The L-arginine-nitric oxide pathway

Influence of basal nitric oxide secretion on cardiac function in man

1. Nitric oxide is recognised as an important biological mediator, which is thought to be involved in cardiovascular homeostasis. The purpose of this study was to investigate the effects of basal nitric oxide synthesis on cardiac function in man, by blocking nitric oxide synthesis with NG-monomethyl-L-arginine (L-NMMA). 2. Eight normal volunteers were studied on two separate occasions. Measurements of heart rate, blood pressure and echocardiographic indices of left ventricular systolic and diastolic function were made at baseline on each day and every 20 min during incremental infusion of L-NMMA (0.1, 0.2, 0.5, 1.0 and 2.0 mg kg-1 h-1) or placebo. 3. A trend towards reduction in heart rate was observed with L-NMMA infusion although this did not reach statistical significance, whereas significant increases in both systolic blood pressure (at 2.0 mg kg-1 h-1) and systemic vascular resistance index (at 0.5 mg kg-1 h-1) were seen. 4. L-NMMA infusion caused significant reductions in stroke distance and cardiac index, although there was no change in the ratio of end systolic wall stress/end systolic volume index (an afterload independent index of left ventricular systolic performance). 5. The isovolumic relaxation time significantly increased with L-NMMA infusion, together with a significant reduction in the 'E' wave flow velocity integral. Reductions in both peak E/A ratio and E/A flow velocity integral ratio were also seen, although these failed to reach statistical significance. 6. In conclusion, the basal generation of nitric oxide in man appears to maintain a vasodilated state, and modifies left ventricular diastolic filling parameters.

Early embryo loss is associated with local production of nitric oxide by decidual mononuclear cells

In early embryo loss, the fetus may be considered to be an allograft and, therefore, may be rejected by maternal immunocytes. However, the cytotoxic mechanisms involved are still poorly understood. We have previously shown the involvement of natural killer (NK) cells and mononuclear cells expressing Mac-1 (CD11b) and F4/80 in resorbing compared to nonresorbing embryos. In this study, the role of nitric oxide (NO) in the mechanism of early embryo loss was studied. Pregnant CBA/J females mated with DBA/2 males (20-30% early embryo loss) and CD1 females mated with CD1 males (5-10% early embryo loss) were studied on days 8, 10, and 12 of gestation. Cells from the implantation sites of individual embryos were tested for the production of nitrite and nitrate with or without in vitro challenge with lipopolysaccharide (LPS) to determine whether decidual macrophages were primed in situ. On day 12 of gestation, when resorption was clearly visible, resorbing embryos showed more than a fivefold increase in both basal- and LPS-induced nitrite and nitrate production compared to nonresorbing embryos in both mouse strains tested, indicating that the decidual mononuclear cells were primed. Furthermore, more than 20% of CBA/J embryos showed a significant nitrate release on days 8 and 10 of gestation before any signs of embryo cytopathology. This percentage corresponded to the spontaneous resorption rate seen in CBA/J female X DBA/2 male matings. Similarly, 4% of the embryos from pregnant CD1 mice on days 8 and 12 of gestation produced a significant amount of nitrate, which again correlated with the low incidence of resorption observed in these mice. Using immunohistochemistry, the presence of inducible nitric oxide synthase (iNOS) was detected at implantation sites. Furthermore, decidual cells positive for both iNOS and the macrophage marker Mac-1 were demonstrated in implantation sites by double immunostaining. This strongly suggests that decidual macrophages could be the cellular source of NO production. Aminoguanidine, a selective inhibitor of the iNOS, inhibited the in vitro production of nitric oxide by cells isolated from individual implantation sites, and more strikingly, significantly reduced early embryo losses in CBA/J females mated by DBA/2 males when given orally or parenterally to the gravid females starting on day 6 of gestation. In addition, aminoguanidine-treated pregnant mice showed a significant increase in average litter size when the pregnancies were allowed to proceed to term.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of two administration techniques of inhaled nitric oxide on nitrogen dioxide production

The purpose of this study was to verify whether, compared with the introduction of the NO-N2 mixture at the air inlet of the ventilator (classical method), a direct injection of NO-N2 into the inspiratory line of the ventilator circuit with a new injection device (new method), would reduce NO2 formation by reducing contact time between O2 and NO. The effect of two FIO2(0.21 and 0.90) and NO concentrations on NO2 production was determined. In the classical method, NO and O2 were mixed with an air/oxygen blender before the gas mixture entered the ventilator. In the new method, NO was injected directly into the respiratory line with the injection system. Nitric oxide and nitrogen dioxide gases were measured using a chemiluminescence analyzer. For a FI02 of 0.90 and 90 ppm of NO2, the amount of NO2 produced was decreased from 8.9 +/- 0.8 ppm (mean +/- SD) with the classical injection system to 4.4 +/- 0.2 ppm with the new injection system (P = 0.0039, Mann-Whitney test), and NO2 production was decreased from 4.5 +/-0.2 ppm to 2.1 +/- 0.4 ppm (P = 0.02) at 60 ppm of NO. However, at a FIO2, no difference was found in the amount of NO2 produced. We conclude that, compared with the classical method of NO administration, the new NO injection system reduces considerably the concentration of inhaled NO2 when a high FIO2 and a high concentration of NO are used.

Local anesthetic effects in the presence of chronic osteomyelitis (necrosis) of the mandible: implications for localizing the etiologic sites of referred trigeminal pain

The aims of this study were: (1) to demonstrate how reproducible variations in incomplete anesthesia of the inferior alveolar nerve can be used as a guide to locate the etiologic sites of referred trigeminal pain emanating from the mandible; (2) to describe the salient histopathologic features of a lowgrade, nonsuppurative osteomyelitis seen in this patient population. Forty-six patients with idiopathic facial pain were subjected to a specific protocol of local anesthetic injections to sequentially block branches of the mandibular nerve to determine the effects on his/her pain. If this significantly reduced or altered the pain on three separate appointments, then exploratory surgery was conducted near identified zones of unanesthetized gingiva. Blocking (92%), bridging (4%), and divergence (4%) were observed patterns of anesthetic resistance of the mucogingival tissues used to categorize the incomplete anesthesia. A 100% correlation was found between the identified zones of unanesthetized gingiva and the discovery of intramedullary pathology. Medullary fibrosis with ischemic and degenerative changes in the cancellous bone were common findings, along with chronic inflammatory cell infiltrates and clusters of lymphocytes. It is concluded that Ratner's method of diagnostic anesthesia be implemented when searching for occult pain producing pathology of the jaws.

Human endothelial cells bioactivate organic nitrates to nitric oxide: implications for the reinforcement of endothelial defence mechanisms

Although in therapeutic use for more than a century, the mode of cellular action of organic nitrates remains incompletely understood. Despite ample experimental evidence from animal studies to show that nitrates are metabolized to NO in the vascular smooth muscle, direct demonstration of such an activity in human vascular cells is still lacking. Moreover, the role of the endothelium in modulating the pharmacodynamic action of nitrates is far from clear. We therefore aimed to investigate whether or not human endothelial cells are capable of bioactivating these drugs to NO and whether the amounts generated are sufficient to elicit any biological effects. Using cultured human umbilical vein endothelial cells (HUVECs) as an established model system a combination of three different methods was used to address this issue: (1) quantification of NO formation upon endothelial nitrate metabolism using the oxyhaemoglobin technique; (2) evaluation of the second messenger response using radioimmunoassay for cGMP; and (3) assessment of mechanism and extent of potentiation of the anti-aggregatory effect of nitrates in the presence of endothelial cells as a relevant bioassay. We now show that superfusion of cultured human endothelial cells on microcarrier beads with either glyceryl trinitrate (GTN) or isosorbide dinitrate (ISDN; both at 0.1-100 mumol L-1) results in a concentration-dependent formation of NO. NO generation from isosorbide 5-mononitrate (IS-5-N) was below the detection limit. The amounts of NO produced (maximally 2.97 +/- 0.98 pmoles NO min-1 x mg protein with 100 mumol L-1 GTN; n = 8) were similar to those elicited upon challenge of the cells with 100 nM bradykinin. NO formation from either organic nitrate was accompanied, in a concentration-dependent and methylene blue-inhibitable manner, by stimulation of endothelial soluble guanylyl cyclase with consequent increases in the intracellular level of cGMP (maximally 32-fold over basal levels with ISDN), a significant portion of which was released into the extracellular space. Upon continuous 30 min superfusion or repeated application of high concentrations of GTN (100 mumol L-1) nitrate bioactivation to NO was subject to partial tachyphylaxis. Co-incubation of washed human platelets with HUVECs potentiated the anti-aggregatory action of nitrates in a cell number dependent and oxyhaemoglobin-sensitive manner and this effect, too, was accompanied by increases in intraplatelet cGMP levels. The potentiating effect was largely inhibited after blockade of sulfhydryl groups by pre-incubation of HUVECs with N-ethylmaleimide and completely abrogated after pretreatment of cells with the tissue fixative glutaraldehyde. These results demonstrate that human endothelial cells are capable of bioactivating organic nitrates to NO by an enzymatic, apparently thiol-sensitive pathway, in quantities sufficient to influence endothelial and platelet function. Besides the well known vasorelaxant action of organic nitrates, which is mainly due to their metabolism in the smooth muscle compartment, these drugs may therefore be endowed with a hitherto underestimated potential to directly influence endothelial functions via the NO/cGMP pathway. Through specific bioactivation in the endothelium itself organic nitrates can thus mimic and reinforce protective functions normally served by a functional endothelium such as the modulation of blood cell/vessel wall interactions and inhibition of cell proliferation.

Endothelium-derived vasoactive substances in Bartter's syndrome

An imbalance between endothelium-derived vasoactive substances such as endothelin and endothelium-derived nitric oxide (NO) might be viewed as a possible determinant of vascular hyporeactivity. To check this possibility the authors evaluated the role of endothelin and NO in the reduced vascular reactivity of Bartter's syndrome. Plasma immunoreactive endothelin (22.07 +/- 7.06 vs 13.80 +/- 1.43 pmol/L, P < 0.011), urinary excretion of NO2- (0.28 +/- 0.10 vs 0.15 +/- 0.02, mumol/mumol of urinary creatinine, P < 0.01) and NO3- (0.17 +/- 0.07 vs 0.09 +/- 0.02 mumol/mumol of urinary creatinine, P < 0.011), and forearm resting blood flow (FRBF) (6.67 +/- 1.69 vs 4.30 +/- 0.38 mL/m'/100 mL, P < 0.005) were increased in patients with Bartter's syndrome in comparison with normal controls (C). No difference in postischemic maximal FBF was found (34.14 +/- 4.67 vs 31.35 +/- 2.86 mL/minute/100 mL), while patients showed a slower recovery after peak flow (PF) (77.57 +/- 61.35 vs 9.42 +/- 3.69 seconds, P < 0.013). Higher plasma endothelin supports the defect in vascular reactivity of Bartter's syndrome already shown for angiotensin II and norepinephrine and is in keeping with the altered intracellular calcium signaling previously demonstrated by the authors in this syndrome. The increased excretion of NO2- and NO3- in this syndrome, together with the higher FRBF and the slower recovery of the FBF and PF, argues in favor of an increased NO synthesis in Bartter's syndrome and of assigning it a role in the vascular hyporeactivity of Bartter's syndrome.

Urinary nitrate excretion is increased in patients with rheumatoid arthritis and reduced by prednisolone

OBJECTIVES

To determine daily production of nitric oxide (NO) measured as urinary nitrate excretion, and the effect of prednisolone in patients with rheumatoid arthritis (RA).

METHODS

Twenty four hour urinary nitrate was measured by gas chromatography in 10 patients with RA, before and two to four weeks after commencement of prednisolone 0.5 mg/kg body weight, and in 18 healthy controls.

RESULTS

Before the start of prednisolone treatment the urinary nitrate excretion in patients with RA was 2.7-fold greater (p < 0.001) than that in healthy volunteers. After prednisolone it decreased significantly, by 28%, at which time inflammatory activity (as indicated by C reactive protein, erythrocyte sedimentation rate, joint count, and early morning stiffness) was also reduced considerably. Despite this decrease, the urinary nitrate excretion in patients with RA remained twice that in the control group (p < 0.05).

CONCLUSIONS

Our data suggest that the endogenous production of NO is enhanced in patients with RA. Furthermore, the results indicate that, in parallel with suppression of inflammation, this increased NO synthesis could be reduced by prednisolone treatment.

Effect of interleukin-4 and interleukin-10 on leucocyte migration and nitric oxide production in the mouse

1. The effect of systemic treatment of mice with murine recombinant interleukin-4 (IL-4) or interleukin-10 (IL-10) on neutrophil infiltration into a specific tissue site and nitric oxide (NO) production from peritoneal macrophages was investigated. 2. Intravenously (i.v.) administered IL-4 (0.01-10 micrograms per mouse, approximately 0.3-300 micrograms kg-1, i.v.) and IL-10 (0.01-1 micrograms per mouse, approximately 0.3-30 micrograms kg-1, i.v.) dose-dependently inhibited neutrophil accumulation into a 6-day-old murine air-pouch induced by local application of interleukin-1 beta (IL-1 beta, 5 ng), with approximate ED50s of 0.35 and 0.90 micrograms, respectively. Neither IL-4 (1 micrograms, 30 micrograms kg-1, i.v.) nor IL-10 (1 micrograms, 30 micrograms kg-1, i.v.) prevented leucocyte accumulation in the mouse air-pouches when interleukin-8 (IL-8, 1 micrograms) was used as chemoattractant. Similarly, neither cytokine had any effect on the in vitro up-regulation of CD11b antigen on the surface of murine circulating neutrophils. 3. Treatment of mice with lipopolysaccharide (LPS, 0.3 mg kg-1, i.p.) caused an increase in the formation of NO (measured as nitrite accumulation) in the supernatant of peritoneal macrophages ex vivo. Pretreatment of mice with IL-4 (0.01-1 micrograms i.v., 20 min before LPS), but not with IL-10 (1 micrograms i.v., 20 min before LPS), caused a dose-dependent reduction in this LPS-stimulated formation of nitrite by peritoneal macrophages ex vivo. 4. Activation of murine macrophages with LPS (1 microgram ml-1 for 24 h) in vitro caused a significant increase in nitrite release in the supernatant of these cells. Pretreatment of either J774.2 or peritoneal macrophages with IL-4 (0.1-1 microg ml-1, 20 min before LPS), but not with IL-1O (1 microg ml', 20 min before LPS) caused a concentration-related attenuation of this LPS-stimulated nitrite formation.5 Thus, both IL-4 and IL-10 inhibit the migration of leucocytes (stimulated by IL-1beta>) in vivo; IL-4 (but not IL-10) inhibits the induction of NO synthase caused by LPS in murine macrophages in vitro and ex vivo.

A mammalian arginine/lysine transporter uses multiple promoters

The mCAT-2 gene encodes a Na(+)-independent cationic amino acid (AA) transporter that is inducibly expressed in a tissue-specific manner in various physiological conditions. When mCAT-2 protein is expressed in Xenopus oocytes, the elicited AA transport properties are similar to the biochemically defined transport system y+. The mCAT-2 protein sequence is closely related to another cationic AA transporter (mCAT-1); these related proteins elicit virtually identical cationic AA transport in Xenopus oocytes. The two genes differ in their tissue expression and induction patterns. Here we report the presence of diverse 5' untranslated region (UTR) sequences in mCAT-2 transcripts. Sequence analysis of 22 independent mCAT-2 cDNA clones reveals that the cDNA sequences converge precisely 16 bp 5' of the initiator AUG codon. Moreover, analysis of genomic clones shows that the mCAT-2 gene 5'UTR exons are dispersed over 18 kb. Classical promoter and enhancer elements are present in appropriate positions 5' of the exons and their utilization results in regulated mCAT-2 mRNA accumulation in skeletal muscle and liver following partial hepatectomy. The isoform adjacent to the most distal promoter is found in all tissues and cell types previously shown to express mCAT-2, while the other 5' UTR isoforms are more tissue specific in their expression. Utilization of some or all of five putative promoters was documented in lymphoma cell clones, liver, and skeletal muscle. TATA-containing and (G+C)-rich TATA-less promoters appear to control mCAT-2 gene expression. The data indicate that the several distinct 5' mCAT-2 mRNA isoforms result from transcriptional initiation at distinct promoters and permit flexible transcriptional regulation of this cationic AA transporter gene.

Hypertension in mice lacking the gene for endothelial nitric oxide synthase

Nitric oxide (NO), a potent vasodilator produced by endothelial cells, is thought to be the endothelium-dependent relaxing factor (EDRF) which mediates vascular relaxation in response to acetylcholine, bradykinin and substance P in many vascular beds. NO has been implicated in the regulation of blood pressure and regional blood flow, and also affects vascular smooth-muscle proliferation and inhibits platelet aggregation and leukocyte adhesion. Abnormalities in endothelial production of NO occur in atherosclerosis, diabetes and hypertension. Pharmacological blockade of NO production with arginine analogues such as L-nitroarginine (L-NA) or L-N-arginine methyl ester affects multiple isoforms of nitric oxide synthase (NOS), and so cannot distinguish their physiological roles. To study the role of endothelial NOS (eNOS) in vascular function, we disrupted the gene encoding eNOS in mice. Endothelium-derived relaxing factor activity, as assayed by acetylcholine-induced relaxation, is absent, and the eNOS mutant mice are hypertensive. Thus eNOS mediates basal vasodilation. Responses to NOS blockade in the mutant mice suggest that non-endothelial isoforms of NOS may be involved in maintaining blood pressure.

Impairment of endothelium-dependent dilation in rabbit renal arteries by oxidized lipoprotein(a). Role of oxygen-derived radicals

BACKGROUND

Hyperlipoproteinemia is associated with impairment of nitric oxide (NO)-mediated, endothelium-dependent dilation in renal arteries. In the present study, we assessed and compared the effects of human lipoprotein(a) and LDL on endothelium-dependent and -independent dilation in vitro.

METHODS AND RESULTS

Dilator responses were detected in isolated, saline-perfused, preconstricted arterial segments by a photoelectric device. Acetylcholine-induced, endothelium-dependent dilator responses of rabbit renal arteries were not significantly attenuated after 150 minutes of incubation with native lipoprotein(a) (30 and 100 micrograms/mL). However, exposure to in vitro oxidized lipoprotein(a) (150 minutes, 30 and 100 micrograms/mL) suppressed acetylcholine-induced dilator responses in a dose-dependent manner. At similar concentrations, native and oxidized LDL had no effect. Endothelium-independent dilations induced by the NO-donor sodium nitroprusside were also impaired by oxidized lipoprotein(a), whereas forskolin-induced dilator responses were unaffected, indicating that smooth muscle dilator capacity was not impaired. Attenuation of dilator responses by oxidized lipoprotein(a) was potentiated in the presence of superoxide dismutase (SOD). The SOD effect was completely blunted by coincubation with catalase (100 U/mL) or deferoxamine. In the absence of SOD, catalase or deferoxamine had no effect on dilator responses. Using a chemiluminescence assay, we could detect increased O2- production by arteries pretreated with oxidized lipoprotein(a), which suggested that enhanced NO inactivation by O2- could be the underlying mechanism for impairment of endothelium-dependent dilations.

CONCLUSIONS

These data indicate that oxidized lipoprotein(a) impairs endothelium-dependent dilation and is more potent than oxidized LDL in this effect. The mechanism of the impairment may involve formation of O2- and inactivation of NO.

Nitric oxide synthase complexed with dystrophin and absent from skeletal muscle sarcolemma in Duchenne muscular dystrophy

Nitric oxide (NO) is synthesized in skeletal muscle by neuronal-type NO synthase (nNOS), which is localized to sarcolemma of fast-twitch fibers. Synthesis of NO in active muscle opposes contractile force. We show that nNOS partitions with skeletal muscle membranes owing to association of nNOS with dystrophin, the protein mutated in Duchenne muscular dystrophy (DMD). The dystrophin complex interacts with an N-terminal domain of nNOS that contains a GLGF motif. mdx mice and humans with DMD evince a selective loss of nNOS protein and catalytic activity from muscle membranes, demonstrating a novel role for dystrophin in localizing a signaling enzyme to the myocyte sarcolemma. Aberrant regulation of nNOS may contribute to preferential degeneration of fast-twitch muscle fibers in DMD.

Association of microvascular leakage with induction of nitric oxide synthase: effects of nitric oxide synthase inhibitors in various organs

Endotoxin (Escherichia coli lipopolysaccharide 0111:B4, 3 mg/kg i.v.) induced the expression of a calcium-independent nitric oxide (NO) synthase, determined after 5 h in cardiac, hepatic, pulmonary and renal tissues, as assessed by the conversion of radiolabelled L-arginine to L-citrulline. This widespread induction of NO synthase in these conscious rats was associated with microvascular injury, as assessed by the vascular leakage of radiolabelled human serum albumin. Concurrent administration of the NO synthase inhibitor. NG-nitro-L-arginine methyl ester (L-NAME, 1-5 mg/kg s.c.) with endotoxin, provoked acute vascular leakage within 2 h in the various organs. By contrast, the delayed injection of L-NAME (1-5 mg/kg s.c.) or NG-monomethyl-L-arginine (12.5-50 mg/kg s.c.) until 3 h after endotoxin challenge inhibited the subsequent microvascular leakage in these organs. These effects of NO synthase inhibitors were reversed by L-arginine (300 mg/kg s.c.) pretreatment. These results support a protective role of constitutive NO synthase in the early phase of endotoxin shock. Such actions contrast with the aggressive actions of the products of inducible NO synthase in the development of widespread microvascular injury in endotoxemic states.

Induction of nitric oxide synthase activity by cytokines in ventricular myocytes is necessary but not sufficient to decrease contractile responsiveness to beta-adrenergic agonists

Recent evidence has documented that increased activity of an inducible nitric oxide synthase (iNOS; type 2 NO synthase) in primary isolates of adult rat ventricular myocytes after exposure to soluble mediators in medium conditioned by lipopolysaccharide-activated macrophages is associated with a decrease in their contractile responsiveness to beta-adrenergic agonists. It remained unclear which specific inflammatory cytokines in this medium contribute to the induction of iNOS activity in myocytes and whether induction of iNOS would result in an obligatory decline in contractile function. Interleukin (IL)-1 beta and tumor necrosis factor-alpha (TNF-alpha) were both present in the lipopolysaccharide-activated macrophage-conditioned medium. However, only IL-1 receptor antagonist and not an anti-rat TNF-alpha antiserum diminished the extent of iNOS induction in myocytes exposed to this medium and prevented a decline in contractile responsiveness to isoproterenol. When recombinant cytokines were used, IL-1 beta, TNF-alpha, and IFN-gamma each induced iNOS activity in cardiac myocytes at 24 hours. However, only the combination of IL-1 beta and IFN-gamma reproducibly caused contractile dysfunction in cardiac myocytes. Among the constituents of the defined medium routinely used for maintenance of adult rat ventricular myocytes in primary culture, it was noted that insulin (10(-7) mol/L) was required for NO production, as detected by nitrite release in cytokine-pretreated myocytes, although insulin had no effect on the extent of induction of iNOS mRNA or maximal enzyme activity in myocyte cell lysates.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of nitric oxide synthase in a model of allergic occupational asthma

We have studied the induction of nitric oxide during late allergic responses, using a guinea pig model of trimellitic anhydride (TMA)-induced airway allergy. TMA is a low molecular weight chemical which can cause occupational asthma. The activity of nitric oxide synthase (NOS) was investigated by the detection of 3H-labeled citrulline formation from 3H-labeled arginine. In sensitized animals, challenge with TMA conjugated to guinea pigs albumin (TMA-GPSA) increased the activity of Ca(2+)-independent NOS (inducible NOS; iNOS) in lung and bronchial tissues at 15-17 h after challenge compared to nonsensitized animals. The induction of iNOS activity was associated with an associated with an increased level of nitrite, an end metabolite of the l-arginine-NO pathway, in bronchoalveolar lavage fluid. In contrast to iNOS, the activity of Ca(2+)-dependent NOS (constitutive NOS; cNOS) was not affected by the allergen challenge. These results demonstrate that iNOS in bronchial tissue is induced late after allergen challenge in sensitized guinea pig.

Immunohistochemical characterization of placental nitric oxide synthase expression in preeclampsia

OBJECTIVE

Our purpose was to compare the expression of endothelial nitric oxide synthase in the placenta and umbilical cord of preeclamptic placenta with that of the normotensive placenta.

STUDY DESIGN

We compared placental endothelial nitric oxide synthase expression in preeclamptic (n = 3) with that in normal (n = 3) pregnancies. Frozen sections of umbilical cords, chorionic plate vessels, and terminal villi were immunostained with a monoclonal endothelial nitric oxide synthase antibody (H32).

RESULTS

No difference in endothelial nitric oxide synthase immunostaining in the endothelium of the umbilical cord artery and vein, chorionic plate vessels, and stem villous vessels was found between preeclamptic and normotensive pregnancies. In contrast, in the preeclamptic placentas endothelial nitric oxide synthase immunostaining was seen in the small terminal villous vessels with underlying smooth muscle layer. In the syncytiotrophoblast endothelial nitric oxide synthase immunostaining appeared primarily apical in location and diffuse in distribution in the preeclamptic placentas but primarily basal and punctate in the normotensive placentas.

CONCLUSIONS

Differences in endothelial nitric oxide synthase expression in terminal villous vessels and in syncytiotrophoblast may be a result of vascular alterations or damage that take place in the placenta in preeclampsia. These differences may alter the regulation of blood flow in the fetal and maternal placental vasculatures in preeclampsia.

The role of increased nitric oxide in the vascular hyporeactivity to noradrenaline in long-term portal vein ligated rats

To test the possible role of nitric oxide production in long-term portal vein ligation in the rat, where the hyperdynamic circulation was reported to be absent, in vivo experiments on isolated thoracic aortic rings from partial portal vein ligated or sham-operated rats were performed, 6 months postoperatively. The concentration-response curves to noradrenaline of both intact and endothelium-denuded rings from portal hypertensive rats were significantly shifted to the right as compared to those from sham-operated animals. In intact rings, addition of NG-nitro-L-arginine, a specific inhibitor of nitric oxide synthase, resulted in a significant shift of the curves to the left in sham-operated and portal vein ligated rats. In endothelium-denuded rings, addition of NG-nitro-L-arginine resulted in a significant shift of the curves to the left in portal vein ligated but not in sham-operated animals. After blockade of the nitric oxide biosynthesis with NG-nitro-L-arginine, the negative logarithm of the concentration of nonadrenaline causing half-maximal response did not significantly differ any more between portal vein ligated and sham-operated rats; in endothelium-denuded rings hyporeactivity to noradrenaline persisted in portal vein ligated rats. Only in the intact rings did NG-nitro-L-arginine significantly increase the maximal contractions. No differences were demonstrated in endothelium-dependent relaxations to acetylcholine between sham-operated and portal hypertensive animals. From these results, it can be concluded that in vitro aortic hyporeactivity to noradrenaline is still present in long-term portal vein ligated rats, and that it results at least partially from activation of the L-arginine: nitric oxide pathway in the aortic vascular wall.

Nitric oxide and ventilatory response to hypoxia

It is believed that hypoxia results in the release of neurotransmitters in the central nervous system, which can excite or inhibit breathing. Recent evidence indicates that nitric oxide (NO) is a physiological messenger molecule that may serve as a neurotransmitter in the CNS. In this study we examined (1) the localization of nitric oxide synthase (NOS) within the nucleus tractus solitarius, and (2) the role of the NO-cGMP pathway in the respiratory response to oxygen deprivation. Nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry was used to determine the distribution of neurons that express NOS, an enzyme involved in NO formation. The NOS inhibitor N omega-nitro-L-arginine was used as tool to assess the NOS activity in the medulla, and to define the role of NO in the respiratory response to acute oxygen deprivation. In the rat and the cat brainstem, histochemical studies showed the presence of NADPH-diaphorase reactive neurons within subnuclei of the nucleus tractus solitarius which receive peripheral chemoreceptor inputs. Chronic pretreatment of rats with N omega-nitro-L-arginine (75 mg/kg, ip, twice daily for 7 days) caused a significant decrease in cGMP, and attenuated the ventilatory response to hypoxia. In anesthetized, paralyzed, vagotomized and artificially ventilated cats with intact carotid sinus nerves (n = 8), administration of N omega-nitro-L-arginine (30-100 mg/kg) attenuated the response to hypoxia, and caused the hypoxia induced roll-off of phrenic nerve activity to occur significantly earlier than when NOS activity was not inhibited. In sinoaortic denervated cats (n=9) blockage of NOS potentiated the decline of the phrenic nerve output. The data suggest that oxygen deprivation leads to activation of NO-cGMP pathway in the central nervous system, which contributes to the induction and maintenance of hypoxia-induced increase in respiratory output. In addition, these findings indicate that NO may inhibit inhibitory synaptic transmission that is triggered by CNS hypoxia, and this is not directly related to peripheral chemoreceptor inputs.

Effect of stress on amino acids and related compounds in various tissues of the rat

The composition of various amino acids and related compounds in the aorta, ventricle, atria, liver, kidney, pancreas, bronchi and adrenals of rats is presented. These patterns are qualitatively similar, but quantitatively different. Stress changed these patterns. In the aorta, alpha-aminobutyric acid and ammonia are decreased. In the ventricle, phosphoserine and red. Glutathione are increased; and ammonia, arginine, asparagine, carnosine, ethanolamine, glutamic acid, glutamine, lysine, phosphoethanolamine and taurine are decreased. In the atria, alpha-aminobutyric acid, aspartic acid, ethanolamine and red. glutathione are increased; and ammonia is decreased. In the liver, alpha-aminobutyric acid, cystine, isoleucine, red. glutathione, methionine and phenylalanine are increased. In the kidney, ethanolamine is increased; and beta - aminobutyric acid, citrulline, cystathionine, glutamic acid, glycine and tryptophan are decreased. In the pancreas, alpha-aminoadipic acid, ox. glutathione, leucine, glutamine, 1-methylhistidine, phenylalanine, phosphoserine, tryptophan and valine are increased; and ammonia, cystine and aspartic acid are decreased. In the adrenal glands, anserine, glutamic acid, glutamine and ox. glutathione are increased; and arginine is decreased. In the bronchi, ethanolamine and beta-alanine are increased and alpha-aminobutyric acid and ox. glutathione are decreased. Thus, stress affects certain amino compounds but changes are substance and tissue specific and independent of changes seen in the plasma.

In acute lung injury, inhaled nitric oxide improves ventilation-perfusion matching, pulmonary vascular mechanics, and transpulmonary vascular efficiency

Acute respiratory distress syndrome continues to be associated with significant morbidity and mortality related to ventilation-perfusion mismatch, pulmonary hypertension, and right ventricular failure. It has been suggested that inhaled nitric oxide, which is a selective pulmonary vasodilator, may be effective in the treatment of acute respiratory distress syndrome; however, the effects of nitric oxide on cardiopulmonary interactions are poorly understood. We therefore developed a model of acute lung injury that mimics the clinical syndrome of acute respiratory distress syndrome. In our model, inhaled nitric oxide significantly reduced pulmonary artery pressure, pulmonary vascular resistance, and pulmonary vascular impedance. In addition, inhaled nitric oxide improved transpulmonary vascular efficiency and ventilation-perfusion matching, which resulted in increased arterial oxygen tension. Although arterial oxygen tension increased, oxygen delivery did not improve significantly. These data suggest that by improving ventilation-perfusion matching and arterial oxygen tension while lowering pulmonary vascular resistance and impedance, nitric oxide may be beneficial in patients with acute respiratory distress syndrome. However, additional measures to enhance cardiac performance may be required.

Spin trapping isotopically-labelled nitric oxide produced from [15N]L-arginine and [17O]dioxygen by activated macrophages using a water soluble Fe(++)-dithiocarbamate spin trap

The unique capabilities of EPR spin trapping of nitric oxide based on a ferrous-dithiocarbamate spin trap have been demonstrated in a study verifying the source of the nitrogen and oxygen atoms in nitric oxide produced from activated macrophages. Spin trapping experiments were performed during nitric oxide generation from activated mouse peritoneal macrophages using the ferrous complex of N-methyl D-glucamine dithiocarbamate as a spin trap. When 15N-substituted arginine was given to the activated macrophages in the presence of the spin trap, a characteristic EPR spectrum of the nitric oxide spin adduct was obtained, which indicates the presence of the 15N atom in the nitric oxide molecule. The hyperfine splitting (hfs) constant of the 15N nucleus was 17.6 gauss. When 17O-containing dioxygen (55%) was supplied to the medium, an EPR spectrum consistent with the 17O-substituted nitric oxide spin adduct was observed in the composite spectrum. The hfs of 17O was estimated to be 2.5 gauss. The 14NO spin adduct observed after prolonged incubation in the medium which contains [15N]L-arginine as the only extracellular source of arginine demonstrates that arginine is recycled through its metabolite in activated macrophages.

Manipulation of the L-arginine-nitric oxide pathway in experimental colitis

The role of the L-arginine-nitric oxide pathway in the pathogenesis of colonic inflammation was assessed using L-arginine and its competitive analogue N omega-nitro-L-arginine methyl ester (L-NAME) in a rat model of colitis. In the first study oral L-arginine 2 per cent (control: 3.4 per cent L-glycine) was administered with and without L-NAME 100 mg/l. Orally administered L-arginine increased colonic inflammation (P = 0.004) and decreased thymic weight (P = 0.0007). Addition of L-NAME reduced the colonic inflammation and prevented loss of body-weight (P < 0.04). In the second study L-NAME was administered orally in concentrations of 100, 200 and 500 mg/l (control: no L-NAME). L-NAME 500 mg/l reduced colonic inflammation and increased thymic weight and body-weight (P < 0.01). Thymic weight and body-weight correlated positively with the concentration of L-NAME administered orally (rs > or = 0.3, P = 0.04). L-NAME l g/l was administered topically as an enema (control: suspension agent). Topical L-NAME reduced colonic inflammation and increased thymic weight (P < 0.05). These results suggest that the L-arginine-nitric oxide pathway mediates colonic inflammation in this model.

Gene therapy for the vulnerable plaque

Acute coronary events result from the rupture of an atherosclerotic plaque, leading to formation of an occlusive coronary thrombus. Recent developments in the field of gene transfer provide the opportunity to genetically modify cells involved in plaque rupture as well as thrombus formation and thus prevent acute coronary syndromes. A first approach consists of transferring genes, the product of which may stabilize the vulnerable plaque by reducing the plaque content in lipids and macrophages. Alternatively, the introduction into the atherosclerotic plaque of genes encoding for thrombolytic proteins or growth factors able to restore physiologic antithrombotic functions of endothelial cells may inhibit thrombus formation should the plaque rupture. The success of such strategies depends on the efficiency with which the transgene is introduced and expressed into the target cell, the duration of transgene expression and the ability of the transgene product to ultimately prevent plaque rupture or thrombus formation, or both.

Tissue engineered perivascular endothelial cell implants regulate vascular injury

Molecular biomaterial engineering permits in vivo transplantation of cells and tissues, offering the promise of restoration of physiologic control rather than pharmacologic dosing with isolated compounds. We engrafted endothelial cells on Gelfoam biopolymeric matrices with retention of viability, normal growth kinetics, immunoreactivity, and biochemical activity. The production of heparan sulfate proteoglycan and inhibition of basic fibroblast growth factor binding and activity by engrafted cells were indistinguishable from endothelial cells grown in culture. Perivascular implantation of Gelfoam-endothelial cell scaffolds around balloon-denuded rat carotid arteries reduced intimal hyperplasia 88.1%, far better than the isolated administration of heparin, the most effective endothelial mimic compound. In concert with a reduction in intimal area, cell proliferation was reduced by > 90%. To our knowledge, there have been no previous reports of extravascular cell implants controlling vasculoproliferative disease. Tissue engineered cells offer the potential for potent methods of vascular growth regulation and insight into the complex autocrine-paracrine control mechanisms within the blood vessel wall.

Reversible binding and inhibition of catalase by nitric oxide

The interactions between nitric oxide (NO), H2O2, and catalase were investigated. H2O2 did not cause detectable breakdown of NO in the absence of catalase, but did cause NO breakdown in the presence of catalase. Catalase bound NO, and NO rapidly and reversibly inhibited catalase with a Ki of 0.18 microM. The significance of these results for NO cytotoxicity is discussed.

The killing of Leishmania major by human macrophages is mediated by nitric oxide induced after ligation of the Fc epsilon RII/CD23 surface antigen

Serum IgE concentrations and the expression of the low-affinity receptor for IgE (Fc epsilon RII/CD23) are increased in cutaneous leishmaniasis or after immune challenge with Leishmania antigens. In vitro, the ligation of CD23 by IgE-anti-IgE immune complexes (IgE-IC) or by anti-CD23 monoclonal antibody (mAb) induces nitric oxide (NO) synthase and the generation of various cytokines by human monocytes/macrophages. The present study shows that IgE-IC, via CD23 binding, induce intracellular killing of Leishmania major in human monocyte-derived macrophages through the induction of the L-arginine:NO pathway. This was demonstrated by increased generation of nitrite (NO2-), the stable oxidation product of NO, and by the ability of NG-monomethyl-L-arginine to block both NO generation and parasite killing. A similar NO-dependent effect was observed with interferon gamma-treated cells. Tumor necrosis factor alpha is involved in this process, since both the induction of NO synthase and the killing of parasites caused by anti-CD23 mAb were inhibited by an anti-tumor necrosis factor alpha mAb. Treatment of noninfected CD23+ macrophages with IgE-IC provided protection against subsequent in vitro infection of these cells by Leishmania major promastigotes. Thus, IgE-IC promote killing of L. major by inducing NO synthase in human macrophages.

Nitric oxide evokes pain at nociceptors of the paravascular tissue and veins in humans

1. Nitric oxide (NO) evokes pain on intracutaneous application, apparently by exciting cutaneous nociceptors. To look for similarities in the responsiveness and sensitivity of other nociceptive systems to NO we determined pain intensity-concentration relations for NO applied to paravascular tissue and veins in humans. 2. NO solutions (0.4-2.0 mM) were either injected paravascularly or perfused through a vascularly isolated hand vein segment. The subjects rated pain continuously with the help of an electronically controlled visual analog scale, which made it possible to determine both the time course (latency, duration) and the intensity of NO-evoked pain. 3. Regardless of where it was applied, at concentrations above 0.7 mM NO always evoked pain of similar time course and concentration dependence. Pain increased proportionally to the concentration of applied NO, reaching subjects' tolerance maximum at four to five times the threshold concentration. 4. Pain intensity-NO concentration relations were congruent, indicating that the respective nociceptive systems are equally sensitive to NO. 5. Our observations are consistent with the hypothesis that NO is a chemical link in peripheral nociception.

Evidence of autocrine modulation of macrophage nitric oxide synthase by alpha-melanocyte-stimulating hormone

alpha-Melanocyte-stimulating hormone (alpha-MSH) is a potent inhibitory agent in all major forms of inflammation. To identify a potential mechanism of antiinflammatory action of alpha-MSH, we tested its effects on production of nitric oxide (NO), believed to be a mediator common to all forms of inflammation. We measured NO and alpha-MSH production in RAW 264.7 cultured murine macrophages stimulated with bacterial lipopolysaccharide and interferon gamma. alpha-MSH inhibited production of NO, as estimated from nitrite production and nitration of endogenous macrophage proteins. This occurred through inhibition of production of NO synthase II protein; steady-state NO synthase II mRNA abundance was also reduced. alpha-MSH increased cAMP accumulation in RAW cells, characteristic of alpha-MSH receptors in other cell types. RAW cells also expressed mRNA for the primary alpha-MSH receptor (melanocortin 1). mRNA for proopiomelanocortin, the precursor molecular of alpha-MSH, was expressed in RAW cells, and tumor necrosis factor alpha increased production and release of alpha-MSH. These results suggest that the proinflammatory cytokine tumor necrosis factor alpha can induce macrophages to increase production of alpha-MSH, which then becomes available to act upon melanocortin receptors on the same cells. Such stimulation of melanocortin receptors could modulate inflammation by inhibiting the production of NO. The results suggest that alpha-MSH is an autocrine factor in macrophages which modulates inflammation by counteracting the effects of proinflammatory cytokines.

Endogenous and exogenous nitric oxide protect against intracoronary thrombosis and reocclusion after thrombolysis

BACKGROUND

Nitric oxide (NO), an endothelium-derived relaxing factor, plays an important role in regulating platelet activation. We evaluated the effect of NO in a canine model of intracoronary thrombosis, thrombolysis, and reocclusion.

METHODS AND RESULTS

Before thrombosis was induced, 34 anesthetized dogs were treated with a continuous intracoronary infusion of saline (n = 8); NG-nitro-L-arginine (L-NNA, n = 8), an inhibitor of NO synthetase; L-arginine (n = 7), the precursor for NO; or sodium nitroprusside (SNP, n = 11), an NO donor. Ten minutes after the infusion was begun, an electric current of 150 microA was applied to the endothelium of coronary arteries to induce thrombosis. Occlusive thrombi developed in all dogs in the saline group (38 +/- 4 minutes) and the L-NNA group (30 +/- 6 minutes), in 6 of 7 dogs in the L-arginine group (81 +/- 18 minutes), and in 6 of 11 dogs in the SNP group (102 +/- 21 minutes) (P < .01). The time to thrombus was prolonged by L-arginine (P < .05) and SNP (P < .01). After 3 hours of thrombus formation in coronary arteries, tissue plasminogen activator and heparin were administered intravenously. Thrombi were lysed in 4 (of 8) dogs in the saline group (71 +/- 8 minutes), in 4 (of 8) dogs in the L-NNA group (72 +/- 8 minutes), in 4 (of 6) dogs in the L-arginine group (50 +/- 14 minutes), and in 4 (of 6) dogs in the SNP group (49 +/- 11 minutes) (P > .05). After thrombolysis, coronary artery reocclusion developed in all reperfused dogs in the saline group (30 +/- 8 minutes) and in the L-NNA group (48 +/- 12 minutes), in 3 (of 4) reperfused dogs in the L-arginine group (123 +/- 26 minutes), and in 3 (of 4) reperfused dogs in the SNP group (128 +/- 19 minutes) (P < .01). The ex vivo platelet aggregation induced by collagen was inhibited after in vivo treatment with L-arginine or SNP.

CONCLUSIONS

Increasing NO production or giving an NO donor may inhibit platelet aggregation and delay intracoronary thrombus formation and reocclusion after thrombolysis.

Nitric oxide and oxygen radicals: a question of balance

The production of superoxide and nitric oxide individually has been associated with the development of several diseases but only recently has it been realised that interactions between them may also be important in disease pathology. The central hypothesis which is emerging is that the balance between nitric oxide and superoxide generation is a critical determinant in the aetiology of many human diseases including atherosclerosis, neurodegenerative disease, ischaemia-reperfusion and cancer. These ideas are discussed in this short overview and placed in the context of the current and future status of therapies which could modulate the balance between nitric oxide and superoxide.

Nitric oxide regulates mitochondrial respiration and cell functions by inhibiting cytochrome oxidase

Nitric oxide (NO) reversibly inhibits mitochondrial respiration by competing with oxygen at cytochrome oxidase. Concentrations of NO measured in a range of biological systems are similar to those shown to inhibit cytochrome oxidase and mitochondrial respiration. Inhibition of NO synthesis results in a stimulation of respiration in a number of systems. It is proposed that NO exerts some of its main physiological and pathological effects on cell functions by inhibiting cytochrome oxidase. Further NO may be a physiological regulator of the affinity of mitochondrial respiration for oxygen, enabling mitochondria to act as sensors of oxygen over the physiological range.

Effects of inhibition of nitric oxide synthesis on TNF alpha serum levels in E. coli endotoxemic rats

We investigated the effects of nitric oxide (NO) synthesis inhibition on mortality rate and TNF alpha serum levels in rats inoculated with E. Coli endotoxin (30 mg/kg i.v.) Pre-treatment of endotoxemic rats with NG-monomethyl-L-arginine (L-NMMA), an inhibitor of NO synthesis by both the constitutive and the inducible isoforms of the NO synthase, did not change the mortality rate but significantly reduced TNF alpha serum levels. By contrast, administration of aminoguanidine, a more specific inhibitor of the inducible NO synthase, did not modify serum TNF alpha. These results suggest that, in E. Coli endotoxemic rats, NO synthetized by the constitutive isoform of the NO synthase positively modulates TNF alpha synthesis.

Lowering of HDL2b by probucol partly explains the failure of the drug to affect femoral atherosclerosis in subjects with hypercholesterolemia. A Probucol Quantitative Regression Swedish Trial (PQRST) Report

The aim of the Probucol Quantitative Regression Swedish Trial (PQRST) (n = 303) was to investigate whether probucol (0.5 g BID) added to diet and cholestyramine (8 g BID) could retard progression or induce regression of femoral atherosclerosis in hypercholesterolemic (> 6.86 mmol/L) subjects. Probucol did not induce regression over the 3-year trial period as estimated by change in lumen volume on quantitative arteriography of a 20-cm segment of the femoral artery. In this report we studied in a representative subgroup (n = 72) whether the reduction in HDL concentrations induced by probucol could explain the failure of the drug to be effective. We analyzed the effects of treatment on HDL particle size subclasses. Probucol lowered the relative level of HDL2b, comprising the largest HDL particles, by 53% and the protein concentration of HDL2b by 67%. The protein reduction in HDL was mainly confined to the apolipoprotein A-I moiety. The change in lumen volume correlated significantly with change in HDL, ie, HDL cholesterol (r = .34, P < .01), HDL2 cholesterol (r = .37, P < .01), HDL2b protein (r = .44, P < .001), and the relative HDL2b value (r = .51, P < .001). The corresponding values for relative HDL2b, distribution calculated on the active (n = 35) and placebo (n = 37) groups separately were also significant (r = .39 and .32, respectively; both P < .05). The correlation between drug-induced change in the relative HDL2b concentration and change in atherosclerosis was independent of the alteration in triglyceride concentration and could not be explained by treatment interaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide suppression of human hematopoiesis in vitro. Contribution to inhibitory action of interferon-gamma and tumor necrosis factor-alpha

IFN-gamma and TNF-alpha, potent inhibitors of hematopoiesis, induce nitric oxide synthase (NOS) in various cell types. When normal human bone marrow (BM) or CD34+ cells were exposed to NO, inhibition of colony formation was dose dependent and direct. NO induced apoptosis in BM progenitors, as shown by electrophoretic detection of DNA degradation and deoxynucleotidyl transferase assay. Using PCR and immunoprecipitation, we found inducible NOS (iNOS) mRNA and iNOS protein in BM after stimulation with IFN-gamma or TNF-alpha. iNOS mRNA was also detected by PCR in highly purified CD34+ cells; TNF-alpha or IFN-gamma increased iNOS expression. The presence of iNOS in CD34+ cells was confirmed in single cells by immunochemical staining. NG-Monomethyl-L-arginine (MM-Arg), an NOS inhibitor, partially reversed the effects of TNF-alpha and, to a lesser extent, IFN-gamma in methylcellulose culture of total BM and CD34+ cells, and inhibited apoptosis of BM cells induced by these cytokines. When the effects of competitive iNOS inhibition were tested on more immature progenitors, MM-Arg increased the number of long-term BM culture-initiating cells in control cultures but failed to protect these cells from the inhibitory action of IFN-gamma and TNF-alpha. Our results suggest that NO may be one mediator of cytokine-induced hematopoietic suppression.

Corticosteroid treatment for sepsis: a critical appraisal and meta-analysis of the literature

OBJECTIVE

To determine the effect of corticosteroid therapy on morbidity and mortality in patients with sepsis.

DATA SOURCES

We searched for published and unpublished research using MEDLINE, EMBASE, and the Science Citation Index, manual searching of Index Medicus, citation review of relevant primary and review articles, personal files, and contact with primary investigators.

STUDY SELECTION

From a pool of 124 potentially relevant articles, duplicate independent review identified nine relevant, randomized, controlled trials of corticosteroid therapy in sepsis and septic shock among critically ill adults.

DATA EXTRACTION

In duplicate, independently, we abstracted key data on population, intervention, outcome, and methodologic quality of the randomized controlled trials.

DATA SYNTHESIS

Corticosteroids appear to increase mortality in patients with overwhelming infection (relative risk 1.13, 95% confidence interval 0.99 to 1.29), and have no beneficial effect in the subgroup of patients with septic shock (relative risk 1.07, 95% confidence interval 0.91 to 1.26). Studies with the highest methodologic quality scores also suggest a trend toward increased mortality overall (relative risk 1.10, 95% confidence interval 0.94 to 1.29). A similar trend was observed for patients with septic shock (relative risk 1.12, 95% confidence interval 0.95 to 1.32). No difference in secondary infection rates was demonstrated in corticosteroid-treated patients with sepsis or septic shock. However, there was a trend toward increased mortality from secondary infections in patients receiving corticosteroids (relative risk 1.70, 95% confidence interval 0.70 to 4.12). The occurrence rate of gastrointestinal bleeding was increased slightly in the treatment group (relative risk 1.17, 95% confidence interval 0.79 to 1.73).

CONCLUSIONS

Current evidence provides no support for the use of corticosteroids in patients with sepsis or septic shock, and suggests that their use may be harmful. These trials underscore the need for future methodologically rigorous trials evaluating new immune-modulating therapies in well-defined critically ill patients with overwhelming infection.

Upregulation and modulation of inducible nitric oxide synthase in rat cardiac allografts with chronic rejection and transplant arteriosclerosis

BACKGROUND

The Lewis-F344 rat cardiac transplantation model produces cardiac allografts with chronic rejection characterized by arteriosclerotic lesions composed of macrophages and smooth muscle cells. Modulation of the inflammatory response with a diet deficient in essential fatty acids protects against the development of intimal thickening. Little is known about the components of the inflammatory response mediating this process. The cytokine-inducible isoform of nitric oxide synthase (iNOS) regulates the high-output nitric oxide pathway that confers activation properties to macrophages and regulates vasomotion, monocyte adherence, and smooth muscle cell proliferation in the vasculature. The purpose of the present study was to determine whether the iNOS pathway was upregulated during the course of chronic cardiac rejection.

METHODS AND RESULTS

We studied iNOS mRNA and protein expression patterns in a series of Lewis-F344 cardiac allografts with early and late chronic rejection and after modulation of the inflammatory response (in an effort to attenuate arteriosclerosis). Relative gene transcript levels were measured with a 32P-dCTP reverse-transcriptase polymerase chain reaction assay designed to amplify iNOS mRNA. The distribution of the iNOS gene product was examined by immunocytochemistry with a polyclonal antibody against iNOS. NOS transcript levels increased significantly in cardiac allografts (days 7, 14, 28, and 75) compared with paired host hearts (exposed to the same circulation) and syngrafts (P < .003). Immunostaining localized the iNOS antigen within subpopulations of mononuclear inflammatory cells in cardiac allografts--presumably, activated macrophages. The number of iNOS-positive mononuclear cells was 25-fold higher in cardiac allografts compared with paired host hearts and syngrafts (P < .009). In cardiac allografts of 75 days or older, there also was striking iNOS staining within some medial and intimal smooth muscle cells in various vessels. Modulation of the inflammatory response (with a diet deficient in essential fatty acids) produced significant decreases in the intimal thickening score and in the percentage of diseased vessels in 28-day cardiac allografts compared with allografts from rats fed a control diet. There was a correlate decrease in iNOS transcript levels and in the number of iNOS-positive mononuclear cells in the 28-day cardiac allografts from rats fed the essential fatty acid-deficient diet.

CONCLUSIONS

The early and persistent upregulation of iNOS in chronic cardiac rejection and the coincident reduction in arteriosclerosis and downregulation of iNOS suggest that this inducible regulator may contribute to the inflammatory response mediating transplant arteriosclerosis.

Serum nitrate levels in ulcerative colitis and Crohn's disease

BACKGROUND

Nitric oxide is an important mediator in inflammatory and autoimmune-mediated tissue destruction and may be of pathophysiologic importance in inflammatory bowel disease. We studied whether serum levels of nitrate, the stable end-product of nitric oxide, are increased in active Crohn's disease or ulcerative colitis, in comparison with quiescent disease and healthy controls. The setting was the gastroenterology unit of the Free University Hospital, Amsterdam.

METHODS

In 146 patients--75 with ulcerative colitis and 71 with Crohn's disease--and 33 controls serum nitrate was measured by the Griess reaction after enzymatic conversion of nitrate to nitrite with nitrate reductase.

RESULTS

Median serum nitrate concentrations did not differ statistically significantly between ulcerative colitis (median, 34.2 mumol/l; range, 15.6-229.4 mumol/l), Crohn's disease (median 32.3 mumol; range 13.2-143.2 mumol/l), and healthy controls (median, 28.7 mumol/l; range, 13.0-108.4 mumol/l). However, when active ulcerative colitis patients (median, 44 mumol/l; range, 29.1-229.4 mumol/l were compared with inactive ulcerative colitis patients (median, 31.2 mumol/l; range, 15.6-59.7 mumol/l), a significant difference in nitrate concentration was found (p < 0.0001). A significant positive correlation was found between serum nitrate levels in ulcerative colitis and erythrocyte sedimentation rate (ESR) (r = 0.30, p - 0.01), leucocyte count (r = 0.27, p = 0.02), and thrombocyte count (r = 0.24, p = 0.04). Comparing active Crohn's disease patients (median, 37.5 mumol/l; range, 13.2-143.2 mumol/l) with inactive Crohn's disease patients (median, 31.3 mumol/l; range, 14.5-92.3 mumol/l) also showed a significant difference in serum nitrate concentration (p < 0.009). Serum nitrate levels correlated with the ESR (r = 0.26, p = 0.028) and serum albumin (r = 0.38, p = 0.004) as well.

CONCLUSION

Nitric oxide production is increased in both active ulcerative colitis and Crohn's disease and may be implicated in the pathogenesis of inflammatory bowel disease.

Measurement of methemoglobin formation from oxyhemoglobin. A real-time, continuous assay of nitric oxide release by human polymorphonuclear leukocytes

We have evaluated the spectrophotometric measurement (at 401 vs. 411 nm) of nitric oxide (NO)-dependent methemoglobin formation from oxyhemoglobin in order to assess NO release from human polymorphonuclear neutrophil leukocytes (PMN). S-nitroso-D,L-acetyl-penicillamine (SNAP, 25-200 microM), a donor of NO, induced a dose-dependent methemoglobin formation. Furthermore, when PMN were activated with N-formyl-methionylleucyl-phenylalanine or phorbol myristate acetate in the presence of superoxide dismutase (SOD) and catalase, methemoglobin formation ensued. The amount of methemoglobin formed was dependent on the amounts of oxyhemoglobin and stimulus used, and the number of PMN in the assay. The NO synthase (NOS) inhibitors NG-monomethyl-L-arginine or nitro-L-arginine methyl ester did not affect methemoglobin generation from oxyhemoglobin induced by SNAP but inhibited that mediated by activated PMN with IC50 values of 250 microM and 340 microM, respectively. The substrate for NO formation from NOS, L-arginine in concentrations up to 1 mM did not significantly influence the methemoglobin formation either induced by SNAP or activated PMN. Exclusion of SOD did not affect SNAP-dependent oxidation of oxyhemoglobin. Exclusion of SOD from the cell-containing system attenuated methemoglobin formation, and if catalase was also excluded the response was further reduced. Finally, PMN from a patient with X-linked chronic granulomatous disease, unable to produce superoxide anions, showed a similar production of methemoglobin from HbO2 as did healthy PMN, activated with the respective agonists. We conclude that spectrophotometric measurement of methemoglobin formation from oxyhemoglobin in the presence of SOD and catalase is a suitable method for the measurement of NO release from PMN, with the benefits of a real-time, continuous assay.

Transcriptional induction of endothelial nitric oxide synthase type III by lysophosphatidylcholine

Endothelial synthesis of NO is catalyzed by constitutive NO synthase type III (NOS-III). NOS-III has been thought to be regulated mainly at the level of enzyme activity by intracellular calcium. We report that in human umbilical vein endothelial cells lysophosphatidylcholine (lyso-PC), a component of atherogenic lipoproteins and atherosclerotic lesions, increases NOS-III mRNA and protein levels. This leads to the augmentation of NOS-III activity and the enhancement of antiplatelet properties of endothelial cells. Importantly, nuclear run-off experiments demonstrate a transcriptional mechanism of regulation of NOS-III expression by lysophosphatidylcholine. As endothelium-derived NO appears to be an anti-atherogenic molecule, induction of NOS-III by lyso-PC may be a protective response that limits the progress of the atherosclerotic lesion and promotes its regression.

Evidence for bidirectional changes in nitric oxide synthase activity in the rat striatum after excitotoxically (quinolinic acid) induced degeneration

Nitric oxide, a gaseous inter- and intracellular messenger, is thought to mediate neurotoxicity via excitatory amino acid receptors which may contribute to the pathogenesis of a variety of neuronal diseases. Excitotoxin lesions induced by quinolinic acid were made unilaterally in the rat striatum to study biochemically, light- and electron microscopically the possible involvement of the nitric oxide synthesizing enzyme nitric oxide synthase in degeneration processes. 5 days after quinolinic acid injection nitric oxide synthase activity in the striatum was elevated to 196.5% (P < 0.005% as compared to controls). There was no requirement of Ca2+ for the enzyme activity measured indicating that the elevation is due to the inducible isoform of nitric oxide synthase. Parallel to the depletion of neurons by quinolinic acid a massive gliosis was seen. Whereas quiescent astroglial cells in the normal striatum did not show any light microscopically detectable nicotinamide adenine dinucleotide phosphate diaphorase reaction, reactive astroglia revealed a substantial labeling distributed over the cell body and their stellar processes. Within the lesion and, particularly, close to the needle tract the number of microglia/macrophages labeled by isolectin B4 increased dramatically. Reactive microglial cells macrophages, situated along the needle tract and characterized by a pseudopodic or a globular shape, contained highest staining activity. At the ultrastructural level only disintegrated, if any, neuronal perikarya were seen five days after quinolinic acid injection while numerous reactive glial cells were observed. Reactive astroglia showed nicotinamide adenine dinucleotide phosphate diaphorase activity by displaying a substantial labeling of the nuclear envelope and endoplasmic membranes. Occasionally stained mitochondria were encountered. Globular-shaped (ameboidal) microglia near the needle tract were rich in phagocytotic debris and, apart from formazan-positive endomembranes, their plasmalemma was often nicotinamide adenine dinucleotide phosphate diaphorase stained. Additionally, in those cells regions of highly electron-dense puncta were seen which differ sharply from other cytoplasmic areas. Such sand-like accumulations of nicotinamide adenine dinucleotide phosphate diaphorase positive grains have never been observed in other cell types, indicating a special type of nitric oxide synthase representation, possibly that of the inducible isoform.

Involvement of inducible nitric oxide synthase in the inflammatory process of myocardial infarction

Inducible nitric oxide synthase (iNOS), which catalyzes the reaction of L-arginine to L-citrulline and nitric oxide (NO), plays an important role in immune-mediated cardiac disorders. The present report summarizes and discusses findings on the induction of NOS in myocardial infarction of rabbits. iNOS was significantly increased in infarcted myocardium 48 h after coronary artery ligation. The effect persisted for 14 days and declined thereafter. Immunohistochemical localization revealed macrophages as a major source of iNOS expression; iNOS expression was also present in infarcted human myocardium. Increased iNOS activity appeared to be related to the induction of apoptosis in infiltrating macrophages and cardiomyocytes. Moreover, preferential inhibition of iNOS by S-methylisothiourea sulfate (SMT) resulted in significant improvement of left ventricular performance and increased regional myocardial blood flow. These findings suggest that selective inhibition of iNOS activity may provide a therapeutic strategy in cardiac disorders such as myocardial infarction.

Nitric oxide inhibits angiotensin II-induced migration of rat aortic smooth muscle cell. Role of cyclic-nucleotides and angiotensin1 receptors

Nitric oxide (NO) and angiotensin II (AII) can effect vascular smooth muscle cell (SMC) proliferation. However, the effects of such agents on SMC migration, an equally important phenomenon with regard to vascular pathophysiology, have received little attention. The objectives of the present study were: (a) to determine whether NO inhibits AII-induced migration of vascular SMCs; (b) to investigate the mechanism of the interaction of NO and AII on SMC migration; and (c) to evaluate the AII receptor subtype that mediates AII-induced SMC migration. Migration of rat SMCs was evaluated using a modified Boydens Chamber (transwell inserts with gelatin-coated polycarbonate membranes, 8 microns pore size). AII stimulated SMC migration in a concentration-dependent manner, and this effect was inhibited by sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP). In the presence of L-arginine, but not D-arginine, IL-1 beta, an inducer of inducible NO synthase, also inhibited AII-induced SMC migration, and this effect was prevented by the NO-synthase inhibitor, N-nitro-L-arginine methyl ester. The effects of NO donors on AII-induced SMC migration were mimicked by 8-bromo-cGMP. Also, the antimigratory effects of SNAP were partially inhibited by LY83583 (an inhibitor of soluble guanylyl cyclase) and by KT5823 (an inhibitor of cGMP-dependent protein kinase). Although 8-bromo-cAMP (cAMP) also mimicked the antimigratory effects of NO donors, the antimigratory effects of SNAP were not altered by 2',5'-dideoxyadenosine (an inhibitor of adenyl cyclase) or by (R)-p-adenosine-3',5'-cyclic phosphorothioate (an inhibitor of the cAMP-dependent protein kinase). Low concentrations of the subtype AT1-receptor antagonist CGP 48933, but not the subtype AT2-receptor antagonist CGP 42112, blocked AII-induced SMC migration. These findings indicate that (a) NO inhibits AII-induced migration of vascular SMCs; (b) the antimigratory effect of NO is mediated in part via a cGMP-dependent mechanism; and (c) AII stimulates SMC migration via an AT1 receptor.

The role of endothelium-derived vasoactive substances in the pathophysiology of exercise intolerance in patients with congestive heart failure

The vascular endothelium releases vasoactive substances that appear to play an important role in the normal regulation of peripheral vasomotor tone. Nitric oxide, endothelins, prostaglandins, and other endothelium-derived vasodilating and vasoconstricting factors are released by the vascular endothelium in response to a diverse array of hormonal, pharmacologic, chemical, and physical stimuli. Shear stress, produced by pulsatile blood flow at the endothelial cell luminal surface, alters endothelial production of several endothelium-derived vasoactive substances, which may contribute to regional regulation of skeletal muscle blood flow during exercise. Abnormal vascular endothelium function has been shown in both experimental and clinical heart failure. Preliminary data suggest that abnormalities of endothelial function may contribute to increased peripheral vasomotor tone during exercise in patients with congestive heart failure.

Effects of immunosuppressive therapy on expression of inducible nitric oxide synthase (iNOS) during cardiac allograft rejection

Recent studies have indicated a role for nitric oxide (NO) in alloimmune responses and in allograft rejection. iNOS mRNA, protein and enzyme activity are induced in myocardium during cardiac allograft rejection. NO produced by iNOS is negatively inotropic and has the potential to be cytotoxic to cardiac myocytes. To investigate whether immunosuppressive agents would alter the expression of iNOS during cardiac allograft rejection, hearts from Wistar-Furth rats were transplanted into the abdomen of Lewis recipients. At day 5 allografts from treated and untreated animals were removed for pathological and biochemical examination. At day 5 the untreated allografts exhibited histological evidence of marked rejection (edema, infiltration with macrophages and lymphocytes, necrosis of cardiac muscle fibers). Abundant iNOS mRNA was apparent in Northern blots and iNOS enzyme activity was increased in ventricular homogenates and in cardiac myocytes purified from the untreated rejecting allografts. Incubation of isolated purified cardiac myocytes from normal rats for 24 h with cytokines known to be present during allograft rejection (IL-1 beta, TNF-alpha and IFN-gamma) was also associated with increased iNOS mRNA and enzyme activity. When Wistar-Furth to Lewis allografts were treated from time of transplantation with FK 506, cyclosporine A, dexamethasone or a combination of all three drugs, histological evidence of rejection and the levels of iNOS mRNA and enzyme activity in ventricular homogenates were reduced significantly below those observed in the untreated allografts. The data in a rat model indicate that immunosuppressive drugs reduce myocardial iNOS mRNA and enzyme activity in rejecting cardiac allografts. The results are consistent with the hypothesis that the alloimmune response and cytokine release are involved in the expression of iNOS during cardiac transplantation rejection.

Severity of hypoxia predicts response to nitric oxide in a porcine pulmonary hypertension model

Although inhaled nitric oxide (NO) has been variably successful in resolving pulmonary hypertension in neonates, children, and adults, no parameters predictive of response to this therapy have been elucidated. We conducted an animal study to determine if severity of hypoxia can predict magnitude and sustenance of response to inhaled NO therapy. Seven Yorkshire swine weighing 11 to 20 kg underwent 16 experiments, each consisting of four phases: Phase 1: Control period of ventilation on FIO2 .3; phase 2: Hypoxic period on FIO2 .10 to .15, establishing pulmonary hypertension; phase 3: Treatment period with NO starting at five parts per million (ppm), doubling dose every 10 min to 80 ppm; phase 4: Posttreatment observation period after discontinuation of NO while maintaining hypoxia for 1 hour or until circulatory failure or pulmonary hypertension of pre-NO magnitude developed. Each animal underwent a maximum of three experiments in random order of hypoxia severity before sacrifice with pentobarbital overdose. Continuous hemodynamic parameters, intermittent cardiac output and pulmonary capillary wedge pressure, and intermittent arterial blood gas analyses were obtained through pulmonary and systemic artery catheters placed by femoral cutdown. Pulmonary and systemic vascular resistances (PVR and SVR) were calculated by standard formulas. Experiments were divided into two groups (n = 8 in each): group 1 with severe hypoxia (PaO2, 25 to 35) and group 2 with moderate hypoxia (PaO2, 36 to 65). Data for all hemodynamic parameters were expressed as mean percentage change from baseline (phase 1) +/- SEM under each set of conditions, and the two groups were compared by two-way analysis of variance and covariance adjusted for order of experimentation.(ABSTRACT TRUNCATED AT 250 WORDS)