Glucocorticoids inhibit the induction of nitric oxide synthase and the related cell damage in adenocarcinoma cells

Oxidative and Nitrosative Stress in Major Depressive Disorder: A Case Control Study

Introduction: The role of increased oxidative stress and alterations to the nitric oxide (NO) pathway have been implicated in major depressive disorder (MDD). The two pathways interact closely with each other but have not been studied simultaneously in MDD. This study aimed to assess and compare the levels of oxidative and nitrosative stress in the neutrophils (PMNs) of drug-naive MDD patients and their first-degree relatives. Methods: 29 drug-naive MDD patients and 27 healthy first-degree relatives and healthy controls aged 18–45 years were included in this study. An assessment of the levels of reactive oxygen species (ROS), nitrites, neuronal NO synthase (nNOS), and myeloperoxidase in PMNs, and cortisol in serum was carried out. Results: Compared to healthy controls, the generation of free radicals, myeloperoxidase activity, and nNOS mRNA expression in PMNs, and cortisol level in serum were significantly higher in drug-naive depression patients. Indeed, increased levels of myeloperoxidase and serum cortisol were also noted in first-degree relatives. The total nitrite content in the PMNs and plasma however was significantly lower in both patients and first-degree relatives. Interestingly, a positive correlation was established in the ROS levels in the PMNs, plasma and neutrophil nitrite, and the serum cortisol level between MDD patients and their first-degree relatives. Conclusion: The results of this study contribute towards a better understanding of the familial association of depressive disorder, and demonstrate for the first time that neutrophil ROS/RNS, plasma nitrite, and serum cortisol levels are positively correlated between MDD patients and their first-degree relatives. However, further studies in larger, more diverse samples are needed to extend these pathways as potential biomarkers to identify persons at high risk for psychopathology at an early stage.

Cortisol regulates nitric oxide synthase in freshwater and seawater acclimated rainbow trout, Oncorhynchus mykiss

Cortisol and nitric oxide (NO) are regulators of ion transport and metabolic functions in fish. In the gill, they show opposite effects on Na⁺/K⁺-ATPase (NKA) activity: cortisol stimulates NKA activity while NO inhibits NKA activity. We hypothesized that cortisol may impact NO production in osmoregulatory tissues by regulating NO synthase (NOS) expression. We evaluated the influence of cortisol treatment on mRNA expression of Nos1 and Nos2 in gill, kidney and middle intestine of both freshwater (FW) and seawater (SW) acclimated rainbow trout and found both tissue- and salinity-dependent effects. Nos2 expression was down-regulated in the gill by cortisol injection in both FW and SW trout. This was substantiated by incubating gill tissue with cortisol ex vivo. Similarly, cortisol injection significantly down-regulated Nos2 expression in kidney of SW fish but not in FW fish. In the middle intestine, Nos2 expression was up-regulated by cortisol injection in FW but unchanged in SW fish. Nos1 expression was up-regulated by cortisol injection in FW kidney and down-regulated in SW kidney, whereas it was unaffected in gill and middle intestine of FW and SW fish. Our data provide the first evidence that cortisol may influence NO production in fish by regulating Nos expression. Indeed, the down-regulation of Nos2 expression by cortisol in the gill may prevent the inhibitory effect of NO on NKA activity thereby furthering the stimulatory effect of cortisol on ion-transport.

Value of fractional exhaled nitric oxide (FE NO) for the diagnosis of pulmonary involvement due to inflammatory bowel disease

BACKGROUND

Pulmonary involvement due to inflammatory bowel disease (IBD) is frequent when evaluating a patient with IBD and pulmonary involvement remains complicated. Most of the patients are asymptomatic and the methods used are mostly invasive or expensive procedures. The aim of this prospective study is to evaluate the value of the fractional exhaled nitric oxide (FE(NO)) level for the diagnosis of pulmonary involvement due to IBD and to investigate any correlation between FE(NO) level and disease activity.

METHODS

Thirty-three nonsmoker patients with IBD (25 ulcerative colitis [UC] and 8 Crohn's Disease [CD]) who were free of corticosteroid treatment and 25 healthy subjects as a control group were enrolled in this study. All patients with IBD were investigated for pulmonary involvement with medical history, physical examination, chest roentgenogram, oxygen saturation, blood eosinophil levels, pulmonary function tests (PFTs), high-resolution computed tomography (HRCT), and FE(NO) level.

RESULTS

Pulmonary involvement was established in 15 patients (45.5%) with IBD. The FE(NO) level was higher in patients with pulmonary involvement than without pulmonary involvement and healthy controls independent from the pulmonary symptoms, eosinophil count, duration of disease, activity of disease, and surgery history (FE(NO): 32 +/- 20; 24 +/- 8; 14 +/- 8 ppb, respectively) (P < 0.05). In addition, diffusion capacity (DLCO) was found to be significantly lower in patients with CD compared with UC (P < 0.05).

CONCLUSIONS

This study showed that an increased FE(NO) level may be used for identifying patients with IBD who need further pulmonary evaluation.

Regulation of NHE3 by nitric oxide in Caco-2 cells

The effect of nitric oxide (NO) on Na+/H+ exchange (NHE) activity was investigated utilizing Caco-2 cells as an experimental model. Incubation of Caco-2 cells with 10(-3) M S-nitroso-N-acetylpenicillamine (SNAP), a conventional donor of NO, for 20 min resulted in a approximately 45% dose-dependent decrease in NHE activity, as determined by assay of ethylisopropylamiloride-sensitive 22Na uptake. A similar decrease in NHE activity was observed utilizing another NO-specific donor, sodium nitroprusside. SNAP-mediated inhibition of NHE activity was not secondary to a loss of cell viability. NHE3 activity was significantly reduced by SNAP (P < 0.05), whereas NHE2 activity was essentially unaltered. The effects of SNAP were mediated by the cGMP-dependent signal transduction pathway as follows: 1) LY-83583 and 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ), specific inhibitors of soluble guanylate cyclase, blocked the inhibitory effect of SNAP on NHE; 2) 8-bromo-cGMP mimicked the effects of SNAP on NHE activity; 3) the SNAP-induced decrease in NHE activity was counteracted by a specific protein kinase G inhibitor, KT-5823 (1 microM); 4) chelerythrine chloride (2 microM) or calphostin C (200 nM), specific protein kinase C inhibitors, did not affect inhibition of NHE activity by SNAP; 5) there was no cross activation by the protein kinase A-dependent pathway, as the inhibitory effects of SNAP were not blocked by Rp-cAMPS (25 microM), a specific protein kinase A inhibitor. These data provide novel evidence that NO inhibits NHE3 activity via activation of soluble guanylate cyclase, resulting in an increase in intracellular cGMP levels and activation of protein kinase G.

The effects of dexamethasone therapy on permeability, blood flow and iNOS expression in experimental glioma

Most studies of dexamethasone (DXN) effects on experimental glioma have used doses 10-500 higher (on mg/kg basis) than those used for patients with brain tumour. The relevance of findings to patients with glioma are therefore uncertain. In order to evaluate the effects of clinical doses of DXN (0.22 mg kg(-1)day(-1)) on the pathophysiology of an experimental glioma we have treated rodents with established C6 gliomas for 3 days. The effects of therapy on local cerebral blood flow (LCBF), tumour blood flow (TBF), tumour capillary permeability (TCP), and inducible nit ric oxide synthase (iNOS) mRNA expression were evaluated. DXN caused a significant reduction in TCP (21 +/- 1.9 to 7.7 +/- 2.2 ml.gm(-1)min(-1)10(-3)) and iNOS mRNA production within and around tumour, but no significant change in either TBF or LCBF. The reduction in TCP was identical to that reported after higher doses of DXN and is probably mediated by glucocorticoid receptors. Further in vivo stud ies using either behavioural or neuropathological paradigms in rodents with established cerebral glioma should be treated with similar doses of DXN to optimise clinical relevance.

Inhibition of microglial nitric oxide production by hydrocortisone and glucocorticoid precursors

Viral and bacterial infection in the central nervous system can induce nitric oxide production, which serves as a major host defense against invading microorganisms. Glucocorticoids secretion is enhanced and immune responses are diminished in stressed animals or in patients suffering depression. Using N9 microglial cells, this study tested the hypothesis that glucocorticoids and their precursors caused an impaired immune defense in animals because these compounds could inhibit microglial nitric oxide production. Results indicated that both hydrocortisone and the synthetic glucocorticoid, dexamethasone, were potent inhibitors of the microglial nitric oxide production. While glucocorticoid precursors were not as potent as hydrocortisone, the potency of these precursors increased linearly as they advanced on the biosynthesis pathway. Northern and Western blot analyses indicated that hydrocortisone and dexamethasone might interfere with the inducible nitric oxide synthase at either the transcription or at the post-translational level, depending on the concentrations used. These results suggest that glucocorticoids have the ability to block nitric oxide production by microgila, which could partially explain the impaired immune protection against infection in the central nervous system in stressed animals.

The involvement of protein kinase C in nitric oxide-induced damage to rat isolated colonic mucosal cells

1 The role of protein kinase C (PKC) in colonic cellular injury in response to high concentrations of nitric oxide (NO) released from the donor, S-nitroso-N-acetyl-DL-penicillamine (SNAP) was investigated. 2 Addition of SNAP (0.1-1000 microM) to the cellular suspension resulted in a dose-dependent increase in the extent of damage to isolated colonic mucosal cells as assessed by Trypan blue dye uptake and release of the lysosmal enzyme, N-acetyl-beta-glucosaminidase. SNAP treatment also resulted in an increase in cellular total PKC activity. These increases were reduced or eliminated by pretreatment of the cells with the PKC antagonists staurosporine or GF 109203X or the NO scavenger, phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). 3 PKC-alpha, PKC-delta, PKC-epsilon and PKC-zeta were detected in colonic cellular lysates by immunoblotting. However, only PKC-epsilon protein was increased in response to SNAP treatment. Furthermore, SNAP treatment resulted in activation of PKC-epsilon by causing translocation of the enzyme from the cytosolic to membrane fraction of the cell. This effect was eliminated if cells were preincubated with the NO scavenger, PTIO. 4 The extent of cellular damage in response to addition of SNAP to the incubation medium was enhanced by coincubation with the PKC activator, phorbol 12-myristate 13-acetate (PMA; 1 and 10 microM). 5 PKC activity and the extent of cell damage in response to SNAP were reduced by preincubation of the cells with the peroxyl scavenger, ebselen (0.01-10 microM). 6 These data suggest that the PKC-epsilon isoform of the enzyme mediates NO-induced damage to colonic mucosal cells. This response may occur, at least in part, due to peroxynitrite formation.

Expressional down-regulation of neuronal-type nitric oxide synthase I by glucocorticoids in N1E-115 neuroblastoma cells

Neuronal-type nitric oxide synthase (NOS I) is involved in ischemia-induced brain damage, and glucocorticoids have been reported to protect from brain damage. This prompted us to investigate if the activity or expression of NOS I was influenced by glucocorticoids. We used the murine neuroblastoma cell line N1E-115 as our experimental model. Short-term incubation (30 min) of the N1E-115 cells with dexamethasone (10 nM to 1 microM) or hydrocortisone (100 nM to 10 microM) did not change the enzymatic activity of NOS I. However, the glucocorticoids inhibited NOS I mRNA expression in a concentration-dependent fashion (down to 53.3 +/- 2. 5% of control). In time-course experiments with 100 nM dexamethasone, maximum down-regulation of NOS I mRNA was seen after 24 hr (55.6 +/- 6.3% of control). Similar effects were seen with 10 microM hydrocortisone. The effect of 100 nM dexamethasone was completely reversed by 1 microM of the glucocorticoid receptor antagonist mifepristone. In experiments with actinomycin D (10 microg/ml), the half-life of the NOS I mRNA was determined to be approximately 12 hr and remained unchanged after glucocorticoid incubation. Nuclear run-on analyses indicated that the decrease in NOS I mRNA was the result of a glucocorticoid-induced inhibition of NOS I gene transcription. In Western blots, the 160-kDa NOS I protein band was down-regulated to 68.5 +/- 8.4% of control after an incubation of the N1E-115 cells with 100 nM dexamethasone for 26 hr. Similarly, NO production was down-regulated to 57.8 +/- 8.7% of control. These data demonstrate that glucocorticoids reduce the expression of NOS I without changing its activity.

Nitric oxide synthesis in myocardium following burn injury in rats

We investigated nitric oxide and cyclic GMP production in myocardium early after burn injury in rats. Nitric oxide synthase activity was measured in cytosol from the left ventricular wall of burned rats. Cytosol from control group animals was shown to contain mainly Ca2+-dependent nitric oxide synthase (cNOS) with a small amount of Ca2+-independent nitric oxide synthase (iNOS). Following burn injury, there was a marked increase in iNOS activity with a peak at 8 h post-burn, however, myocardial cNOS activity was found to decline. Parallel to iNOS induction there was a significant increase in myocardial nitric oxide and cyclic GMP production. All these changes were alleviated by treatment of the rats with dexamethasone. Since increases in cyclic GMP levels in the heart were associated with reduced myocardial contractility, it is possible that enhanced production of nitric oxide by a Ca2+-independent NO synthase accounts, at least in part, for the depression of myocardial contractility seen in burn animals and patients.

Interferon-beta-1-b (IFN-B) decreases induced nitric oxide (NO) production by a human astrocytoma cell line

Inducible nitric oxide synthase (iNOS) is expressed by astrocytes in demyelinating regions of multiple sclerosis (MS) brain plaques, suggesting that NO contributes to MS pathology. Since the immunosuppressive cytokine IFN-B ameliorates MS disease activity, it is of interest to assess the modulatory role of IFN-B on NO production. We studied the effects of IFN-B, as well as dexamethasone, IL-10, and transforming growth factor-beta (TGF-B), on cytokine-induced NO production by the human astrocytoma cell line, A172. L-NMMA and aminoguanidine, competitive inhibitors of iNOS suppressed NO production as measured by the NO byproduct, nitrite, as did IFN-B. Dexamethasone enhanced NO production, and IFN-B decreased the amount of the enhancement. Neither IL-10 nor TGF-B inhibited nitrite production. The therapeutic effect of IFN-B in MS may be partly due to suppression of pathogenic NO production.

Nitric oxide and inflammatory bowel disease: evidence for local intestinal production in children with active colonic disease

BACKGROUND

Active colitis in patients with inflammatory bowel disease is associated with mucosal vasodilation, increased intestinal permeability and abnormal colonic motility. Nitric oxide is a messenger molecule with many functions, including regulation of local blood flow, vasomotor tone, and inflammation. Increased nitric oxide production and inducible nitric oxide synthase activity have been demonstrated in experimental models of colitis. This study was designed to determine the relationship between nitric oxide production and colonic inflammation in children with active colitis and in control subjects and whether expression of inducible nitric oxide synthase protein is demonstrable in the intestinal epithelium of these patients.

METHODS

Nitrate + nitrite were measured in urine, stool, and plasma using the Griess assay. Expression of inducible nitric oxide synthase protein in intestinal tissue was determined by immunohistochemical localization.

RESULTS

Urinary nitrate + nitrite levels were not significantly different in patients and control subjects. In contrast, stool and plasma nitrate + nitrite concentrations were significantly higher in children with inflammatory bowel disease compared with levels in control children (stool: 162.4 +/- 31.0 mumol/l versus 77.2 +/- 22.1 mumol/l; plasma: 65.2 +/- 9.9 mumol/l versus 38.1 +/- 6.6 mumol/L; p < 0.05). Stool nitrate + nitrite levels significantly correlated with plasma values. Immunohistochemical staining of colonic tissue from children with inflammatory bowel disease demonstrated inducible nitric oxide synthase protein located exclusively in epithelial cells.

CONCLUSION

Increased nitric oxide production and enhanced intestinal epithelial cell expression of inducible nitric oxide synthase protein are associated with active colonic inflammation.

Induction of astrocyte argininosuccinate synthetase and argininosuccinate lyase by dibutyryl cyclic AMP and dexamethasone

Arginine is an intermediate in the elimination of excess nitrogen and is the substrate for nitric oxide synthesis. Arginine synthesis has been reported in brain tissue. We have studied the activity of the arginine biosynthetic enzymes argininosuccinate synthetase and argininosuccinate lyase in dexamethasone and/or dibutyryl cyclic AMP treated rat astrocyte cultures. Argininosuccinate lyase activity was stimulated by treatment with either effector and an additive effect was obtained when both agents were added simultaneously. Argininosuccinate synthetase was also increased in dexamethasone treated astrocytes. The effect of dibutyryl cyclic AMP on argininosuccinate synthetase was variable, suggesting a role for additional factors in its regulation as compared to argininosuccinate lyase. Regulation of arginine synthesis in astrocytes may be important to insure that arginine is not limiting for nitric oxide synthesis in neural tissue.

Nitric oxide-induced perturbations in a cell culture model of the blood-brain barrier

The actions of an intracellular nitric oxide generator compound on the properties of a co-culture model of the blood-brain barrier are described. Addition of the iron-sulphur cluster nitrosyl Roussin's black salt (RBS, heptanitrosyl-tri-mu3-thioxotetraferrate (1-)) resulted in a rapid and dose-dependent (50-250 microM) decline in the electrical resistance displayed by co-cultures of vascular endothelial cells and C6 glioma cells. The breach in barrier integrity elicited by RBS (250 microM) could be prevented by either haemoglobin (100 microM), methylene blue (200 microM), or by photon-induced inactivation of RBS. In contrast, the nitric oxide synthase inhibitor nitro-L-arginine methyl ester (250 microM) caused no inhibition in the decline in resistance of RBS-exposed cultures. Addition of 8-bromo-guanosine-cyclic monophosphate (500 microM) did not mimic the actions of RBS. Exposure to intense light of co-cultures manifesting a high transcellular electrical resistance resulted in a reduction in tissue resistance which could be prevented by the presence of haemoglobin (100 microM). We conclude that nitric oxide liberated from RBS results in a reversible diminution in the integrity of the endothelial cell barrier in the co-culture system, and we suggest that light-sensitive endogenous nitric oxide generator compounds may be present in intact cells. Possible roles of nitric oxide in blood-brain-barrier function are considered.

NO chi generation by cultured small intestinal epithelial cells

The effect of cytokines, growth factors, mitogens, and bacterial products on nitric oxide (NO) generation by monolayers of small intestinal epithelial cells-6 (IEC-6) cells was evaluated. Subconfluent IEC-6 cells were maintained in DMEM containing 5% fetal calf serum and after 16-24 hr of incubation, the medium was replaced with fresh medium in the presence or absence of calcium ionophore (CaI), L-NAME, L-NNA, individual growth factors, cytokines, or mitogens. After 72 hr of culture, the media supernatant was collected and NO chi generation was determined. NO synthase activity was determined in sonicated supernatants of IEC-6 cells by [14C] arginine conversion to citrulline. NO chi generation in subconfluent cultures was greater than in fully confluent cultures, suggesting contact inhibition. NO chi generation by IEC-6 cells was significantly increased by CaI and inhibited by L-NAME and L-NNA. LPS, IL-1 beta, IL-2, IL-8, IFN-8, TFN-alpha, EGF, TGF-alpha, bFGF, and PHA significantly increased NO chi generation. NO synthase activity in IEC-6 cells (4.2 +/- 1.7 pmol/min/10(6) cells) was NADPH dependent. These results suggest that stimulation of NO chi generation by intestinal epithelial cells through cytokine bacterial products and mitogens may be one of the mechanisms responsible for their effects in the intestinal tract.

Aminoguanidine inhibits both constitutive and inducible nitric oxide synthase isoforms in rat intestinal microvasculature in vivo

The effects of aminoguanine on the intestinal vascular permeability following endotoxin administration in vivo has been compared to those of the nitric oxide (NO) synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) in the rat. Concurrent administration of aminoguanidine. (12.5-50 mg/kg, s.c.) with endotoxin (E. coli lipopolysaccharide, 3 mg/kg, i.v.), dose dependently increased vascular leakage of radiolabelled albumin in the ileum and colon after 1 h, an effect reversed by the pretreatment with L-arginine (300 mg/kg, s.c.). Aminoguanidine (50 mg/kg, s.c.) also elevated arterial blood pressure over the 1 h investigation period. Similar acute potentiation of endotoxin-provoked vascular injury was observed 1 h following L-NMMA (50 mg/kg s.c.) which also increased blood pressure, indicating the inhibition of constitutive NO synthase. By contrast, administration of aminoguanidine (12.5-50 mg/kg, s.c.) 3 h after endotoxin, at the time of the expression of the inducible NO synthase, reduced the subsequent endotoxin-induced vascular leakage, as did L-NMMA (50 mg/kg). In homogenates of rat ileal or colonic tissue, aminoguanidine inhibited both the constitutive and inducible NO synthase activity showing only 2-fold selectivity for the inducible isoform. Thus, although aminoguanidine inhibits these isoforms of NO synthase, it is not a selective inhibitor of the inducible isoform in the intestinal microvasculature in vivo.

A neutrophil-derived NO-synthase (NOS) inhibitor

In the present work we have demonstrated that the low NOS activity of circulating blood neutrophils is related to an endogenous inhibitory factor. This factor inhibits constitutive NOS (cNOS) of cerebellum and inducible NOS (iNOS) of macrophages in a concentration-dependent manner. Boiling only partially diminished its activity. The inhibition of cNOS was specific, since to some degree NADPH (0.5-4 mM) and more effectively L-arginine (0.1-1 mM), but not D-arginine, reversed the inhibition.

Nitric oxide synthases in mammals

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Evidence that nitric oxide is an endogenous antiangiogenic mediator

1. The involvement of nitric oxide (NO) in the regulation of angiogenesis was examined in the in vivo system of the chorioallantoic membrane (CAM) of the chick embryo and in the matrigel tube formation assay. 2. Sodium nitroprusside (SNP) (0.37-28 nmol/disc), which releases NO spontaneously, caused a dose-dependent inhibition of angiogenesis in the CAM in vivo and reversed completely the angiogenic effects of alpha-thrombin (6.7 nmol/disc) and the protein kinase C (PKC) activator 4-beta-phorbol-12-myristate-13-acetate (PMA) (0.97 nmol/disc). In addition, SNP (28 x 10(-6) M) stimulated the release of guanosine 3'-5'-cyclic monophosphate (cyclic GMP) from the CAM in vitro. 3. In the matrigel tube formation assay, an in vitro assay of angiogenesis, both SNP (1-3 x 10(-6) M) and the cell permeable cyclic GMP analogue, Br-cGMP (0.3-1.0 x 10(-3) M) reduced tube formation. 4. The inhibitors of NO synthase, NG-monomethyl-L-arginine (L-NMMA) (3.8-102 nmol/disc) and NG-nitro-L-arginine methylester (L-NAME) (1.3-34.2 nmol/disc) stimulated angiogenesis in the CAM in vivo, in a dose-dependent fashion. D-NMMA and D-NAME on the other hand had no effect on angiogenesis in this system. 5. L-Arginine (10.9 nmol/disc), although it had a modest antiangiogenic effect by itself, was capable of abolishing the angiogenic effects of L-NMMA (34.2 nmol/disc) and of L-NAME (3.8 nmol/disc). 6. Dexamethasone, an inhibitor of the induction of NO synthase, at 0.2-116.1 nmol/disc, stimulated angiogenesis in the CAM, whereas at 348.4-1161 nmol/disc it inhibited this process. Combination of 38.7 nmol/disc dexamethasone with L-NAME (9.3 nmol/disc) resulted in a potentiation of the angiogenic effect of the former. It appears therefore that both the constitutive and the inducible NO synthase may contribute to the NO-mediated inhibition of angiogenesis. 7. Superoxide dismutase (SOD), which prevents the destruction of NO, at 300 i.u./disc had a modest antiangiogenic effect in the CAM, by itself. In addition, SOD, prevented alpha-thrombin (6.7 nmol/disc) and PMA (0.97 nmol/disc) from stimulating angiogenesis in the CAM.8. These results suggest that NO may be an endogenous antiangiogenic molecule of pathophysiological importance.

Endothelin (ET)-3 stimulates cyclic guanosine 3',5'-monophosphate production via ETB receptor by producing nitric oxide in isolated rat glomerulus, and in cultured rat mesangial cells

We investigated the effects of endothelins on receptor-mediated cyclic nucleotide metabolism in rat glomerulus, inner medullary collecting duct (IMCD), and also in cultured rat glomerular mesangial cells. Endothelin (ET)-3 dose-dependently stimulated cGMP accumulation in glomerulus, which was higher than that of ET-1 or ET-2. ETB receptor agonist IRL 1620 produced cGMP in a dose-dependent manner, mimicking the effect of ET-3. ETA receptor antagonist BQ123-Na did not inhibit ET-3- or IRL 1620-stimulated cGMP generation. NG-monomethyl-L-arginine (L-NMMA) significantly inhibited ET-3- or IRL 1620-induced cGMP production, suggesting that ET-3- or IRL 1620-stimulated cGMP generation was mediated through nitric oxide (NO). Intracellular Ca chelator BAPTA/AM and calmodulin antagonist W-7, but not Ca channel blocker nicardipine, significantly inhibited ET-3- or IRL 1620-induced cGMP generation. In cultured rat mesangial cells, ET-3 stimulated cGMP generation through NO in the presence of fetal calf serum, which was not inhibited by addition of BQ123-Na. In IMCD, ET-3 had no stimulative effect on cGMP generation. We conclude that ET-3 stimulates NO-induced cGMP generation through ETB receptor in glomerulus. This effect seems to be mediated through intracellular Ca/calmodulin, but not through Ca influx via L-type Ca channel. Mesangial cells can be a source of NO coupled to ETB receptor activation in glomerulus. From these results, mesangial ETB receptor may work to counteract the vasoconstrictive effect of endothelin caused via ETA receptor in glomerulus.

The induction of nitric oxide synthase and intestinal vascular permeability by endotoxin in the rat

1. The effect of endotoxin (E. coli lipopolysaccharide) on the induction of nitric oxide synthase (NOS) and the changes in vascular permeability in the colon and jejunum over a 5 h period have been investigated in the rat. 2. Under resting conditions, a calcium-dependent constitutive NOS, determined by the conversion of radiolabelled L-arginine to citrulline, was detected in homogenates of both colonic and jejunal tissue. 3. Administration of endotoxin (3 mg kg-1, i.v.) led, after a 2 h lag period, to the appearance of calcium-independent NOS activity in the colon and jejunum ex vivo, characteristic of the inducible NOS enzyme. 4. Administration of endotoxin led to an increase in colonic and jejunal vascular permeability after a lag period of 3 h, determined by the leakage of radiolabelled albumin. 5. Pretreatment with dexamethasone (1 mg kg-1 s.c., 2 h prior to challenge) inhibited both the induction of NOS and the vascular leakage induced by endotoxin. 6. Administration of the NO synthase inhibitor NG-monomethyl-L-arginine (12.5-50 mg kg-1, s.c.) 3 h after endotoxin injection, dose-dependently reduced the subsequent increase in vascular permeability in jejunum and colon, an effect reversed by L-arginine (300 mg kg-1, s.c.). 7. These findings suggest that induction of NOS is associated with the vascular injury induced by endotoxin in the rat colon and jejunum.

Thirteenth Gaddum Memorial Lecture. Neuronal and endothelium-derived mediators in the modulation of the gastric microcirculation: integrity in the balance

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Cytokines regulate L-arginine-dependent cyclic GMP production in rat glial cells

We have previously demonstrated that primary astrocyte cultures from neonatal rat cortex and C6 glioma cells express a calcium-independent nitric oxide synthase (NOS) on induction with bacterial endotoxin (lipopolysaccharide, LPS). One hypothesis regarding the mechanism of the LPS induction is that it causes release of cytokines from these cells which then induce the enzyme directly. Such cytokine induction of NOS has been demonstrated in many extraneural cell types. L-Arginine-dependent increases in cyclic GMP correlate with smaller increases in accumulation of nitrite, the major oxidation product of nitric oxide, and hence can serve as a more sensitive measure of nitric oxide production. Here we provide evidence that interferon-gamma (IFN-gamma), interleukin (IL)-1 beta and tumour necrosis factor-alpha induce L-arginine-dependent cyclic GMP synthesis in C6 cells and that a combination of IFN-gamma and IL-1 beta induce L-arginine-dependent cyclic GMP synthesis in astrocyte cultures, indicating that these cytokines induce NOS. In both cell types the induction by cytokines was less sensitive to inhibition by dexamethasone, IL-10 and IL-4 than was induction by LPS. These data suggest that cytokines can also induce a NOS in glial cells and that the mechanism of this induction may be more direct than that of LPS, since it is less sensitive to modulation by immunosuppressors. Due to the close associations of astrocytes with neurons and microvasculature, cytokine-induced NOS could have potentially important pathophysiological effects in the central nervous system.

Nitric oxide is involved in the regulation of angiogenesis

The in vivo model of the chick embryo chorioallantoic membrane (CAM) was used to study the involvement of nitric oxide (NO) in angiogenesis. The nitrovasodilator sodium nitroprusside (NaNP) and the amino acid, L-arginine, inhibited angiogenesis, assessed as both collagenous protein biosynthesis and vascular density. NG-monomethyl-L-arginine (L-NMMA), an NO synthase inhibitor, increased both collagenous protein biosynthesis and vascular density, indicating that this agent promotes angiogenesis. These results suggest that NO may participate in the regulation of angiogenesis. Manipulation of NO synthesis therefore, may prove to be another approach for controlling angioproliferative diseases.

The actions of nitric oxide donors in the prevention or induction of injury to the rat gastric mucosa

1. The protective or damaging actions on the gastric mucosa, of locally infused nitrovasodilators that donate nitric oxide (NO), have been investigated in the pentobarbitone-anaesthetized rat. 2. Local intra-arterial infusion of endothelin-1 (ET-1; 5 pmol kg-1 min-1 for 10 min) induced extensive, macroscopically apparent, haemorrhagic injury to the rat gastric mucosa. This damage was dose-dependently reduced by concurrent local intra-arterial infusion of glyceryl trinitrate (GTN; 10-40 micrograms kg-1 min-1) which liberates NO on metabolic transformation, or the nitrosothiol, S-nitroso-N-acetyl-penicillamine (SNAP, 2.5-10 micrograms kg-1 min-1) which spontaneously liberates NO. 3. Local infusion of higher doses of SNAP (20 and 40 micrograms kg-1 min-1, i.a.) did not, however, significantly protect against mucosal injury induced by ET-1. 4. Furthermore, local infusion alone of these higher doses of SNAP, as well as sodium nitroprusside (10-40 micrograms kg-1 min-1, i.a.) which also spontaneously liberates NO, induced significant mucosal injury, as assessed macroscopically and confirmed by histology. 5. Local infusion of these higher doses of SNAP and nitroprusside reduced systemic arterial blood pressure (BP), but this was not correlated with the extent of mucosal injury. 6. Furthermore, local infusion of GTN (10-40 micrograms kg-1 min-1, i.a.) alone, which also reduced BP, failed to induce gastric mucosal damage. 7. These findings suggest that exogenous NO can protect the rat gastric mucosa from damage induced by the vasoconstrictor peptide ET-1, which may reflect local microcirculatory interactions. However, the unregulated release of high levels of NO within the microvasculature induces mucosal injury.

Increased concentrations of nitrite in synovial fluid and serum samples suggest increased nitric oxide synthesis in rheumatic diseases

Cytokines induce nitric oxide synthesis by endothelial cells, macrophages and polymorphonuclear leucocytes, indicating a role for nitric oxide in inflammatory processes. Nitric oxide production was therefore measured indirectly as nitrite in serum and synovial fluid samples from patients with rheumatoid arthritis (RA) and osteoarthritis (OA) together with serum samples from healthy volunteers matched for age and sex. Serum nitrite concentrations in patients with RA and OA were significantly higher than in controls. In both disease groups synovial fluid nitrite was significantly higher than serum nitrite, implying nitric oxide synthesis by the synovium. Serum and synovial fluid nitrite concentrations in RA were also significantly higher than those in OA. These data show increased nitric oxide production in RA and OA and suggest a role for nitric oxide as an inflammatory mediator in rheumatic diseases.

Nitric oxide as a signal in blood vessels

In the five years since the discovery that nitric oxide is produced as a signal in blood vessels, a great deal has been discovered about the processes involved. This article reviews current knowledge about the vascular cell synthesis, effects and subsequent destruction of this messenger molecule.

Restoration of mitochondrial energy-linked reactions following dexamethasone treatment of rats infected with the liver fluke Fasciola hepatica

Mitochondria isolated from male Wistar rats experimentally infected with the common liver fluke, Fasciola hepatica, exhibit loss of respiratory control from 2 weeks post-infection (Rule, et al. (1989) Biochem. J. 260, 517-523). We now report that subcutaneous injections of the anti-inflammatory drug, dexamethasone, during the final week of infection prevented the mitochondrial uncoupling and restored respiratory control almost to the levels of uninfected controls. Further investigations have shown that mitochondria from infected rat livers are unable to synthesize ATP and that abnormal respiration is also evident in hepatocytes isolated from infected rats. These abnormalities were absent when infected rats were treated with dexamethasone. In addition, liver mitochondrial function in infected, congenitally athymic, nude rats (CBH/R nu/nu) was not significantly different from that in uninfected nude or Wistar controls. These results provide evidence that the mitochondrial dysfunction in fascioliasis is host-mediated and that T lymphocytes in particular may be involved.

Induction and potential biological relevance of a Ca(2+)-independent nitric oxide synthase in the myocardium

1. We have investigated whether the myocardium and isolated cardiac myocytes can express a Ca(2+)-independent NO synthase after treatment with endotoxin or cytokines. Nitric oxide synthesis was measured in cytosols from the left ventricular wall from rats treated with endotoxin, or from freshly isolated myocytes from adult rats treated in vitro with cytokines. 2. Cytosols from the ventricle of saline-treated control animals showed only Ca(2+)-dependent NO synthesis. After treatment with endotoxin, the expression of an inducible, Ca(2+)-independent NO synthase was observed. The activity of this enzyme was maximal at 6 h and returned towards control levels by 18 h; no alterations occurred in the Ca(2+)-dependent NO synthase activity. Parallel to this enzyme induction there was an increase in myocardial guanosine 3':5'-cyclic monophosphate (cyclic GMP) and plasma nitrite and nitrate (NOx-). All these changes were prevented by pretreatment of the rats with dexamethasone. 3. Myocytes possessed Ca(2+)-dependent NO synthase activity and expressed, after treatment with tumour necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta), a Ca(2+)-independent NO synthase, the induction of which was prevented by dexamethasone and cycloheximide. 4. Since increases in cyclic GMP levels in the heart are associated with reduced myocardial contractility, it is possible that the enhanced production of NO by a Ca(2+)-independent enzyme accounts, at least in part, for the depression of myocardial contractility seen in septic shock, cardiomyopathies, allograft rejection, burn trauma, as well as during anti-tumour therapy with cytokines.

The role of nitric oxide in endothelial cell damage and its inhibition by glucocorticoids

Incubation of vascular endothelial cells with S.typhosa endotoxin and interferon-gamma caused a time- and concentration-dependent reduction in the viability of the cells. The cytotoxic effect was inhibited in a concentration-dependent manner by NG-monomethyl-L-arginine, an inhibitor of nitric oxide (NO) synthesis, and by the glucocorticoids dexamethasone and hydrocortisone, two inhibitors of the induction of NO synthase. These findings indicate that in these cells the cytotoxic effect of endotoxin is mediated by the NO synthesized by an inducible NO synthase. This induction of NO synthase in vascular endothelial cells may represent a mechanism of local endothelial damage during endotoxin shock and other immunologically based conditions.