Protective Role Of Nitric Oxide Research Articles

Early phase microvascular interactions in rat jejunum between nitric oxide and vasopressin following indomethacin administration

The involvement of endogenous vasopressin in the actions of indomethacin following the concurrent administration of the nitric oxide (NO) synthase inhibitor, NG‐nitro‐L‐arginine methyl ester (L‐NAME), on acute intestinal microvascular permeability has been investigated in the rat. Administration of indomethacin (10 mg/kg, s.c.) or L‐NAME (10 mg/kg, s.c.) alone did not affect jejunal and ileal vascular permeability after 1 h, as determined by the leakage of radiolabelled serum albumin. In contrast, when indomethacin (10 mg/kg, s.c.) was injected concurrently with L‐NAME (2–10 mg/kg, s.c.), significant dose‐dependent plasma leakage occurred in the jejunum. Pretreatment with L‐arginine (300 mg/kg s.c.) 15 min prior to L‐NAME prevented these changes in microvascular permeability. Moreover, pretreatment with the vasopressin pressor‐receptor antagonist, d(CH2)5Tyr(Me)AVP (0.01– 0.2 μg/kg, s.c.) dose‐dependently attenuated such damage. These findings suggest that following indomethacin administration, the early inhibition of NO synthase leads to acute microvascular injury involving vasopressin in the rat jejunum. This suggests a protective role of NO, formed by constitutive NO synthase, counteracting effectively the deleterious actions of endogenous vasopressin.

Early phase microvascular interactions in rat jejunum between nitric oxide and vasopressin following indomethacin administration.

The involvement of endogenous vasopressin in the actions of indomethacin following the concurrent administration of the nitric oxide (NO) synthase inhibitor, NG -nitro-l-arginine methyl ester (l-NAME), on acute intestinal microvascular permeability has been investigated in the rat. Administration of indomethacin (10mg/kg, s.c.) or L-NAME (10mg/kg, s.c.) alone did not affect jejunal and ileal vascular permeability after 1 h, as determined by the leakage of radiolabelled serum albumin. In contrast, when indomethacin (10mg/kg, s.c.) was injected concurrently with L-NAME (2-10mg/kg, s.c), significant dose-dependent plasma leakage occurred in the jejunum. Pretreatment with l-arginine (300 mg/kg s.c.) 15 min prior to l-NAME prevented these changes in microvascular permeability. Moreover, pretreatment with the vasopressin pressor-receptor antagonist, d(CH2 )5 Tyr(Me)AVP (0.01-0.2m̈g/kg, s.c.) dose-dependently attenuated such damage. These findings suggest that following indomethacin administration, the early inhibition of NO synthase leads to acute microvascular injury involving vasopressin in the rat jejunum. This suggests a protective role of NO, formed by constitutive NO synthase, counteracting effectively the deleterious actions of endogenous vasopressin.

Nitric Oxide Inhibited Peroxyl and Alkoxyl Radical Formation with Concomitant Protection against Oxidant Injury in Intestinal Epithelial Cells

A model compound of lipid peroxidation,tert-butyl hydroperoxide (tBOOH), was usedin vitroto investigate (i). the generation of tBOOH-derived peroxyl and alkoxyl radicals by rat intestinal epithelial cells or enterocytes and (ii) the role of nitric oxide (NO) on cell-generated free radical formation and cellular cytotoxicity. Peroxyl, alkoxyl, and methyl radicals were detected and characterized by direct and spin-trapping electron paramagnetic resonance spectroscopy in incubations containing tBOOH and hematin, enterocytes, or intestinal epithelial cell line-6 cells. The direct interactions of tBOOH-derived radicals and NO from nitrosoglutathione (GSNO), nitrosoacetyl penicillamine (SNAP), or 1-{b3-aminopropy-4-(3-aminopropylammonio)} butylamino-diazeniumdiolate (SpNONOate) were demonstrated as their levels were depleted in these incubations. SNAP, not GSNO or SpNONOate, was capable of trapping methyl radical produced during hematin-catalyzed decomposition of tBOOH. Cellular cytotoxicity expressed by percentage of dead cells and lactate dehydrogenase was increased with tBOOH treatment. Addition of GSNO, SNAP, or SpNONOate suppressed tBOOH-induced elevation of cell cytotoxicity. The NO donor precursor glutathione, acetylpenicillamine, or spermine did not have any effects on tBOOH-derived radical generation or cell cytotoxicity. These findings demonstrated free radical–free radical reactions between NO- and tBOOH-derived alkoxyl and peroxyl radicals generated by enterocytes. These reactions, at least in part, describe the protective role of NO from hydroperoxide-induced injury in intestinal epithelial cells.

Protective role of nitric oxide in Staphylococcus aureus infection in mice.

This study was carried out to determine the role of nitric oxide (NO) in Staphylococcus aureus infection in mice. NO production in spleen cell cultures was induced by heat-killed S. aureus. Expression of mRNA of the inducible isoform of NO synthase (iNOS) was induced in the spleens and kidneys of S. aureus-infected mice. When mice were treated with monoclonal antibodies (MAbs) against tumor necrosis factor alpha (TNF-alpha) or gamma interferon (IFN-gamma) before S. aureus infection, the induction of iNOS mRNA expression in the kidneys was inhibited. These MAbs also inhibited NO production in spleen cell cultures stimulated with heat-killed S. aureus. NO production in the spleen cell cultures and levels of urinary nitrate plus nitrite were suppressed by treatment with aminoguanidine (AG), a selective inhibitor of iNOS. The survival rates of AG-treated mice were significantly decreased by either lethal or sublethal S. aureus infections. However, an effect of AG administration on bacterial growth was not observed in the spleens and kidneys of mice during either type of infection. Production of TNF-alpha and IFN-gamma was not affected by AG treatment in vitro and in vivo. These results suggest that NO plays an important role in protection from lethality by the infection, but the protective role of NO in host resistance against S. aureus infection was not proved. Moreover, our results show that TNF-alpha and IFN-gamma regulate NO production while NO may not be involved in the regulation of the production of these cytokines during S. aureus infection.

Protective role of nitric oxide in ocular toxoplasmosis.

To evaluate the role of nitric oxide (NO) in ocular involvement during systemic toxoplasmosis. C57B1/6 mice were infected with Toxoplasma gondii strain ME49. The synthesis of NO was inhibited by an intraperitoneal injection of aminoguanidine every 8 hours, starting on the day of infection. Control infected mice received phosphate buffered saline vehicle alone. After 14 days, the ocular lesions were evaluated by histopathological examination. The expression of NO synthase induced in the spleen by toxoplasma infection was evaluated by immunostaining. The production of NO by the spleen cells of infected mice was measured by the colorimetric assay of Griess in the supernatant of cultures stimulated with toxoplasma antigen or concanavalin A. The inhibition of NO production in T gondii infected mice resulted in a marked increase in the symptoms of ocular inflammation. We observed a strong induction of NO synthase expression in the spleen of infected animals. In culture, the spleen cells from these mice produced high levels of NO in response to T gondii antigens. This elevation of NO synthesis was suppressed in the presence of aminoguanidine. This study indicates that NO plays a crucial role in the protection against T gondii infection as reflected by the severity of the ocular involvement.

A protective role of nitric oxide in isolated ischaemic/reperfused rat heart.

The importance of NO-induced vasodilator tone in maintaining adequate coronary flow to sustain hemodynamic function in aerobically perfused heart and the role of NO in the injury development in ischaemic/reperfused heart was studied. Effect of NO synthesis inhibitor (N omega-nitro-L-arginine, L-NOARG) on isolated working rat hearts subjected to either 90 min of aerobic perfusion or to a global ischaemia (27.5 to 42.5 min) followed by 40 min reperfusion was studied. To overcome coronary flow reducing effect of L-NOARG either perfusion pressure was raised from 75 to 120 cm H2O or adenosine (400 nM) was administered. In the hearts perfused at coronary pressure of 75 and 120 cm H2O, L-NOARG (10 microM) reduced coronary flow by 30% and 17%, respectively, while cardiac output was not affected. Only a transient increase in adenosine and lactate outflow occurred in L-NOARG-treated hearts. The post-ischaemic recovery of functions was impaired in L-NOARG-treated hearts, an effect not correlating with L-NOARG-induced reduction in coronary flow. Although the pre-ischaemic coronary flow was similar in the untreated hearts perfused at 75 cm H2O and in L-NOARG-treated hearts perfused at 120 cm H2O, the post-ischaemic recovery in the latter group was still impaired as compared to that in the untreated hearts. Likewise, coronary flow was similar in the untreated hearts and in those treated with L-NOARG plus adenosine, nevertheless, the post-ischaemic recovery in the latter group was impaired as compared to that in the untreated hearts. While the inhibition of NO synthesis resulted in coronary flow reduction it did not induce a state of permanent ischaemia in isolated rat heart. L-NOARG-induced augmentation of the ischaemia/reperfusion injury was related to the deficit of NO, itself, rather than to the reduction in myocardial perfusion.

A protective role of nitric oxide in isolated ischaemic/reperfused rat heart

A protective role of nitric oxide in isolated ischaemic/reperfused rat heart

Nitric oxide production during murine Lyme disease: lack of involvement in host resistance or pathology

The murine model of Lyme disease was used to determine the role of inflammatory induced nitric oxide (NO) during infection by the spirochete Borrelia burgdorferi. The outer surface lipoproteins of B. burgdorferi are potent stimulators of inflammatory cytokines and NO production by cultured macrophages in vitro. The addition of NO to cultures of B. burgdorferi prevents growth, suggesting a protective role of NO for the infected host. NO is also a crucial effector in some models of arthritis. Therefore, the involvement of NO in controlling B. burgdorferi infection and its participation in pathological development of arthritis were investigated. Both mildly arthritic (BALB/c) and severely arthritic (C3H/HeJ) strains of mice systemically produced high levels of NO 1 week after infection with B. burgdorferi, as determined by urinary nitrate. NO production remained high throughout the infection in BALB/c mice, while in C3H/HeJ mice NO production returned rapidly to uninfected levels. The in vivo inhibitor of the NO synthase enzyme NG-L-monomethyl arginine (LMMA) was given to mice to investigate whether decreasing NO production would alter the course of disease. LMMA effectively blocked NO production in infected mice; however, there was no significant difference in arthritis development, spirochete infection of tissues, or production of specific antibody in LMMA-treated mice. These results indicate that B. burgdorferi is able to persist in the host even in the presence of high levels of NO. Furthermore, NO is not involved in the control of spirochete infection of tissues, nor is it involved in the development of arthritis. The potent activity of NO against intracellular pathogens and the in vivo resistance of B. burgdorferi to NO suggest that this organism is not located in an intracellular compartment during an essential portion of its infection of the mammalian host.

Action of nitric oxide as an antioxidant against oxidation of soybean phosphatidylcholine liposomal membranes

To elucidate the protective role of nitric oxide (NO) against lipid peroxidation, the effect of NO donor on the formation of lipid hydroperoxide and consumption of α-tocopherol in the oxidation of soybean phosphatidylcholine liposomal membranes was studied. The oxidation was induced by either aqueous or lipophilic peroxyl radicals generated by the hydrophilic or lipophilic azo compound, respectively. It was found that NO acted as a potent antioxidant by scavenging peroxyl radicals rapidly. It was also found that NO was capable of penetrating multilamellar membranes to scavenge lipid peroxyl radicals and spare α-tocopherol.

Protective role of NO in hepatic microcirculatory dysfunction during endotoxemia.

Nitric oxide (NO) has been reported to have a protective function in attenuating hepatic injury during endotoxemia or sepsis. As a result, the role of NO in attenuating the hepatic microcirculatory alterations associated with endotoxemia was investigated in mice by in vivo microscopy. The livers were examined 2 h after intravenous injection of Escherichia coli 0111:B4 lipopolysaccharide (LPS) alone or in combination with inhibitors of the synthesis of NO, NG-nitro-L-arginine methyl ester or NG-monomethyl-L-arginine. In the animals treated with the combination of NO synthase inhibitors and LPS, leukocyte adherence was increased threefold above that in animals treated with LPS alone. This was accompanied by a 33% reduction in sinusoidal blood flow. Simultaneous administration of L-arginine, but not D-arginine, eliminated these microcirculatory disturbances. The results demonstrate that inhibition of LPS-stimulated NO production results in an early hepatic microvascular inflammatory response to a dose of endotoxin which by itself is scarcely inflammatory. This suggests that NO plays a significant role in stabilizing the hepatic microcirculation during endotoxemia, thereby helping to protect the liver from ischemia and leukocyte-induced oxidative injury.

A protective role for nitric oxide in the oxidative modification of low density lipoproteins by mouse macrophages

Low density lipoproteins (LDL) oxidatively modified by macrophages have been shown to be atherogenic in ex vivo studies. We studied the potential role of nitric oxide (NO), a free radical produced by macrophages, in LDL modification. Human LDL (1 mg/ml) were incubated with mouse peritoneal macrophages in Ham's F-10 medium. The cells were then stimulated by interferon-γ and tumor necrosis factor-α to increase their production of NO from 1.3 to 12.2 μM in 24 h, as measured by nitrite. Lipid peroxidation of LDL, as measured by thiobarbituric acid-reactive materials (TBARS), was reduced in stimulated cells in a time-dependent manner. At 24 h, the decrease was about 27%. In the presence of an NO synthase inhibitor (N o-aminophomoarginine), the generation of NO was diminished and the protection against LDL lipid peroxidation was reversed. The extent of LDL protein modification was also assessed by examining its electrophoretic mobility. It was found that macrophage NO reduced the change in LDL electromobility. These data indicate that the production of NO may inhibit the oxidative modification of LDL with cytokine-stimulated macrophages. We suggest that NO plays a protective role in limiting macrophage-induced LDL modification.