3+/-9.1 mm Hg, P<0.05), and further infusion of the biological ecNOS substrate L-arginine (0.5 g/kg) was ineffective in reversing systemic vasoconstriction (-1% versus 28% vasodilatation, P<0.001).

CONCLUSIONS

High-dose heparin can significantly affect vascular reactivity in vivo by downregulation of ecNOS protein expression.

Evidence that nitric oxide stimulates feeding in the marsupial Sminthopsis crassicaudata

Nitric oxide (NO) synthase inhibitors reduce food intake in rodents and chickens, suggesting that NO may stimulate feeding. We used two competitive, non-selective inhibitors of NO synthase (NOS), (NG-monomethyl-L-arginine ester [L-NMMA] and NG-nitro-L-arginine methyl ester [L-NAME]), to evaluate the role of NO mechanisms in the control of food intake in a marsupial model previously used in studies of appetite regulation. Adult male Sminthopsis crassicaudata (n = 11-16, 15 +/- 0.3 g, mean +/- S.E.M.) received L-NMMA (50, 100, 200 and 1000 mg/kg), L-NAME (50, 100 and 200 mg/kg), L-arginine (L-arg) the precursor of NO (1000 and 2000 mg/kg), L-NAME (200 mg/kg) in combination with L-arg (2000 mg/kg), or saline (0.9%). All drugs were administered intraperitoneally after 24 h of food deprivation, after which food was immediately made available ad libitum. Food intake was measured 0, 0.5, 1, 2, 4 and 24 h after treatments. In addition, we studied the effect of acute L-NAME administration on hypothalamic, cortical, hepatic and cardiac NOS activity by quantifying citrulline production. L-NMMA (1000 mg/kg) and L-NAME (100 and 200 mg/kg) suppressed food intake by 25%, 21%, and 30%, respectively, over 24 h after treatments (P < 0.05). L-arg (1000 and 2000 mg/kg) by itself had no significant effect on food intake when compared with saline (P > 0.05). When administered in combination with L-NAME (200 mg/kg), L-arg (2000 mg/kg) reversed L-NAME induced suppression of appetite (P> 0.05). Furthermore, L-NAME (200 mg/kg) significantly decreased hypothalamic (P < 0.01), cortical (P < 0.01) and hepatic (P < 0.03) NOS activity. L-NAME had no effect on cardiac NOS activity (P> 0.05). These data show that peripheral administration of L-NAME has a significant central effect, particularly in brain areas involved in appetite regulation, and suggest in marsupials, as in other mammals and birds, that NO plays a role in the regulation of food intake.