Nitric oxide in inflammation and immune response

Experimental Autoimmune Encephalomyelitis Is Exacerbated in Mice Lacking the NOS2 Gene

Nitric oxide is believed to be a prominent mediator of inflammation based in part on the correlative expression of the inducible nitric oxide synthase (iNOS) gene in various pathologies. The resulting high output of the highly reactive molecule nitric oxide is then believed to play an important role in the evolving inflammatory response. Studies have shown that iNOS and nitric oxide are present in the tissues of patients with multiple sclerosis (MS). In rodent models of MS, experimental autoimmune encephalomyelitis (EAE), it has been shown that nonspecific NOS inhibitors partially ameliorate the disease. To determine the importance of iNOS in this model of MS, we induced EAE in mice containing a disrupted iNOS (NOS2) gene. Surprisingly, by day 24, the NOS2 knockout mice had a greater incidence of EAE than wild-type control mice (75 vs 12%), and had a higher average severity score (2.42 vs 0.44). These differences appear to result largely from the failure of the disease to remit in NOS2 KO mice. Wild-type mice have a profound ability to reverse EAE (82%) compared with the knockout mice (19%). This result implies that iNOS may in some instances play a protective role in autoimmune-mediated tissue destruction.

Therapeutic effects of nitric oxide inhibition during experimental fecal peritonitis: role of interleukin-10 and monocyte chemoattractant protein 1

This study demonstrates that the therapeutic effect of a nitric oxide inhibitor in a murine model of fecal peritonitis is mediated in part by increased levels of interleukin-10 (IL-10) and monocyte chemoattractant protein 1 (MCP-1). Female CD1 mice were subjected to cecal ligation and puncture (CLP) with a 21-gauge needle and, immediately following surgery, were injected intraperitoneally with saline, N(G)-nitro-L-arginine methyl ester (L-NAME; 8 mg/kg), or N(G)-nitro-D-arginine methyl ester (D-NAME; 8 mg/kg). At 96 h after surgery and drug treatment, 20% of mice that received D-NAME had survived whereas 60% of mice that received L-NAME were alive. To elucidate the effect of L-NAME treatment on chemokine and cytokine production during fecal peritonitis, the levels of macrophage inflammatory protein 2 (MIP-2), IL-10, and MCP-1 were measured in peritoneal washings from additional groups of mice 24 h after the CLP surgery. Peritoneal fluids from L-NAME-treated mice contained significantly higher levels of IL-10 and MCP-1 than did those from D-NAME-treated mice. To elucidate the effect of nitric oxide inhibition on potential cellular sources of IL-10 and MCP-1 in the CLP model, cultured alveolar and peritoneal macrophages were activated with bacterial lipopolysaccharide in the presence of L-NAME; these macrophages produced significantly more MCP-1 than did similarly activated macrophages in the presence of D-NAME. In the CLP surgery model, immunoneutralization of IL-10 alone or IL-10 and MCP-1 together with polyclonal antibodies prior to surgery significantly reduced the survival rates in L-NAME-treated groups compared with L-NAME-treated groups that received preimmune serum. Taken together, these data demonstrate that the inhibition of nitric oxide following experimental CLP fecal peritonitis is therapeutic, in part through the modulatory effect of this treatment on the synthesis of IL-10 and MCP-1.

Effect of methylguanidine, guanidine and structurally related compounds on constitutive and inducible nitric oxide synthase activity

The inhibitory activity of methylguanidine, guanidine and their precursors, creatine and creatinine, on both the neuronal constitutive and lung inducible isoforms of nitric oxide synthase were examined in this study. Methylguanidine and guanidine (0.01-3 mM) significantly (P<0.01) inhibited in a concentration-dependent manner both isoforms of the enzyme. Furthermore analysis of the inhibition curves by ANOVA revealed that methylguanidine and guanidine act as non selective inhibitors of both nitric oxide synthases (P>0.4 for both methylguanidine and guanidine). In contrast, creatine and creatinine, although containing guanidine group, were totally ineffective on either enzyme even at concentration up to 3 mM. The results obtained for tested compounds also suggest a role for the lateral chain of guanidine group in the enzyme inhibition. The lack of selectivity of methylguanidine and guanidine in inhibiting both the nitric oxide synthase enzymes could account for some pathological manifestations like neurological disorders, host defense impairment and probably hypertension, that often occur in patients with uremia or chronic renal failure.

Genetic contribution of the endothelial constitutive nitric oxide synthase gene to plasma nitric oxide levels

Nitric oxide (NO) has an important physiological role in regulating vascular tone and is also relevant to many pathological processes including hypertension and atherosclerosis. Endothelial constitutive nitric oxide synthase (ecNOS) is the key enzyme in determining basal vascular wall NO production. We used a combination of maximum-likelihood-based statistical genetic methods to explore the contributions of the ecNOS gene and other unmeasured genes to basal NO production measured by its metabolites (NOx: nitrite and nitrate) in 428 members of 108 nuclear families. Our initial quantitative genetic analysis estimated that approximately 30% of the variance in fasting NOx levels is due to genes (chi 2(1) = 16.04, P = .000062). Complex segregation analysis detected the effects of both a single locus and residual polygenes on NOx levels, and measured genotype analysis showed that plasma NOx levels in those homozygous for the rare allele (64.9 +/- 7.8 mumol/L) were significantly higher (P = .000242) than those homozygous for the common allele (30.2 +/- 3.1 mumol/L). The results of the variance component linkage analysis were consistent with linkage of a quantitative trait locus in or near the ecNOS gene to variation in plasma NOx levels (P = .0066). While many environmental factors have been shown to alter transiently plasma NOx levels, our study is the first to identify a substantial effect of the ecNOS locus on the variance of plasma NOx, i.e. basal NO production. This finding may be relevant to atherogenesis and NO-related disorders.

Inhibition of human lymphocyte proliferation by nitric oxide-releasing oxatriazole derivatives

The effects of novel nitric oxide (NO)-releasing oxatriazole derivatives GEA 3162 and GEA 3175 were studied on cell proliferation and cGMP synthesis in human peripheral blood mononuclear cells stimulated with a lectin mitogen concanavalin A. GEA 3162 (1-30 microM) and GEA 3175 (3-30 microM) inhibited mononuclear cell proliferation in a dose-dependent manner being more potent than the earlier known NO-donor S-nitroso-N-acetylpenicillamine. The inhibitory action was more pronounced when submaximally stimulating concentrations of concanavalin A (0.1 and 1 microg/ml) were used and no inhibition was seen when concanavalin A concentrations were increased up to 10 microg/ml. The antiproliferative concentrations of GEA 3162, GEA 3175 and S-nitroso-N-acetylpenicillamine induced a rapid and transient increase in cGMP production in mononuclear cells cultured in the presence of concanavalin A. Both the antiproliferative action and the increased cGMP production were attenuated when red blood cells were added into the cultures indicating that NO is responsible for both of these actions. An analogue of cGMP, 8-bromo-cGMP (0.1-3 mM) reduced concanavalin A-induced proliferation in a dose-dependent manner suggesting that cGMP may be involved in the antiproliferative action of NO-donors. NO-releasing compounds have immunosuppressive actions which offer therapeutic possibilities and should be kept in mind as potential adverse events when these compounds are used in other indications.

Role of nitric oxide in the physiopathology of pain

Many painful disorders, including joint dysfunctions such as rheumatoid arthritis (RA) or temporomandibular joint disorders (TMD), are associated with hyperthermia of the overlying skin. The same is true of certain intractable chronic pain conditions, such as chronic orofacial pain, which may be associated with TMD. We suggest that this skin hyperthermia, caused by regional vasodilation, is induced by extravascular nitric oxide (NO). Extravascular NO can be produced in the affected joint by osteoblasts, chondrocytes, and macrophages, by mechanical stimulation of endothelial cells, or by stimulated neurons. In view of a strong correlation between pain and skin hyperthermia in these disorders, and the evidence that NO enhances the sensitivity of peripheral nociceptors, we also suggest that at least this kind of pain is associated with excessive local level of NO. This hypothesis can be verified by dynamic area telethermometry, assessing the effect of NO on the sympathetic nervous function. This mechanism, which is in line with the general role of NO as a mediator between different organ systems, also may be relevant to any pain associated with enhanced immune response. Clinical implications of the proposed mechanism are discussed.

Nitric oxide synthase activity and endothelial ultrastructure in ischaemic skin-flaps

The aim of the present study was to detect and quantify nitric oxide synthase (NOS) activity and to investigate morphological changes in the endothelium in two different ischaemic dorsal flap models in the rat, one based cranially and one based caudally. Intact skin from the dorsum was used as control. In both groups flaps were removed at 1, 4, 12, 24 and 72 h after surgery respectively. NOS-activity was measured by the conversion of L-arginine to L-citrulline and endothelial morphology was investigated using transmission electron microscopy. Intact skin showed Ca(2+)-dependent but no Ca(2+)-independent NOS-activity. A time-dependent decrease in Ca(2+)-dependent NOS-activity was seen in the proximal and distal part of the flaps in both flap models and was most pronounced in the distal part. Ca(2+)-independent NOS-activity increased in the proximal and distal part of flaps based cranially and in the proximal part of flaps based caudally. Morphological analysis of the endothelium showed signs of endothelial damage including blebbed membranes, swelling and endothelial loss. These findings show that ischaemia caused by skin-flap surgery leads to endothelial damage and a decrease in Ca(2+)-dependent nitric oxide synthase activity. Furthermore, in the skin-flaps an induction of Ca(2+)-independent nitric oxide synthase (iNOS) activity was noted both in surviving flap tissue and in flap tissue destined to necrose.

Pulmonary hypertension and systemic vasoconstriction may offset the benefits of acellular hemoglobin blood substitutes

OBJECTIVE

We tested the hypothesis that the pharmacologic properties of a small volume of alpha alpha-cross-linked hemoglobin (alpha alpha Hb) could effectively resuscitate pigs subjected to hemorrhage.

METHODS

Fourteen pigs hemorrhaged to a mean arterial pressure (MAP) of 40 mm Hg for 60 minutes were treated with a 4-mL/kg 2-minute infusion of 10 g/dL alpha alpha Hb or 7 g/dL human serum albumin, an oncotically matched control solution.

RESULTS

The removal of blood (17 +/- 1.5 mL/kg) caused the typical physiologic responses to hemorrhagic hypovolemia. Infusion of alpha alpha Hb restored mean arterial pressure and coronary perfusion pressure, but cardiac output and mixed venous O2 saturation did not improve significantly. Pulmonary arterial pressure and pulmonary vascular resistance increased markedly and were higher than baseline levels after alpha alpha Hb. Infusion of human serum albumin produced only minor hemodynamic changes. Brain blood flow did improve to baseline values after alpha alpha Hb, but was the only tissue to do so. In the human serum albumin group, superior mesenteric artery blood flow recovered to baseline values, whereas brain blood flow did not. Blood flows to other tissues were similar in both groups.

CONCLUSION

Small-volume infusion of alpha alpha Hb restored mean arterial pressure and brain blood flow, but pulmonary hypertension and low peripheral perfusion may offset benefits for trauma patients.

3-Morpholino-sydnonimine-induced suppression of human neutrophil degranulation is not mediated by cyclic GMP, nitric oxide or peroxynitrite: inhibition of the increase in intracellular free calcium concentration by N-morpholino-iminoacetonitrile, a metabolite of 3-morpholino-sydnonimine

This study was designed to clarify the mechanism of the inhibitory action of a nitric oxide (NO) donor 3-morpholino-sydnonimine (SIN-1) on human neutrophil degranulation. SIN-1 (100-1000 microM) inhibited degranulation (beta-glucuronidase release) in a concentration-dependent manner and concomitantly increased the levels of cGMP in human neutrophils in suspension. However, further studies suggested that neither NO nor increase in cGMP levels were mediating the inhibitory effect of SIN-1 on human neutrophil degranulation because 1) red blood cells or 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl added as NO scavengers did not inhibit the effect; 2) inhibitors of cGMP synthesis (methylene blue) or phosphodiesterases (3-isobutyl-1-methylxanthine) did not produce changes in cell function correlating with the changes in cGMP. SIN-1 releases both nitric oxide and superoxide, which together form peroxynitrite. Chemically synthesized peroxynitrite (1-100 microM) did not inhibit, but at high concentrations (1000-2350 microM), it potentiated FMLP-induced beta-glucuronidase release from neutrophils. Thus formation of peroxynitrite from SIN-1 does not explain its inhibitory effects on neutrophil degranulation. The NO-deficient metabolite of SIN-1, SIN-1C (330-1000 microM) inhibited human neutrophil degranulation in a concentration-dependent manner similar to that of SIN-1 and reduced the increase in intracellular free calcium induced by N-formyl-L-methionyl-L-leucyl-L-phenylalanine. C88-3934 (330-1000 microM), another NO-deficient sydnonimine metabolite, also inhibited human neutrophil degranulation. In conclusion, the data shows that the NO-donor SIN-1 inhibits human neutrophil degranulation in a cGMP-, NO-, and peroxynitrite-independent manner, probably because of the formation of more stable active metabolites such as SIN-1C. The results demonstrate that studies on the role of NO and/or peroxynitrite carried out with SIN-1 and other NO-donors should be carefully re-evaluated as to whether the effects found are really attributable to NO or peroxynitrite and that in future studies, it will be crucial to carry out control experiments with the NO-deficient metabolites in any studies with sydnonimine NO-donors.

Effect of late modulation of nitric oxide production on murine lupus

MRL/MpJ-Faslpr (MRL-lpr) and New Zealand Black/ White (NZB/W) mice develop spontaneous autoimmune disease characterized by autoantibody production and glomerulonephritis that progresses in parallel with increasing systemic nitric oxide (NO) production. A previously published study from our laboratory indicated that oral administration of the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (NMMA) before the onset of clinical disease significantly decreased renal and joint pathology in MRL-lpr mice. To characterize the effect of late modulation of NO production in murine SLE, we administered oral NMMA and/or restricted dietary arginine after disease onset in two murine models of SLE. When receiving combined NMMA and arginine restriction, MRL-lpr mice had reduced joint pathology scores and NZB/W mice had lower renal pathology scores than control mice. These results indicate that modulating NO production after the onset of disease diminishes disease severity in two models of SLE, although not as effectively as treating before disease onset.

Nitric oxide increases tumor necrosis factor production in differentiated U937 cells by decreasing cyclic AMP

Nitric oxide (NO) increases tumor necrosis factor (TNF) synthesis in human peripheral blood mononuclear cells by a cGMP-independent mechanism. NO has been shown to inhibit adenylate cyclase in cell membranes. Since cAMP down-regulates TNF transcription, we examined the possibility that NO enhances TNF synthesis by decreasing cAMP. U937 cells were induced to differentiate using phorbol myristate acetate (100 nM for 48 h) and then were incubated for 24 h with sodium nitroprusside (SNP) or S-nitroso-N-acetylpenicillamine (SNAP). These NO donors increased TNF production (7.0- and 15.6-fold, respectively, at 500 microM) in a dose-dependent manner (p = 0.002). However, SNP and SNAP did not elevate cGMP levels in U937 cell cultures, and the cGMP analog, 8-bromo-cGMP, had no effect on TNF production. In contrast, SNP (p = 0.001) and SNAP (p = 0.009) decreased intracellular cAMP levels by up to 51.5% over 24 h and, in the presence of a phosphodiesterase inhibitor, blunted isoproterenol-stimulated increases in cAMP by 21.8% (p = 0.004) and 27.6% (p = 0.008), respectively. H89, an inhibitor of cAMP-dependent protein kinase, dose dependently increased TNF production in phorbol myristate acetate-differentiated U937 cells in the absence (6.5-fold at 30 microM; p = 0.035), but not in the presence (p = 0.77) of SNAP. Conversely, the cAMP analog dibutyryl cAMP (Bt2cAMP) blocked SNAP-induced TNF production (p = 0.001). SNP and SNAP (500 microM) increased relative TNF mRNA levels by 57.5% (p = 0.045) and 66.2% (p = 0.001), respectively. This effect was prevented by Bt2cAMP. These results indicate that NO up-regulates TNF production by decreasing intracellular cAMP.

Endogenous nitric oxide and prostaglandin E2 do not regulate the synthesis of each other in interleukin-1 beta-stimulated rat articular cartilage

Increased levels of nitric oxide (NO) and prostaglandins (PG) are present in the synovial fluid from patients with rheumatoid arthritis and osteoarthritis. Interleukin-1 beta (IL-1) has been shown to induce the synthesis of both of these mediators. The present work was designed to study the interactions of NO and PGE2 synthesis induced by IL-1 in rat articular cartilage. Incubation of intact cartilage with IL-1 resulted in different dose response curves for NO and PGE2 synthesis. Two inhibitors of nitric oxide synthase N-monomethyl-L-arginine (L-NMMA) and L-N-iminoethylornithine, (L-NIO), abolished the IL-1-induced nitrite production but failed to have any influence on the PGE2 synthesis. Exogenous NO, produced by two chemically different NO-releasing compounds (SIN-1 and GEA 3175) had no effect on PGE2 synthesis in articular cartilage. Dexamethasone and ketoprofen inhibited IL-1 induced PGE2 production, while nitrite synthesis remained unaltered. Acetylsalicylic acid (ASA) reduced PGE2 synthesis and had a slight inhibitory action also on NO production. In conclusion, our results show, that IL-1 induces the synthesis of both PGE2 and NO in articular cartilage but these two inflammatory mediators are not mediating the synthesis of one another.

Anaerobic production of alginate by Pseudomonas aeruginosa: alginate restricts diffusion of oxygen

Pseudomonas aeruginosa produced alginate and elevated algD (encoding GDPmannose 6-dehydrogenase) transcription under strict anaerobic conditions, especially when using nitrate as a terminal electron acceptor. Purified alginate added to bacterial suspensions caused a decrease in growth, suggesting that alginate contributes to oxygen limitation for the organism and likely for patients afflicted with the inherited autosomal disease cystic fibrosis.

Nitric oxide-donating properties of mesoionic 3-aryl substituted oxatriazole-5-imine derivatives

1. The nitric oxide (NO)-releasing properties of two new mesoionic 3-aryl substituted oxatriazole-5-imine derivatives (GEA 3162 and GEA 3175) were characterized and compared with the known NO-donors 3-morpholino-sydnonimine (SIN-1) and S-nitroso-N-acetylpenicillamine (SNAP). 2. GEA 3162, GEA 3175, SIN-1 and SNAP inhibited adenosine 5'-diphosphate-induced platelet aggregation (IC50 values 0.18, 0.39, 3.73 and 2.12 microM, respectively). All four compounds induced a dose-dependent and more than 4 fold increase in cyclic GMP in platelets. The increase in cyclic GMP concentration was potentiated more than 1.5 fold by a phosphodiesterase inhibitor, zaprinast (10 microM) and inhibited 38-97% by oxyhaemoglobin (10-45 microM). 3. All of the four compounds studied converted oxyhaemoglobin to methaemoglobin and formed a paramagnetic NO-haemoglobin complex. All but GEA 3175 formed nitrite and nitrate in phosphate buffer. During a 40 min incubation, GEA 3162, SIN-1 and SNAP (100 microM) produced 50-70 microM NO2- + NO3- as determined by high performance liquid chromatography. The release of NO and NO2 by GEA 3175 was increased 140 fold in the presence of human plasma (0.14 and 19.7 ppb in the absence and presence of 1% human plasma, respectively) as analyzed by ozone chemiluminescence. 4. The results suggest that the mesoionic 3-aryl substituted oxatriazole-5-imine derivatives GEA 3162 and GEA 3175 as well as SIN-1 and SNAP release nitric oxide.