RESUMO
We identified the source of the nitrogen included into nitric oxide (NO) and studied the relationship between formation of NO, intracellular dinitrosyl ferrous iron complex (DNIC) and release of nitrite by murine bone-marrow-derived macrophages stimulated with E. coli lipopolysaccharide (LPS). NO was trapped in the cell membrane by iron-diethyldithiocarbamate complex (FeDETC) and was detected as a paramagnetic NOFe(DETC)2 complex by electron paramagnetic resonance (EPR) spectroscopy. Macrophages stimulated for 7 h up to 48 h with LPS and then incubated for 2 h with DETC exhibited an anisotropic EPR signal of axial symmetry with g-factor values g perpendicular = 2.035, g parallel = 2.02 and a triplet hyperfine structure (hfs) at g perpendicular characteristic for NOFe(DETC)2. In cells incubated with [15NG]L-arginine instead of [14NG]L-arginine the EPR signal of [15N]OFe(DETC)2 was detected with a doublet hfs at g perpendicular, indicating that NO was generated exclusively from the terminal guanidino-nitrogen of extracellular L-arginine. The ratio of NO formation and of nitrite release changed with time of exposure to LPS, nitrite exceeding NO at early stages of macrophage activation, and NO exceeding nitrite at later stages. DNIC with thiolate ligands (0.5 nmol/10(7) cells) was observed in stimulated macrophages not loaded with DETC. Furthermore, DNIC released from macrophages was trapped in the extracellular medium by bovine serum albumin (BSA) (1 nmol/10(7) cells per 2 h) by formation of a paramagnetic DNIC with BSA. DNIC release not only provides a route for iron loss from activated macrophages, but may also play a role in the cytotoxic and microbiostatic activity of macrophages.
Assuntos
Arginina/farmacologia , Ferro/metabolismo , Macrófagos/efeitos dos fármacos , Óxido Nítrico/metabolismo , Nitritos/metabolismo , Óxidos de Nitrogênio/metabolismo , Animais , Arginina/química , Ditiocarb , Espectroscopia de Ressonância de Spin Eletrônica , Lipopolissacarídeos , Ativação de Macrófagos , Macrófagos/química , Macrófagos/metabolismo , Camundongos , Camundongos Endogâmicos BALB CRESUMO
BACKGROUND: Chronic in vivo treatment with nitroglycerin (NTG) induces tolerance to nitrates and cross-tolerance to nitrovasodilators and endothelium-derived nitric oxide (NO). We previously identified increased vascular superoxide formation and reduced NO bioavailability as one causal mechanism. It is still controversial whether intracellular downstream signaling to nitrovasodilator-derived NO is affected as well. METHODS AND RESULTS: We therefore studied the effects of 3-day NTG treatment of rats and rabbits on activity and expression of the immediate NO target soluble guanylyl cyclase (sGC) and on the cGMP-activated protein kinase I (cGK-I). Tolerance was induced either by chronic NTG infusion via osmotic minipumps (rats) or by NTG patches (rabbits). Western blot analysis, semiquantitative reverse transcription-polymerase chain reaction, and Northern blot analysis revealed significant and comparable increases in the expression of sGC alpha(1) and beta(1) subunit protein and mRNA. Studies with the oxidative fluorescent dye hydroethidine revealed an increase in superoxide in the endothelium and smooth muscle. Stimulation with NADH increased superoxide signals in both layers. Although cGK-I expression in response to low-dose NTG was not changed, a strong reduction in vasodilator-stimulated phosphoprotein (VASP) serine239 phosphorylation (specific substrate of cGK-I) was observed in tolerant tissue from rats and rabbits. Concomitant in vivo and in vitro treatment with vitamin C improved tolerance, reduced oxidative stress, and improved P-VASP. CONCLUSIONS: We therefore conclude that increased expression of sGC in the setting of tolerance reflects a chronic inhibition rather than an induction of the sGC-cGK-I pathway and may be mediated at least in part by increased vascular superoxide.
Assuntos
Aorta/efeitos dos fármacos , Moléculas de Adesão Celular/metabolismo , Proteínas Quinases Dependentes de GMP Cíclico/metabolismo , Guanilato Ciclase/metabolismo , Nitroglicerina/farmacologia , Fosfoproteínas/metabolismo , Vasodilatadores/farmacologia , Administração Cutânea , Animais , Antioxidantes/farmacologia , Aorta/enzimologia , Ácido Ascórbico/farmacologia , GMP Cíclico/fisiologia , Tolerância a Medicamentos , Ativação Enzimática/efeitos dos fármacos , Indução Enzimática/efeitos dos fármacos , Bombas de Infusão Implantáveis , Infusões Intravenosas , Masculino , Proteínas dos Microfilamentos , Óxido Nítrico/metabolismo , Óxido Nítrico Sintase/metabolismo , Óxido Nítrico Sintase Tipo III , Nitroglicerina/administração & dosagem , Coelhos , Ratos , Ratos Wistar , Sistemas do Segundo Mensageiro , Superóxidos/metabolismo , Vasodilatadores/administração & dosagemRESUMO
OBJECTIVE/METHODS: Genetic hypertension is associated with an apparent endothelial dysfunction and impaired endothelium-dependent vasodilatation in response to increased flow and receptor-dependent agonists. However, the link between impaired vasodilatation and nitric oxide (NO) synthase expression is still unclear. In the present study, dilator responses were determined in the aorta and coronary circulation of 16 month old spontaneously hypertensive (SHR) and Wistar Kyoto rats (WKY). Changes in vascular reactivity were compared with alterations in superoxide anion production as well as endothelial NO synthase (NOS III) and soluble guanylyl cyclase expression. RESULTS: In the isolated perfused heart both the bradykinin- and sodium nitroprusside-induced vasodilator responses were attenuated in SHR compared to WKY. Western blot analysis revealed a parallel reduction in NOS III expression in coronary microvascular endothelial cells from SHR. Superoxide anion production in aortae from SHR was markedly elevated over that of aortae from WKY, and was almost completely abolished by pretreatment with superoxide dismutase. Superoxide dismutase induced similar relaxations in phenylephrine-preconstricted aortic rings from both SHR and WKY, but failed to restore the attenuated acetylcholine- and sodium nitroprusside-induced relaxations in SHR. No difference in NOS III expression was detected in the aortae from either strain whereas soluble guanylyl cyclase expression was markedly decreased in SHR. CONCLUSIONS: These results demonstrate that NOS III expression in different tissues is differentially affected by hypertension. Moreover, although an elevated superoxide anion production is apparent in the aorta, a reduced soluble guanylyl cyclase expression appears to account for the observed vasodilator dysfunction in SHR.
Assuntos
Guanilato Ciclase/metabolismo , Hipertensão/fisiopatologia , Isoenzimas/metabolismo , Óxido Nítrico Sintase/metabolismo , Superóxidos/metabolismo , Vasodilatação , Acetilcolina/farmacologia , Análise de Variância , Animais , Aorta Torácica , Bradicinina/farmacologia , Endotélio Vascular/efeitos dos fármacos , Endotélio Vascular/enzimologia , Hipertensão/metabolismo , Músculo Liso Vascular/efeitos dos fármacos , Músculo Liso Vascular/enzimologia , Nitroprussiato/farmacologia , Perfusão , Ratos , Ratos Endogâmicos SHR , Ratos Endogâmicos WKY , Superóxido Dismutase/farmacologia , Vasodilatadores/farmacologiaRESUMO
We analyzed the influence of aging and genetic hypertension on the function and expression of soluble guanylyl cyclase (sGC) in the aortas of prehypertensive and old spontaneously hypertensive rats (SHR) as well as in age-matched normotensive Wistar-Kyoto rats (WKY). The expression of heterodimeric sGC (alpha(1) and beta(1)) was assessed at the mRNA and protein level, and its function was assessed by the relaxant responses of phenylephrine-contracted endothelium-denuded aortic rings to the nitric oxide (NO) donor sodium nitroprusside. The vasodilator potency of sodium nitroprusside was significantly reduced (P<0.05) with age (3- to 6-fold increase in the EC(50) in old WKY and SHR compared with their young counterparts) as well as with hypertension (3-fold increase in old SHR compared with age-matched WKY), whereas the vasodilator potency of sodium nitroprusside did not differ between young SHR and WKY. A similar influence of aging and hypertension on NO-stimulated GC activity was revealed at the GC expression level: Whereas the beta(1) protein content was similar in young rats of both strains, old WKY exhibited 60% lower and old SHR exhibited 80% lower beta(1) subunit protein compared with young rats (P<0.05). Moreover, the abundance of alpha(1) and beta(1) mRNA (assessed by reverse transcriptase-polymerase chain reaction) was similar in young rats but was 2.5-fold (alpha(1)) and 4.3-fold (beta(1)) lower in old SHR compared with old WKY. In conclusion, our findings show that both aging and hypertension decrease sGC expression and its NO-dependent activation in aortic tissue. Downregulation of sGC may therefore contribute to arterial dysfunction in senescence and chronic hypertension.
Assuntos
Envelhecimento/metabolismo , Aorta Torácica/enzimologia , Guanilato Ciclase/metabolismo , Hipertensão/enzimologia , Envelhecimento/genética , Animais , Aorta Torácica/efeitos dos fármacos , Aorta Torácica/fisiopatologia , Sequência de Bases , Primers do DNA/genética , Expressão Gênica , Guanilato Ciclase/química , Guanilato Ciclase/genética , Hipertensão/genética , Hipertensão/fisiopatologia , Técnicas In Vitro , Masculino , Doadores de Óxido Nítrico/farmacologia , Nitroprussiato/farmacologia , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ratos , Ratos Endogâmicos SHR , Ratos Endogâmicos WKY , Solubilidade , Vasodilatação/efeitos dos fármacosRESUMO
Endogenously produced nitric oxide (NO) modulates nitrovasodilator-induced relaxation. We investigated the underlying mechanism in wild-type (WT) mice and endothelial NO synthase knockout (eNOS(-/-)) mice to determine whether a chronic lack of endothelial NO alters the soluble guanylyl cyclase (sGC) pathway. In aortic segments from eNOS(-/-) mice, the vasodilator sensitivity to sodium nitroprusside (SNP) was significantly greater than that in WT mice. There was no difference in sensitivity to the G-kinase I activator 8-para-chlorophenylthio-cGMP or to cromakalim. N(omega)-Nitro-L-arginine had no effect on the SNP-induced relaxation in eNOS(-/-) but increased the sensitivity in WT mice so it was no longer different than that of eNOS(-/-). Basal cGMP levels in aortic rings were significantly lower in eNOS(-/-) mice than in WT mice. SNP (300 nmol/L) induced a significantly greater cGMP accumulation in eNOS(-/-) mice than in WT mice. The maximal SNP-induced (10 micromol/L) increase in cGMP was similar in both strains. SNP-stimulated sGC activity was significantly greater in eNOS(-/-) mice than in WT mice. Incubation of aortic segments from WT mice with N(omega)-nitro-L-arginine increased sGC activity, an effect prevented by coincubation with SNP (10 micromol/L). The aortic expressions of the sGC alpha1 and beta1 subunits in WT and eNOS(-/-) mice were identical as determined with Western blot analysis. These data suggest that chronic exposure to endothelium-derived NO, as well as acute exposure to nitrovasodilator-derived NO, desensitizes sGC to activation by NO but does not alter sGC expression. Both the acute cessation of endothelial NO formation in WT mice and the chronic deficiency of NO in eNOS(-/-) mice restore the NO sensitivity of sGC and enhance vascular smooth muscle relaxation in response to nitrovasodilator agents.
Assuntos
Guanilato Ciclase/metabolismo , Óxido Nítrico Sintase/genética , Vasodilatação/genética , Animais , Aorta/efeitos dos fármacos , Aorta/enzimologia , Western Blotting , GMP Cíclico/metabolismo , Regulação Enzimológica da Expressão Gênica , Guanilato Ciclase/genética , Hipertensão/enzimologia , Hipertensão/genética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Óxido Nítrico/metabolismo , Óxido Nítrico Sintase/análise , Óxido Nítrico Sintase/metabolismo , Óxido Nítrico Sintase Tipo II , Óxido Nítrico Sintase Tipo III , Nitroprussiato/farmacologia , Técnicas de Cultura de Órgãos , Solubilidade , Vasodilatadores/farmacologiaRESUMO
We investigated the mechanisms by which cytokines lead to a diminished responsiveness of vascular smooth muscle to vasoconstrictors. The attenuation of noradrenaline-induced contraction by 6 to 24 h incubations with the cytokines, tumor necrosis factor and interleukin-1, in endothelium-denuded rabbit aorta was associated with an increase in intracellular cyclic GMP level. This increase was abolished by the stereoselective inhibitor of nitric oxide-synthase, NG-nitro-L-arginine and by cycloheximide. Formation of nitric oxide was detected in the cytosol of cytokine-treated native and cultured smooth muscle cells by activation of purified soluble guanylate cyclase, and depended on tetrahydrobiopterin, but not on Ca2(+)-calmodulin. The results indicate that cytokines induce a nitric oxide-synthase of the macrophage-type in vascular smooth muscle.
Assuntos
Aminoácido Oxirredutases/biossíntese , Citocinas/farmacologia , Músculo Liso Vascular/metabolismo , Óxido Nítrico/metabolismo , Animais , Aorta Torácica , Arginina/metabolismo , Biopterinas/análogos & derivados , Biopterinas/metabolismo , Células Cultivadas , GMP Cíclico/metabolismo , Indução Enzimática/efeitos dos fármacos , Técnicas In Vitro , Interferon gama/farmacologia , Interleucina-1/farmacologia , NADP/metabolismo , Óxido Nítrico Sintase , Coelhos , Fator de Necrose Tumoral alfa/farmacologiaRESUMO
We investigated whether calmodulin mediates the stimulating effect of Ca2+ on nitric oxide synthase in the cytosol of porcine aortic endothelial cells. Nitric oxide was quantified by activation of a purified soluble guanylate cyclase. The Ca2(+)-sensitivity of nitric oxide synthase was lost after anion exchange chromatography of the endothelial cytosol and could only be reconstituted by addition of calmodulin or heat-denatured endothelial cytosol. The Ca2(+)-dependent activation of nitric oxide synthase in the cytosol was inhibited by the calmodulin-binding peptides/proteins melittin, mastoparan, and calcineurin (IC50 450, 350 and 60 nM, respectively), but not by the calmodulin antagonist, calmidazolium. In contrast, Ca2(+)-calmodulin-reconstituted nitric oxide synthase was inhibited with similar potency by melittin and calmidazolium. The results suggest that the Ca2(+)-dependent activation of nitric oxide synthase in endothelial cells is mediated by calmodulin.
Assuntos
Aminoácido Oxirredutases/metabolismo , Cálcio/farmacologia , Calmodulina/farmacologia , Endotélio Vascular/metabolismo , Óxido Nítrico/metabolismo , Aminoácido Oxirredutases/isolamento & purificação , Animais , Calcineurina , Calmodulina/antagonistas & inibidores , Calmodulina/fisiologia , Proteínas de Ligação a Calmodulina/farmacologia , Células Cultivadas , Citosol/metabolismo , Ativação Enzimática , Guanilato Ciclase/metabolismo , Imidazóis/farmacologia , Peptídeos e Proteínas de Sinalização Intercelular , Cinética , Meliteno/farmacologia , Óxido Nítrico Sintase , Peptídeos , Fosfoproteínas Fosfatases/farmacologia , Suínos , Venenos de Vespas/farmacologiaRESUMO
Soluble guanylyl cyclase (sGC) is a key enzyme of the *NO/cGMP pathway. Many cardiovascular disorders are associated with reduced *NO-mediated effects, while vascular superoxide (O(2)*(-)) production is increased. Both radicals rapidly react to peroxynitrite. We investigated whether peroxynitrite affects the activity and protein expression of sGC in intact vascular preparations. Catalytic sGC activity and expression of the sGC-beta(1) subunit was measured by conversion of radiolabeled GTP and western blot, respectively, using cytosolic extracts from rat aorta that had been incubated for 4 h with *NO/O(2)*(-) systems (devoid of free *NO) generating either 0.13 microM or 7.5 microM peroxynitrite/min. Incubation of rat aorta with 0.13 microM peroxynitrite/min had no effect. In striking contrast, incubation with 7.5 microM peroxynitrite/min resulted in a shift of the concentration-response curve obtained with a *NO donor (p =.0004) and a reduction of maximal specific activity from 3579 +/- 495 to 2422 +/- 265 pmol cGMP/mg/min (p =.036). The expression of the sGC-beta(1) subunit was unchanged. Exposure of aorta to the O(2)*(-) component had no effect, while exposure to the *NO-component reduced sGC expression to 58.8 +/- 7% (p <.001) and maximal sGC activity from 4041 +/- 992 to 1429 +/- 491 pmol cGMP/mg/min (p =.031). These data suggest that continuous generation of extracellular peroxynitrite might interfere with the *NO/cGMP signaling in vascular cells.
Assuntos
Ácido Peroxinitroso/farmacologia , Receptores Citoplasmáticos e Nucleares/metabolismo , Animais , Aorta/efeitos dos fármacos , Aorta/enzimologia , Aorta/ultraestrutura , Western Blotting , Catálise , Citosol/enzimologia , Guanosina Trifosfato/metabolismo , Guanilato Ciclase , Masculino , Óxidos de Nitrogênio/metabolismo , Ácido Peroxinitroso/metabolismo , Ratos , Ratos Wistar , Guanilil Ciclase Solúvel , Superóxidos/metabolismo , Superóxidos/farmacologiaRESUMO
We studied the biological activity, stability and interaction of dinitrosyl-iron(II)-L-cysteine with vascular tissue. Dinitrosyl-iron(II)-L-cysteine was a potent activator of purified soluble guanylyl cyclase (EC50 10 nM with and 100 nM without superoxide dismutase) and relaxed noradrenaline-precontracted segments of endothelium-denuded rabbit femoral artery (EC50 10 nM superoxide dismutase). Pre-incubation (5 min; 310 K) of endothelium-denuded rabbit aortic segments with dinitrosyl-iron(II)-L-cysteine (0.036-3.6 mM) resulted in a concentration-dependent formation of a dinitrosyl-iron(II) complex with protein thiol groups, as detected by ESR spectroscopy. While the complex with proteins was stable for 2 h at 310 K, dinitrosyl-iron(II)-L-cysteine in aqueous solution (36-360 microM) decomposed completely within 15 min, as indicated by disappearance of its isotropic ESR signal at gav = 2.03 (293 K). Aortic segments pre-incubated with dinitrosyl-iron(II)-L-cysteine released a labile vasodilating and guanylyl cyclase activating factor. Perfusion of these segments with N-acetyl-L-cysteine resulted in the generation of a low molecular weight dinitrosyl-iron(II)-dithiolate from the dinitrosyl-iron(II) complex with proteins, as revealed by the shape change of the ESR signal at 293 K. The low molecular weight dinitrosyl-iron(II)-dithiolate accounted for an enhanced guanylyl cyclase activation and vasodilation induced by the aortic effluent. We conclude that nitric oxide (NO) produced by, or acting on vascular cells can be stabilized and stored as a dinitrosyl-iron(II) complex with protein thiols, and can be released from cells in the form of a low molecular weight dinitrosyl-iron(II)-dithiolate by intra- and extracellular thiols.
Assuntos
Vasos Sanguíneos/metabolismo , Cisteína/análogos & derivados , Guanilato Ciclase/metabolismo , Óxido Nítrico/farmacologia , Óxidos de Nitrogênio/farmacologia , Proteínas/metabolismo , Compostos de Sulfidrila/farmacologia , Vasodilatação/efeitos dos fármacos , Animais , Aorta/metabolismo , Vasos Sanguíneos/efeitos dos fármacos , Cisteína/farmacologia , Espectroscopia de Ressonância de Spin Eletrônica , Ativação Enzimática/efeitos dos fármacos , Artéria Femoral/metabolismo , Ligação Proteica , CoelhosRESUMO
We investigated whether sodium diethyldithiocarbamate (DETC), an inhibitor of the nuclear transcription factor kappa B (NFkappa B), modulates induction of NO synthase (NOS) in murine bone marrow-derived macrophages. A short exposure (between 1 and 16 h) of L929-cell medium-preconditioned macrophages to E. coli lipopolysaccharide (LPS) significantly increased the level of NOS mRNA, and elicited NO formation as detected by electron spin resonance spectroscopy and by the release of nitrite. DETC (0.1-1 mM) present during stimulation with LPS prevented the increase in NOS mRNA and the expression of NOS activity. These findings suggest that NFkappa B is involved in the signal transduction pathway linking stimulation of macrophages by LPS with transcription of the gene encoding inducible NOS.
Assuntos
Aminoácido Oxirredutases/biossíntese , Ditiocarb/farmacologia , Macrófagos/enzimologia , Aminoácido Oxirredutases/genética , Animais , Northern Blotting , Medula Óssea/efeitos dos fármacos , Medula Óssea/enzimologia , Células da Medula Óssea , Células Cultivadas , Meios de Cultivo Condicionados , Sondas de DNA , Indução Enzimática/efeitos dos fármacos , Células L , Macrófagos/citologia , Macrófagos/efeitos dos fármacos , Camundongos , Camundongos Endogâmicos BALB C , NF-kappa B/antagonistas & inibidores , Óxido Nítrico Sintase , Nitritos/metabolismo , RNA Mensageiro/análise , RNA Mensageiro/metabolismoRESUMO
The nitrogen monoxide radical (NO*) forms paramagnetic mono- and dinitrosyl-iron complexes in biologic tissues. To establish a noninvasive technique for in vivo NO* imaging, we evaluated the suitability of these complexes as magnetic resonance (MR) contrast agents, making use of the ability of the unpaired electrons of the complexes to enter into dynamic nuclear polarization with water protons and hence produce enhancement on images generated by the technique of proton-electron-double-resonance imaging (PEDRI). Phantom solutions of synthetic nitrosyl-iron complexes (NICs) altered the signal intensity of PEDRI images. The dinitrosyl-iron complex (DNIC) with serum albumin induced a significantly larger signal alteration than the mononitrosyl-iron complex (MNIC) with dithiocarbamate. Exposure of rat liver to sodium nitroprusside (SNP) by ex vivo and in situ perfusion induced a composite X-band electron spin resonance (ESR) spectrum of the isolated liver characteristic of a MNIC and DNIC. On storage of the tissue, the MNIC signal disappeared and the DNIC signal intensity increased. Correspondingly, in cross-sectional PEDRI images taken at room temperature, the SNP-exposed livers initially exhibited a weak signal that strongly increased with time. In conclusion, NICs can be detected using PEDRI and could be exploited for in vivo NO* imaging.
Assuntos
Ferro/análise , Imageamento por Ressonância Magnética/métodos , Óxidos de Nitrogênio/análise , Animais , Meios de Contraste/química , Cisteína/análogos & derivados , Cisteína/química , Espectroscopia de Ressonância de Spin Eletrônica , Fígado/química , Masculino , Nitroprussiato/química , Ratos , Ratos Sprague-Dawley , Albumina Sérica/química , Temperatura , Fatores de TempoRESUMO
The primary structure of the 70 kDa subunit of soluble bovine guanylate cyclase, which catalyzes the formation of cyclic GMP from GTP, has been determined. The alignment of six different clones out of two bovine libraries yielded a total of 3.1 kb with a coding region of 1857 bases. The open reading frame encodes a protein of 619 amino acids and a molecular mass of 70.5 kDa. Antibodies raised against a synthetic peptide, which corresponded to the C-terminus of the deduced sequence precipitated guanylate cyclase activity from guanylate cyclase-enriched preparations.
Assuntos
Guanilato Ciclase/genética , Sequência de Aminoácidos , Animais , Sequência de Bases , Bovinos , Clonagem Molecular , DNA/genética , Pulmão/enzimologia , Substâncias Macromoleculares , Dados de Sequência Molecular , Peso MolecularRESUMO
1. The effects of extracellular Ca2+ on the release of endothelium-derived relaxing factor (EDRF) and prostacyclin (PGI2), and on the intracellular free calcium concentration [( Ca2+]i), were studied in cultured bovine aortic endothelial cells. 2. Receptor-mediated stimulation of endothelial cells with bradykinin (10 nM) elicited a transient release of EDRF (assayed by its stimulant effect on purified soluble guanylate cyclase) and of PGI2 (measured by radioimmunoassay for 6-keto prostaglandin F1 alpha). 3. Bradykinin (10 nM) also increased [Ca2+]i (measured with the fluorescent probe indo-1) from 125 +/- 11 nM to 631 +/- 59 nM, with the same time course as for autacoid release. 4. In Ca2+-free medium, [Ca2+]i was still increased by bradykinin but declined faster (within 1 min) to resting levels than in the presence of extracellular Ca2+. 5. PGI2 release was almost completely abolished in Ca2+-free medium. The intracellular calcium antagonist TMB-8 evoked a similar inhibition of PGI2 release. 6. In contrast, bradykinin-induced EDRF release was not significantly affected by TMB-8 but was completely abolished in Ca2+-free medium. 7. When endothelial cells were stimulated with the receptor-independent drug thimerosal (an inhibitor of the enzyme acyl-CoA-lysolecithin-acyl-transferase; 5 microM), a long-lasting release of EDRF (greater than 90 min) and PGI2 (greater than 20 min) was observed. 8. In contrast to bradykinin stimulation, thimerosal-induced autacoid release was associated with only a slight increase of [Ca2+]i to 201 +/- 13 nM after 40 min. 9. After removal of extracellular Ca2 + from thimerosal-stimulated endothelial cells, [Ca2+] was little affected during the observation time of 90s. EDRF release was completely abolished within 90s whereas PGI2 release was unchanged. 10. We conclude that EDRF production is directly controlled by extracellular Ca2+ during both receptor-dependent and independent stimulation. This effect of extracellular Ca2 + is not mediated by changes in [Ca2+]i. In contrast, PGI2 release is closely correlated to [Ca2+]i in bradykininstimulated endothelial cells. However, the results obtained during thimerosal stimulation indicate that there is not necessarily a tight coupling between the absolute level of [Ca2+]i and the amount of PGI2 released. 9. After removal of extracellular Ca2 + from thimerosal-stimulated endothelial cells, [Ca2+] was little affected during the observation time of 90s. EDRF release was completely abolished within 90s whereas PGI2 release was unchanged. 10. We conclude that EDRF production is directly controlled by extracellular Ca2+ during both receptor-dependent and independent stimulation. This effect of extracellular Ca2 + is not mediated by changes in [Ca2+]i. In contrast, PGI2 release is closely correlated to [Ca2+]i in bradykininstimulated endothelial cells. However, the results obtained during thimerosal stimulation indicate that there is not necessarily a tight coupling between the absolute level of [Ca2+]i and the amount of PGI2 released. 9. After removal of extracellular Ca2 + from thimerosal-stimulated endothelial cells, [Ca2+] was little affected during the observation time of 90s. EDRF release was completely abolished within 90s whereas PGI2 release was unchanged. 10. We conclude that EDRF production is directly controlled by extracellular Ca2+ during both receptor-dependent and independent stimulation. This effect of extracellular Ca2 + is not mediated by changes in [Ca2+]i. In contrast, PGI2 release is closely correlated to [Ca2+]i in bradykininstimulated endothelial cells. However, the results obtained during thimerosal stimulation indicate that there is not necessarily a tight coupling between the absolute level of [Ca2+]i and the amount of PGI2 released.
Assuntos
Fatores Biológicos/metabolismo , Cálcio/fisiologia , Epoprostenol/metabolismo , Animais , Bradicinina/farmacologia , Bovinos , Células Cultivadas , Endotélio Vascular/citologia , Endotélio Vascular/metabolismo , Óxido Nítrico , Timerosal/farmacologia , Fatores de TempoRESUMO
1. In the present study we examined whether interleukin-1 beta (IL-1 beta) increases the activity of adenylyl cyclase in vascular smooth muscle cells and determined its role in the cytokine-induced expression of the inducible nitric oxide synthase (iNOS) and activation of nuclear transcription factor-kappa B (NF-kappa B). In addition the interaction between cyclic AMP- and cyclic GMP-elevating agonists on the IL-1 beta-stimulated expression of iNOS was examined. 2. Exposure of vascular smooth muscle cells to IL-1 beta stimulated the formation of cyclic AMP but not of cyclic GMP. The intracellular level of cyclic AMP reached a maximum within 1 h and then gradually declined over the next 5 h. This IL-1 beta (60 u ml-1)-stimulated formation of cyclic AMP was modest (about 3 fold at 60 u ml-1 for 1 h) compared to that evoked by isoprenaline (about 9 fold at 3 x 10(-6) M for 2 min). 3. The IL-1 beta (60 u ml-1 for 24 h)-stimulated accumulation of nitrite, which was taken as an index of NO production, was concentration-dependently increased by preferential inhibitors of cyclic AMP-dependent phosphodiesterases (rolipram and trequinsin). This effect was reproduced by a specific activator of the cyclic AMP-dependent protein kinase(s) A, Sp-8-CPT-cAMPS (10(-4) M) but was prevented by a specific inhibitor of cyclic AMP-dependent protein kinase(s) A, Rp-8-CPT-cAMPS (10(-4) M). These compounds alone [rolipram (10(-6) M), trequinsin (3 x 10(-6) M) and Sp-8-CPT-cAMPS (10(-4) M)] slightly but significantly increased the release of nitric oxide while Rp-8-CPT-cAMPS elicited no such effect. 4. Inducible NOS protein was expressed in IL-1 beta (30 u ml-1, 24 h)-stimulated smooth muscle cells as assessed by Western blot analysis. The level of iNOS protein was markedly increased in smooth muscle cells which had been exposed to IL-1 beta in combination with either rolipram (3 x 10(-6) M) or Sp-8-CPT-cAMPS (10(-4) M) but was reduced in those exposed to IL-1 beta and Rp-8-CPT-cAMPS (10(-4) M). A weak expression of iNOS protein was found in smooth muscle cells which had been exposed to either Sp-8-CPT-cAMPS or rolipram alone for 24 h while Rp-8-CPT-cAMPS elicited no such effect. 5. Exposure of smooth muscle cells to IL-1 beta (30 u ml-1) for 30 min increased the level of NF-kappa B-DNA complexes in nuclear extracts as detected by electrophoretic mobility shift assay. Similar levels of NF-kappa B-DNA complexes were found in cells which had been exposed to IL-1 beta in combination with either Sp-8-CPT-cAMPS (10(-4) M), trequinsin (10(-6) M) or rolipram (10(-6) M). None of the modulators alone affected the basal level of NF-kappa B binding activity. 6. NO-donors [sodium nitroprusside (SNP) 10(-4) M; dinitrosyl-iron-di-L-cysteine-complex (DNIC), 10(-4) M; 3-morpholino-sydnonimine (SIN-1), 10(-4) M] and atrial natriuretic factor (10(-6) M) significantly increased the IL-1 beta (30 or 60 u ml-1, 24 h)-stimulated expression of iNOS protein and activity as assessed indirectly by the conversion of oxyhaemoglobin to methaemoglobin. In the absence of IL-1 beta, SNP (10(-4) M, 24 h) but not the other cyclic GMP-dependent vasodilators caused a modest expression of iNOS protein. No such effect was found in smooth muscle cells exposed to SNP in combination with Rp-8-CPT-cAMPS (10(-4) M) while an increased level of iNOS protein was found in those exposed to SNP in combination with either Sp-8-CPT-cAMPS (10(-4) M) or rolipram (3 x 10(-6) M). 7. Exposure of vascular smooth muscle cells to either S-nitroso-L-cysteine (Cys-SNO, 10(-4) M), SNP (10(-4) M) or SIN-1 (10(-4) M) for 35 min affected minimally the basal activation of NF-kappa B but abolished that evoked by IL-1 beta (30 u ml-1 added during the last 30 min). However, addition of Cys-SNO following the stimulation with IL-1 beta (during the last 5 min of the 30 min exposure period) reduced the level of NF-kappa B-DNA complexes only slightly. 8. These data indicate that the cyclic AMP-dependent pathway plays a decisi
Assuntos
AMP Cíclico/fisiologia , GMP Cíclico/metabolismo , Músculo Liso Vascular/efeitos dos fármacos , Óxido Nítrico Sintase/biossíntese , Vasodilatadores/farmacologia , Animais , Interleucina-1/farmacologia , Masculino , Músculo Liso Vascular/citologia , Músculo Liso Vascular/enzimologia , NF-kappa B/metabolismo , Óxido Nítrico Sintase/metabolismo , Nitritos/metabolismo , Ratos , Ratos Endogâmicos WKYRESUMO
1. In the present study we assessed the formation of nitric oxide (NO) from classical and thiol-containing organic nitrates in vascular tissues and organs of anaesthetized rabbits, and established a relationship between the relaxant response elicited by nitroglycerin (NTG) and NO formation in the rabbit isolated aorta. Furthermore, the effect of isolated cytochrome P450 on NO formation from organic nitrates was investigated. 2. Rabbits received diethyldithiocarbamate (DETC; 200 mg kg-1 initial bolus i.p. and 200 mg kg-1 during 20 min, i.v.) and either saline, or one of the following organic nitrates: nitroglycerin (NTG, 0.5 mg kg-1), isosorbide dinitrate (ISDN), N-(3-nitratopivaloyl)-L-cysteine ethylester (SPM 3672), S-carboxyethyl-N-(3-nitratopivaloyl)-L-cysteine ethylester (SPM 5185), at 10 mg kg-1 each. After 20 min the animals were killed, blood vessels and organs were removed, and subsequently analyzed for spin-trapped NO by cryogenic electron spin resonance (e.s.r.) spectroscopy. 3. In the saline-treated control group, NO remained below the detection limit in all vessels and organs. In contrast, all of the nitrates tested elicited measurable NO formation, which was higher in organs (liver, kidney, heart, lung, spleen) (up to 4.8 nmol g-1 20 min-1) than in blood vessels (vena cava, mesenteric bed, femoral artery, aorta) (up to 0.7 nmol g-1 20 min-1). Classical organic nitrates (NTG, ISDN) formed NO preferentially in the mesenteric bed and the vena cava, while the SPM compounds elicited comparable NO formation in veins and arteries. 4. Using a similar spin trapping technique, NO formation was assessed in vitro in phenylephrine-precontracted rabbit aortic rings. The maximal relaxation elicited by a first exposure (10 min) to NTG (0.3 to 10 microM) was positively correlated (r = 0.8) with the net increase (NTG minus basal) of NO spin-trapped during a second exposure to the same concentration of NTG in the presence of DETC. 5. Cytochrome P450 purified from rabbit liver enhanced NO formation in a NADPH-dependent fashion from NTG, but not from the other nitrates, as assessed by activation of purified soluble guanylyl cyclase. 6. We conclude that the vessel selective action of different organic nitrates in vivo reflects differences in vascular NO formation. Thus, efficient preload reduction by classical organic nitrates can be accounted for by higher NO formation in venous capacitance as compared to arterial conductance and resistance vessels. In contrast, NO is released from cysteine-containing nitrates (SPMs) to a similar extent in arteries and veins, presumably independently of an organic nitrate-specific biotransformation. Limited tissue bioavailability of NTG and ISDN might account for low NO formation in the aorta, while true differences in biotransformation seem to account for differences in NO formation in the other vascular tissues.
Assuntos
Vasos Sanguíneos/metabolismo , Nitratos/metabolismo , Óxido Nítrico/biossíntese , Animais , Aorta/efeitos dos fármacos , Aorta/metabolismo , Cisteína/análogos & derivados , Cisteína/farmacologia , Sistema Enzimático do Citocromo P-450/metabolismo , Dipeptídeos/farmacologia , Espectroscopia de Ressonância de Spin Eletrônica , Guanilato Ciclase/metabolismo , Técnicas In Vitro , Contração Isométrica/efeitos dos fármacos , Dinitrato de Isossorbida/farmacologia , Rim/metabolismo , Fígado/metabolismo , Relaxamento Muscular/efeitos dos fármacos , Relaxamento Muscular/fisiologia , Nitratos/farmacologia , Nitroglicerina/farmacologia , Coelhos , Sensibilidade e Especificidade , Solubilidade , Compostos de Sulfidrila/metabolismo , Vasodilatadores/farmacologia , Veias Cavas/metabolismoRESUMO
1. Acetylcholine, ionophore A23187 and melittin induced endothelium-dependent relaxations of preconstricted strips of rabbit aorta. These relaxations are likely to be mediated by endothelium-derived relaxing factor (EDRF). 2. Relaxations in response to acetylcholine (1 microM) were inhibited by the following lipoxygenase inhibitors, with the approximate IC50 values indicated in parentheses: gossypol (1.5 microM), nordihydroguairetic acid (NDGA, 5 microM), AA 861 (20 microM), phenidone (30 microM), quercetin (40 microM), BW 755C (300 microM), and piriprost (500 microM); with cirsiliol 50% inhibition was not achieved. Acetylcholine-induced relaxations were also blocked by the cytochrome P-450-mono-oxygenase inhibitors proadifen (SKF 525A, 4 microM), metyrapone (300 microM), and cimetidine (300 microM); 7,8 benzoflavone had no effect up to 100 microM. 3. The more potent inhibitors were also tested against relaxations induced by A23187 (0.1 microM) and melittin (1 microM) and produced partial inhibition of these relaxations. 4. The mechanism of action of the more potent inhibitors was investigated in a bioassay system. EDRF was produced in columns filled with cultured human endothelial cells. The factor was bioassayed with endothelium denuded segments of rabbit femoral artery. When added to effluent of the column, NDGA, AA861, proadifen and metyrapone inhibited the EDRF-induced vasodilatation, whereas gossypol had no effect. Gossypol, however, blocked EDRF production when infused through the column. 5. The more potent inhibitors were also tested to determine their effect on purified soluble guanylate cyclase. While gossypol, NDGA and proadifen had no appreciable effects, basal and nitroprusside (50 microM)-stimulated guanylate cyclase activity was inhibited by AA861 and metyrapone. 6. These data suggest that many of the above compounds inhibit EDRF by mechanisms other than lipoxygenase- or cytochrome P-450-mono-oxygenase inhibition.
Assuntos
Venenos de Abelha/farmacologia , Produtos Biológicos/antagonistas & inibidores , Calcimicina/farmacologia , Inibidores Enzimáticos/farmacologia , Inibidores de Lipoxigenase , Meliteno/farmacologia , Oxigenases/antagonistas & inibidores , Acetilcolina/farmacologia , Animais , Aorta/efeitos dos fármacos , Células Cultivadas , Sistema Enzimático do Citocromo P-450 , Guanilato Ciclase/metabolismo , Humanos , Óxido Nítrico , CoelhosRESUMO
1. We studied the effects of 3-(5'-hydroxymethyl-2'furyl)-1-benzyl indazole (YC-1) on the activity of purified soluble guanylyl cyclase (sGC), the formation of guanosine-3':5' cyclic monophosphate (cyclic GMP) in vascular smooth muscle cells (VSMC), and on the tone of rabbit isolated aortic rings preconstricted by phenylephrine (PE). In addition, we assessed the combined effect of YC-1, and either NO donors, or superoxide anions on these parameters. 2. YC-1 elicited a direct concentration-dependent activation of sGC (EC50 18.6 +/- 2.0 microM), which was rapid in onset and quickly reversible upon dilution. YC-1 altered the enzyme kinetics with respect to GTP by decreasing KM and increasing Vmax. Activation of sGC by a combination of sodium nitroprusside (SNP) and YC-1 was superadditive at low and less than additive at high concentrations, indicating a synergistic activation of the enzyme by both agents. A specific inhibitor of sGC, 1H-(1,2,4)-oxdiazolo-(4,3-a)-6-bromo-quinoxazin-1-one (NS 2028), abolished activation of the enzyme by either compound. 3. YC-1 induced a concentration-dependent increase in intracellular cyclic GMP levels in rat cultured aortic VSMC, which was completely inhibited by NS 2028. YC-1 applied at the same concentration as SNP elicited 2.5 fold higher cyclic GMP formation. Cyclic GMP-increases in response to SNP and YC-1 were additive. 4. YC-1 relaxed preconstricted endothelium-denuded rabbit aortic rings in a concentration-dependent manner (50% at 20 microM) and markedly increased cyclic GMP levels. Relaxations were inhibited by NS 2028. A concentration of YC-1 (3 microM), which elicited only minor effects on relaxation and cyclic GMP, increased the vasodilator potency of SNP and nitroglycerin (NTG) by 10 fold and markedly enhanced SNP- and NTG-induced cyclic GMP formation. 5. Basal and YC-1-stimulated sGC activity was sensitive to inhibition by superoxide (O-2) generated by xanthine/xanthine oxidase, and was protected from this inhibition by superoxide dismutase (SOD). YC-1-stimulated sGC was also sensitive to inhibition by endogenously generated (O-2 in rat preconstricted endothelium-denuded aortic rings. Relaxation to YC-1 was significantly attenuated in aortae from spontaneously hypertensive rats (SHR), which generated O-2 at a higher rate than aortae from normotensive Wistar Kyoto rats (WKY). SOD restored the vasodilator responsiveness of SHR rings to YC-1. 6. In conclusion, these results indicate that YC-1 is an NO-independent, O-2-sensitive, direct activator of sGC in VSMC and exerts vasorelaxation by increasing intracellular cyclic GMP levels. The additive or even synergistic responses to NO-donors and YC-1 in cultured VSMC and isolated aortic rings apparently reflect the direct synergistic action of YC-1 and NO on the sGC. The synergism revealed in this in vitro study suggests that low doses of YC-1 may be of therapeutic value by permitting the reduction of nitrovasodilator dosage.
Assuntos
GMP Cíclico/biossíntese , Guanilato Ciclase/metabolismo , Indazóis/farmacologia , Músculo Liso Vascular/efeitos dos fármacos , Vasodilatadores/farmacologia , Animais , Células Cultivadas , Ativação Enzimática/efeitos dos fármacos , Técnicas In Vitro , Masculino , Relaxamento Muscular/efeitos dos fármacos , Óxido Nítrico/análise , Coelhos , Ratos , Ratos Endogâmicos WKY , Superóxidos/farmacologiaRESUMO
We assessed whether pharmacological inhibition of CuZn-superoxide dismutase (SOD) mimics the molecular mechanism of either in vitro or in vivo nitrovasodilator tolerance. In endothelium-intact aortic rings from in vivo tolerant rabbits the GTN- and acetylcholine (ACh)-induced maximal relaxation was attenuated by 36 and 23%, respectively. In vitro treatment of control rings with GTN (1 h 10 microM) similarly attenuated the vasorelaxant response to GTN, but not to ACh. Formation of superoxide radicals (*O2-) in endothelium-intact rings (lucigenin-chemiluminescence) increased 2.5 fold in in vivo tolerance, but significantly decreased in in vitro tolerance. The membrane associated NADH oxidase activity was increased 2.5 fold in homogenates of in vivo tolerant aortae, but was not changed in in vitro tolerant aorta. Conversely, SOD activity and protein expression was halved in in vivo tolerance, but SOD activity was not altered by in vitro tolerance. The *O2- scavenger tiron (10 mM) effectively restored the vasorelaxant response to GTN in in vivo tolerant aortic rings, but not the reduced response to GTN in in vitro tolerant rings. Pretreatment (1 h) of vessels with diethyldithiocarbamate (DETC; 10 mM) attenuated vasorelaxant responses to GTN and ACh, increased vascular *O2- production, and inhibited SOD activity in vessel homogenates to a similar degree as observed in in vivo tolerance. DETC-treatment of in vivo-tolerant vessels induced an additional increase in *O2- production. Increased *O2- production in in vivo nitrate tolerant aorta is associated with activation of vascular NADH oxidase and inactivation of CuZnSOD. Therefore, in vivo tolerance can be mimicked by in vitro inhibition of CuZnSOD, but not by in vitro exposure to GTN, which does not affect vascular *O2- production, NADH oxidase and CuZnSOD.
Assuntos
Nitroglicerina/farmacologia , Superóxido Dismutase/fisiologia , Sal Dissódico do Ácido 1,2-Di-Hidroxibenzeno-3,5 Dissulfônico/farmacologia , Acetilcolina/farmacologia , Animais , Vasos Sanguíneos/enzimologia , Ditiocarb/farmacologia , Tolerância a Medicamentos , Feminino , Masculino , Complexos Multienzimáticos/metabolismo , NADH NADPH Oxirredutases/metabolismo , Coelhos , Superóxido Dismutase/antagonistas & inibidores , Superóxidos/metabolismo , Vasodilatação/efeitos dos fármacosRESUMO
1 The haeme-containing soluble guanylyl cyclase (alpha1beta1-heterodimer) is a major intracellular receptor and effector for nitric oxide (NO) and carbon monoxide (CO) and mediates many of their biological actions by increasing cyclic GMP. We have synthesized new oxadiazolo-benz-oxazins and have assessed their inhibitory actions on guanylyl cyclase activity in vitro, on the formation of cyclic GMP in cultured cells and on the NO-dependent relaxation of vascular and non-vascular smooth muscle. 2 Soluble guanylyl cyclase, purified to homogeneity from bovine lung, was inhibited by 4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one (NS 2028) in a concentration-dependent and irreversible manner (IC50 30 nM for basal and 200 nM for NO-stimulated enzyme activity). Evaluation of the inhibition kinetics according to Kitz & Wilson yielded a value of 8 nM for Ki, the equilibrium constant describing the initial reversible reaction between inhibitor and enzyme, and 0.2 min(-1) for the rate constant k3 of the subsequent irreversible inhibition. Inhibition was accompanied by a shift in the soret absorption maximum of the enzyme's haem cofactor from 430 to 390 nm. 3 S-nitroso-glutathione-enhanced soluble guanylyl cyclase activity in homogenates of mouse cerebellum was inhibited by NS 2028 (IC50 17 nM) and by 17 structural analogues in a similar manner, albeit with different potency, depending on the type of substitution at positions 1, 7 and 8 of the benzoxazin structure. Small electronegative ligands such as Br and Cl at position 7 or 8 increased and substitution of the oxygen at position 1 by -S-,- NH- or -CH2- decreased the inhibition. 4 In tissue slices prepared from mouse cerebellum, neuronal NO synthase-dependent activation of soluble guanylyl cyclase by the glutamate receptor agonist N-methyl-D-aspartate was inhibited by NS 2028 (IC50 20 nM) and by two of its analogues. Similarly, 3-morpholino-sydnonimine (SIN-1)-elicited formation of cyclic GMP in human cultured umbilical vein endothelial cells was inhibited by NS 2028 (IC50 30 nM). 5 In prostaglandin F2alpha-constricted, endothelium-intact porcine coronary arteries NS 2028 elicited a concentration-dependent increase (65%) in contractile tone (EC50 170 nM), which was abolished by removal of the endothelium. NS 2028 (1 microM) suppressed the relaxant response to nitroglycerin from 88.3+/-2.1 to 26.8+/-6.4% and induced a 9 fold rightward shift (EC50 15 microM) of the concentration-relaxation response curve to nitroglycerin. It abolished the relaxation to sodium nitroprusside (1 microM), but did not affect the vasorelaxation to the KATP channel opener cromakalim. Approximately 50% of the relaxant response to sodium nitroprusside was recovered after 2 h washout of NS 2028. 6 In phenylephrine-preconstricted, endothelium-denuded aorta of the rabbit NS 2028 (1 microM) did not affect relaxant responses to atrial natriuretic factor, an activator of particulate guanylyl cyclase, or forskolin, an activator of adenylyl cyclase. 7 NO-dependent relaxant responses in non-vascular smooth muscle were also inhibited by NS 2028. The nitroglycerin-induced relaxation of guinea-pig trachea preconstricted by histamine was fully inhibited by NS 2028 (1 microM), whereas the relaxations to terbutaline, theophylline and vasoactive intestinal polypeptide (VIP) were not affected. The relaxant responses to electrical field stimulation of non-adrenergic, non-cholinergic nerves in the same tissue were attenuated by 50% in the presence of NS 2028 (1 microM). 8 NS 2028 and its analogues, one of which is the previously characterized 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), appear to be potent and specific inhibitors of soluble guanylyl cyclase present in various cell types. Oxidation and/or a change in the coordination of the haeme-iron of guanylyl cyclase is a likely inhibitory mechanism.
Assuntos
Inibidores Enzimáticos/farmacologia , Guanilato Ciclase/antagonistas & inibidores , Oxidiazóis/farmacologia , Oxazinas/farmacologia , Animais , Bovinos , Células Cultivadas , Cerebelo/efeitos dos fármacos , Cerebelo/metabolismo , GMP Cíclico/biossíntese , Endotélio Vascular/metabolismo , Guanilato Ciclase/metabolismo , Cobaias , Heme/análise , Humanos , Técnicas In Vitro , Cinética , Masculino , Camundongos , Contração Muscular/efeitos dos fármacos , Músculo Liso Vascular/efeitos dos fármacos , Músculo Liso Vascular/metabolismo , Coelhos , Solubilidade , Espectrofotometria , Relação Estrutura-Atividade , Suínos , Veias Umbilicais/metabolismoRESUMO
Human glutathione reductase (GR) and rat liver glutathione-S-transferases (GSTs) had been shown to be inhibited by the nitric oxide (NO) carrier S-nitroso-glutathione (GSNO). We have now extended these studies by measuring the effects of dinitrosyl-iron complexed thiols (DNIC-[RSH]2) on human GR, GST and glutathione peroxidase. DNIC-[RSH]2 represent important transport forms of NO but also of iron ions and glutathione in vivo. Human GR was found to be inhibited by dinitrosyl-iron-di-glutathione (DNIC-[GSH]2) and dinitrosyl-iron-di-L-cysteine (DNIC-Cys2) in two ways: both compounds were competitive with glutathione disulfide (GSSG), the inhibition constant (Ki) for reversible competition of DNIC-[GSH]2 with GSSG being approximately 5 microM; preincubating GR for 10 min with 4 microM DNIC-[GSH]2 and 40 microM DNIC-Cys2, respectively, led to 50% irreversible enzyme inactivation. More than 95% GR inactivation was achieved by incubation with 36 microM DNIC-[GSH]2 for 30 min. This inhibition depended on the presence of NADPH. Absorption spectra of inhibited GR showed that the charge-transfer interaction between the isoalloxazine moiety of the prosthetic group flavin adenine dinucleotide (FAD) and the active site thiol Cys63 is disturbed by the modification. Cys2 and FAD could be ruled out as sites of the modification. Isolated human placenta glutathione-S-transferase and GST activity measured in hemolysates were also inhibited by DNIC-[GSH]2. This inhibition, however, was reversible and competitive with reduced glutathione, the Ki being 20 nM. The inhibition of GST induced by GSNO was competitive with reduced glutathione (GSH) (Ki = 180 microM) and with the second substrate of the reaction, 1-chloro-2,4,-dinitrobenzene (Ki = 170 microM). An inhibition of human glutathione peroxidase by GSNO or DNIC-[RSH]2 was not detectable. Inactivation of GR by DNIC-[GSH]2 is by two orders of magnitude more effective than modification by GSNO; this result and the very efficient inhibition of GST point to a role of DNIC-[RSH]2 in glutathione metabolism.