Diverse effects of taurine on vascular response and inflammation in GSH depletion model in rabbits

OBJECTIVE

A reduction in GSH and an increase in free radicals are observed in inflammatory diseases, indicating oxidative stress. Taurine protects cells from the cytotoxic effects of inflammation. There have been limited studies to date evaluating the effect of taurine in oxidative stress-induced vascular dysfunction and its role in vascular inflammatory diseases. Therefore, we aimed to investigate the effect of taurine on the regulation of vascular tonus and vascular inflammatory markers in rabbit aortae and carotid arteries in oxidative stress-induced by GSH depletion.

MATERIALS AND METHODS

Rabbits were treated subcutaneously with buthionine sulfoximine (BSO), GSH-depleting compound and/or taurine. Cumulative concentration-response curves for acetylcholine (ACh), phenylephrine and 5-hydroxytriptamine (5-HT) were constructed with or without Nω-nitro-L-arginine (LNA) in the carotid artery and aorta rings. Immunohistochemical staining was performed for TNF-α and IL-1β.

RESULTS

BSO increased ACh-induced NO-dependent relaxations, phenylephrine-induced contractions in the carotid artery and 5-HT induced-contractions in both the carotid artery and the aorta. BSO decreased EDHF dependent relaxations only in the aorta. ACh-induced NO-dependent relaxations and augmented contractions were normalized by taurine. BSO increased TNF-α expressions in both carotid arteries and aortas, which were reversed by taurine. The BSO-induced increase in IL-1β was reversed by taurine only in aortae.

CONCLUSIONS

Treatment with BSO resulted in vascular reactivity changes and increased immunostaining of TNF-α in mainly carotid arteries in this model of oxidative stress. The effect of taurine on BSO-induced vascular reactivity changes varied depending on the vessel. The inhibition of the increase in TNF-α expression by taurine in both carotid arteries and aortae supports the proposal that taurine has a beneficial effect in the treatment of inflammatory diseases such as atherosclerosis.

GTP cyclohydrolase I/BH4 pathway protects EPCs via suppressing oxidative stress and thrombospondin-1 in salt-sensitive hypertension

Endothelial progenitor cells (EPCs) are both reduced and dysfunctional in hypertension that correlates inversely with its mortality, but the mechanisms are poorly understood. Endothelial nitric oxide synthase (eNOS) critically regulates EPC mobilization and function but is uncoupled in salt-sensitive hypertension because of the reduced cofactor tetrahydrobiopterin (BH4). We tested the hypothesis that GTP cyclohydrolase I (GTPCH I), the rate-limiting enzyme of BH4 de novo synthesis, protects EPCs and its function in deoxycorticosterone acetate (DOCA)-salt mice. EPCs were isolated from peripheral blood and bone marrow of wild-type (WT), WT DOCA-salt, endothelial-specific GTPCH transgenic (Tg-GCH), GTPCH transgenic DOCA-salt, and BH4-deficient hph-1 mice. In WT DOCA-salt and hph-1 mice, EPCs were significantly decreased with impaired angiogenesis and adhesion, which were restored in Tg-GCH DOCA-salt mice. Superoxide (O₂⁻) and nitric oxide (NO) levels in EPCs were elevated and reduced, respectively, in WT DOCA-salt and hph-1 mice; both were rescued in Tg-GCH DOCA-salt mice. eNOS(-/-)/GCH(+/-) hybrid mice demonstrated that GTPCH preserved the circulating EPC number, reduced intracellular O₂⁻ in EPCs, and ameliorated EPC dysfunction independent of eNOS in DOCA-salt hypertension. Secreted thrombospondin-1 (TSP-1; a potent angiogenesis inhibitor) from EPCs was elevated in WT DOCA-salt and hph-1 but not DOCA-salt Tg-GCH mice. In vitro treatment with BH4, polyethylene glycol-superoxide dismutase (PEG-SOD), or Nomega-nitro-L-arginine (L-NNA) significantly augmented NO and reduced TSP-1 and O₂⁻ levels from EPCs of WT DOCA-salt mice. These results demonstrated, for the first time, that the GTPCH/BH4 pathway critically regulates EPC number and function in DOCA-salt hypertensive mice, at least in part, via suppressing TSP-1 expression and oxidative stress.

Inhibitory effects of benzoate on chiral inversion and clearance of N(G)-nitro-arginine in conscious rats

N(G)-nitro-arginine (NNA) is known to exhibit stereoselective pharmacokinetics in which N(G)-nitro-d-arginine (d-NNA) has a faster clearance rate than N(G)-nitro-l-arginine (l-NNA) in anesthetized rats, and d-NNA undergoes unidirectional chiral inversion. It was postulated that chiral inversion of d-NNA was performed in a two-step pathway by d-amino acid oxidase (DAAO) followed by an unidentified transaminase. Such chiral inversion contributes (at least partially) to the pharmacokinetic stereoselectivity of NNA. This study used the selective inhibitor of DAAO, sodium benzoate, to test the above hypothesis. An i.v. bolus injection of d-NNA (32 mg/kg) and l-NNA (16 mg/kg) in conscious rats exhibited biphasic disposition with different pharmacokinetic parameters in a stereospecific manner (approximately 5-10-fold differences). Unidirectional chiral inversion of d-NNA but not l-NNA was found from these animals. In addition to its similar inhibitory effects on the d-NNA conversion and DAAO activity in kidney homogenates, sodium benzoate completely blocked chiral inversion of d-NNA and led to a smaller stereospecific difference, reflected by a nearly 50% reduction of d-NNA clearance and a 2-fold increase in t(1/2) and area under the curve of d-NNA in benzoate-pretreated rats. The results suggest that DAAO plays an essential role in chiral inversion of d-NNA and chiral inversion contributes mostly to the pharmacokinetic stereospecificity of NNA.

Vascular contractile effect of urotensin II in young and aged rats: influence of aging and contribution of endothelial nitric oxide

To elucidate whether aging influences the vascular contractile effect of urotensin II in rat thoracic aorta, and to evaluate the contribution of endothelial vasodilating substances in mediating the effect of urotensin II, the effect of urotensin II was examined in the vessels of young (2-3-month-old) and aged rat. Isolated rat aortic rings incubated in Krebs-Henseleit solution gassed with 95% O2/5% CO2 were stimulated with urotensin II, and the developed tension was measured. Urotensin II increased the developed tension, which was decreased by aging. In 2-3-months-old young aorta without endothelium, urotensin II (10(-10) to 10(-7)) elicited a concentration-dependent aortic contraction to the maximal response almost equivalent to high KCl-induced contraction (79.4+/-11.3% of KCl(max)). In the presence of endothelium, the urotensin II-induced vasoconstriction in young aorta was significantly attenuated to 33.3+/-4.6% of KCl(max). However, the contractile response was greater in the pretreatment with N(G)-nitro-L-arginine (L-NNA) (100 microM) (50.3+/-8.4% of KCl(max) in endothelial denuded aorta), suggesting the vasorelaxing role of endothelial nitric oxide. In 25-27-months-old aged rat aorta, the urotensin II-mediated contraction was remarkably decreased, both in the presence (6.3+/-2.0% of KCl(max)) and absence (11.7+/-3.0% of KCl(max)) of endothelium. A cyclooxygenase inhibitor, diclofenac (10 microM), did not have any effect on the urotensin II-induced contraction. These results suggest that urotensin II can induce vascular smooth muscle contraction in rat aorta, and there was an aging-related decline in the urotensin II-induced contraction. Endothelial production of nitric oxide in response to urotensin II but not cyclooxygenase metabolites such as prostacyclin may play a role in reducing the vascular constriction especially in young aorta.

Chlamydia pneumoniae induces nitric oxide synthase and lipoxygenase-dependent production of reactive oxygen species in platelets. Effects on oxidation of low density lipoproteins

There is increasing evidence that Chlamydia pneumoniae is linked to atherosclerosis and thrombosis. In this regard, we have recently shown that C. pneumoniae stimulates platelet aggregation and secretion, which may play an important role in the progress of atherosclerosis and in thrombotic vascular occlusion. The aims of the present study were to investigate the effects of C. pneumoniae on platelet-mediated formation of reactive oxygen species (ROS) and oxidation of low-density lipoprotein (LDL) in vitro. ROS production was registered as changes in 2',7'-dichlorofluorescin- fluorescence in platelets with flow cytometry. LDL-oxidation was determined by measuring thiobarbituric acid reactive substances (TBARs). We found that C. pneumoniae stimulated platelet production of ROS. Polymyxin B treatment of C. pneumoniae, but not elevated temperature, abolished the stimulatory effects on platelet ROS-production, which suggests that chlamydial lipopolysaccharide has an important role. Inhibition of nitric oxide synthase with nitro-L-arginine, lipoxygenase with 5,8,11-eicosatriynoic acid and protein kinase C with GF 109203X significantly lowered the production of radicals. In contrast, inhibition of NADPH-oxidase with di-phenyleneiodonium (DPI) did not affect the C. pneumoniae induced ROS-production. These findings suggest that the activities of nitric oxide synthase and lipoxygenase are the sources for ROS and that the generation is dependent of the activity of protein kinase C. The C. pneumoniae-induced ROS-production in platelets was associated with an extensive oxidation of LDL, which was significantly higher compared to the effect obtained by separate exposure of LDL to C. pneumoniae or platelets. In conclusion, C. pneumoniae interaction with platelets leading to aggregation, ROS-production and oxidative damage on LDL, may play a crucial role in the development of atherosclerotic cardiovascular disease.

Nitric oxide synthesis is blocked in the enteral nervous system during dormant periods of the snail Helix lucorum

During dormancy of terrestrial snails, the whole neuromodulation of the nervous system is deeply modified. In this work we studied the adaptation of a previously described, putatively nitric oxide (NO) forming enteral network to the long-term resting periods of the snail Helix lucorum. The standard NADPH diaphorase (NADPHd) technique, which is an accepted method for histochemical NO synthase (NOS) detection, labeled the same enteric neurons of the midintestine in active or hibernated snails. Quantification of the NO-derived nitrite by the Griess reaction established that the nitrite formation is confined to the NADPHd-reactive network containing the midintestinal segment. In active snails, the nitrite formation could be enhanced by the NOS substrate L-arginine (10 microM-1 mM), but decreased by the known NOS inhibitors 1 mM N(omega)-nitro-L-arginine (NOARG) and 10 mM aminoguanidine (AG). Application of 1 mM L-arginine and 1 mM NOARG decreased the amplitude of the midintestinal muscle contractile activity, but did not affect the rectal motility. In dormancy, the nitrite formation was reduced in the NADPHd-reactive midintestinal network. Application of l-arginine could not provoke nitrite production and did not influence the midintestinal motility. Our findings indicate that NO is involved in the neural transmission to intestinal muscles of gastropods, but enteric release of NO is blocked during dormancy. The decreased NO synthesis is possibly due to an as yet undefined mechanism, by which the L-arginine/NO conversion ability of NOS could temporarily be inhibited in the long-term resting period of H. lucorum.

Structures of the Neuronal and Endothelial Nitric Oxide Synthase Heme Domain with d-Nitroarginine-Containing Dipeptide Inhibitors Bound

In a continuing effort to unravel the structural basis for isoform-selective inhibition of nitric oxide synthase (NOS) by various inhibitors, we have determined the crystal structures of the nNOS and eNOS heme domain bound with two D-nitroarginine-containing dipeptide inhibitors, D-Lys-D-Arg(NO)2-NH(2) and D-Phe-D-Arg(NO)2-NH(2). These two dipeptide inhibitors exhibit similar binding modes in the two constitutive NOS isozymes, which is consistent with the similar binding affinities for the two isoforms as determined by K(i) measurements. The D-nitroarginine-containing dipeptide inhibitors are not distinguished by the amino acid difference between nNOS and eNOS (Asp 597 and Asn 368, respectively) which is key in controlling isoform selection for nNOS over eNOS observed for the L-nitroarginine-containing dipeptide inhibitors reported previously [Flinspach, M., et al. (2004) Nat. Struct. Mol. Biol. 11, 54-59]. The lack of a free alpha-amino group on the D-nitroarginine moiety makes the dipeptide inhibitor steer away from the amino acid binding pocket near the active site. This allows the inhibitor to extend into the solvent-accessible channel farther away from the active site, which enables the inhibitors to explore new isoform-specific enzyme-inhibitor interactions. This might be the structural basis for why these D-nitroarginine-containing inhibitors are selective for nNOS (or eNOS) over iNOS.

Involvement of L-arginine-nitric oxide system in the response of isolated trachea to reactive oxygen species

The aim of this study was to investigate the effect of reactive oxygen species (ROS), generated by electrolysis of Krebs-Henseleit solution (GE-KHS), on isolated guinea pig trachea and to assess the possible involvement of nitric oxide (NO) in the observed effects. The isolated trachea was superfused in GE-KHS, generating H2O2 and hypochlorous acid (HOCl), both of which slowly increased in the organ bath and reached final stable concentrations of 42 and 63 microM, respectively, at the rate of 20 ml/min(-1), and 261 and 245 microM, respectively, at the rate of 5 ml/min(-1). ROS GE-KHS-induced relaxation of tracheal rings was preceded by a small transient contraction in 40% and 65% of experiments when tracheal rings were superfused at the rate of 20 ml/min(-1) and 5 ml/min(-1), respectively. Removal of tracheal epithelium abolished the relaxation of the trachea induced by ROS GE-KHS and unmasked or potentiated trachealis contraction. The ROS GE-KHS-induced changes in trachealis tension were accompanied by an increase in thiobarbituric acid reactive substances (TBARS) and a decrease in nonprotein (NP) thiols in the trachea. These changes were inhibited by treatment with the antioxidant N-acetylcysteine (100 microM). Pretreatment of tracheal rings with the inhibitor of NO synthase (NOS) N(omega)-nitro-L-arginine (L-NOARG; 100 microM) for 20 min prior to exposure to ROS GE-KHS decreased the ROS GE-KHS-induced relaxation. When L-NOARG (100 microM) was present in the superfusing solution, not only 20 min before but also during superfusion with ROS GE-KHS, the evoked trachealis relaxation was reduced in the first 15 min but was enhanced in the 30th min. This late enhancement of relaxation was accompanied by a 12-fold increase in nitric oxide metabolites (NO(x)). ROS GE-KHS-induced elevation of TBARS levels in the trachea was decreased to 63% by pretreatment with L-NOARG (100 microM). Elevation of TBARS levels induced by incubation of brain liposomes with a hydroxyl radical generating system was decreased to 90% by L-NOARG (10, 100 microM), while the antioxidant stobadine (100 microM) nearly completely inhibited the evoked lipid peroxidation. In comparison with Trolox, L-NOARG exerted a slight scavenging effect on the 1,1-diphenyl-2-picrylhydrazyl radical. The presence of L-arginine and D-arginine in the superfusion fluid for 15-20 min before and during exposure of the trachea to ROS GE-KHS inhibited trachealis relaxation. Results indicate that epithelium derived NO may participate in the response of guinea pig trachea to ROS GE-KHS. The presence of L-NOARG in the bathing fluid during superfusion with ROS GE-KHS gave rise to NO(x), with relaxing activity. L- and D-arginine induced an inhibition of the relaxatory response to ROS GE-KHS and partially prevented a ROS-induced decrease in NP thiols. The involvement of the small antioxidant effects of L-NOARG and L- and D-arginine in the above mentioned actions of L-NOARG and L-arginine requires additional investigation.

Influence of heme and heme oxygenase-1 transfection of pulmonary microvascular endothelium on oxidant generation and cGMP

Heme is a co-factor required for the stimulation of soluble guanylate cyclase (sGC) by nitric oxide (NO) and carbon monoxide, and sGC activation by these agents is inhibited by superoxide. Because heme promotes oxidant generation, we examined the influence of rat pulmonary microvascular endothelial cells (PMECs) with a stable human heme oxygenase-1 (HO-1) transfection and heme on oxidant generation and cGMP. Culture of PMEC with low serum heme decreased cGMP and the detection of peroxide with 10 microM 2',7'-dichlorofluorescin diacetate and increased HO-1 further decreased cGMP without altering the peroxide detection under these conditions. Under conditions where heme (30 microM) has been shown to stimulate cGMP production in PMECsby mechanisms involving NO and CO, heme increased the detection of peroxide in a PMEC-dependent manner and HO-1 transfection did not markedly alter the effects heme on peroxide detection. The addition of 1 microM catalase markedly inhibited the effects of heme on peroxide detection whereas increasing (0.1 mM ebselen) or decreasing (depleting glutathione with 7 mM diethylmaleate) rates of intracellular peroxide metabolism or inhibiting the biosynthesis of oxidants (with 10 microM diphenyliodonium or 0.1 mM nitro-L-arginine) had only modest effects. The detection of superoxide by 10 microM dihydroethidium from PMECs was not increased by exposure to heme. These actions of oxidant probes suggest that intracellular oxidants have a minimal influence on the response to heme. Thus, exposure of PMECs to heme causes a complex response involving an extracellular generation of peroxide-derived oxidant species, which do not appear to originate from increases in intracellular superoxide or peroxide. This enables heme and HO to regulate sGC through mechanisms involving NO and CO, which are normally inhibited by superoxide.

The effects of antioxidants and nitric oxide modulators on hepatic ischemic-reperfusion injury in rats

Ischemic-reperfusion injury (IRI) is thought to be caused by oxygen radicals. Nitric oxide (NO) also has been thought to play a key role in IRI. This experiment was designed to evaluate the effects of antioxidants and NO supplement on hepatic IRI. Male Sprague-Dawley rats were divided into five groups: a sham operation group, a group with IRI, and three groups with vitamin C combined with vitamin E (VC&VE), L-arginine and N(G)-nitro-L-arginine (NNLA) injected after IRI. IRI was induced by clamping of the porta hepatis for 30 minutes and then by declamping. To prevent mesenteric blood congestion, a porto-systemic shunt had been made four weeks before the portal clamping. Biochemical assays of TNF-alpha level and NO2- level in the blood, malondialdehyde level, catalase activity and NO synthase activity in the liver tissue were performed. The results were as follows: IRI increased the malondialdehyde level and exhausted the catalase activity remarkably. VC&VE lowered the malondialdehyde levels and protected against catalase exhaustion, but had no significant effect on the NO production. L-arginine had a definite antioxidant effect, which was much weaker than that of VC&VE. In conclusion, antioxidants and a supplement of NO protected the liver tissue against IRI.

A brain nitric oxide synthase study in the rat: production of a nitroso-compound NA and absence of nitric oxide synthesis

The products of brain NO-synthase (NOS) were studied by different analytical techniques with the same incubation conditions. Voltammetric techniques used a micro cell containing NOS and its substrate (10 mM arginine). Using porphyrin microelectrodes with differential pulse amperometry nitric oxide (NO) was not detected when nafion membrane was present (less than 0.3 muM). Nitrite was detected with the same microelectrode without membrane (0.42 mM). Differential pulse voltammetry (DPV) with micro carbon electrode detected a nitroso-compound (NA) in reduction (1 mM) and not NO. In oxidation the observed DPV peak was due to nitrite (0.43 mM). Citrulline was detected by high performance liquid chromatography (0.51 mM). Using Diels Alder reaction in NOS preparation a NA-cycloadduct was observed by capillary electrophoresis (0.2 mM) and mass spectrometry (0.22 mM). Diels Alder reaction is the reaction of the identification of the nitroso group. NA-cycloadduct degradation by retro Diels Alder reaction gave equimolar concentrations of citrulline and nitrite without NO production. These observations lead us to affirm that NOS synthesizes NA.

N(omega)-arginine dimethylation modulates the interaction between a Gly/Arg-rich peptide from human nucleolin and nucleic acids

We studied the interaction between a synthetic peptide (sequence Ac-GXGGFGGXGGFXGGXGG-NH(2), where X = arginine, N(omega),N(omega)-dimethylarginine, DMA, or lysine) corresponding to residues 676-692 of human nucleolin and several DNA and RNA substrates using double filter binding, melting curve analysis and circular dichroism spectroscopy. We found that despite the reduced capability of DMA in forming hydrogen bonds, N(omega),N(omega)-dimethylation does not affect the strength of the binding to nucleic acids nor does it have any effect on stabilization of a double-stranded DNA substrate. However, circular dichroism studies show that unmethylated peptide can perturb the helical structure, especially in RNA, to a much larger extent than the DMA peptide.

Axonal transport of NADPH-diaphorase and [(3)H]nitro-L-arginine binding, but not [(3)H]cGMP binding, by the rat vagus nerve

Previous studies have shown that the NO(ccirf)-cGMP pathway may be functionally relevant in the nodose ganglion and at afferent terminations of the vagus nerve. The technique of unilateral vagal ligations, using double ligatures, was combined with the techniques of NADPH-diaphorase histochemistry, as an index of nitric oxide synthase (NOS) activity, and autoradiography using the radioligands [(3)H]nitro-L-arginine and [(3)H]cGMP, to examine axonal transport of NOS and cGMP-dependent effectors by the rat vagus nerve. A population of perikarya in the nodose ganglia was NADPH-diaphorase positive, and binding of both [(3)H]nitro-L-arginine and [(3)H]cGMP was found on the nodose ganglia. Following vagal ligation, NADPH-diaphorase reactivity accumulated proximal to the proximal ligature and distal to the distal ligature. Vagus nerve transection beyond the distal ligature eliminated NADPH-diaphorase reactivity at the distal ligature. Similarly, [(3)H]nitro-L-arginine binding was found over the nodose ganglion; and after vagal ligation, an accumulation of [(3)H]nitro-L-arginine binding was seen adjacent to the proximal ligature, though little binding was found adjacent to the distal ligature. No accumulation of [3H]cGMP binding was found adjacent to either the proximal or the distal ligatures. These findings suggest that the rat vagus nerve bidirectionally transports NOS, the enzyme involved in biosynthesis of NO(ccirf) by nitroxidergic nerves. As anticipated, [(3)H]nitro-L-arginine, a competitive inhibitor of the amino acid precursor for NO(ccirf), binds only to a centrifugally transported moiety that we conjecture is NOS, while cGMP apparently is not subject to transport. These data further support the use of NO(&z.ccirf;) in transmission at vagal afferent terminals.

Expression of nitric oxide synthase isoforms in spinal cord in amyotrophic lateral sclerosis

METHODS

Autoradiography with [3H]nitro-L-arginine (3HL-NNA) was used to quantify nitric oxide synthase (NOS), and immunocytochemistry to identify NOS isoforms, in spinal cord in amyotrophic lateral sclerosis (ALS) and controls.

RESULTS

In controls NOS binding was marked only in the superficial dorsal horn, but in ALS tissue it was intense throughout the grey and white matter. A single population of binding sites was indicated in controls, but two populations in ALS. In the controls intense neuronal NOS (nNOS) immunoreactivity was present in numerous cells in the dorsal horn, and faint immunoreactivity in small and medium-sized cells in the ventral horn. Only weak immunoreactivity for inducible NOS (iNOS) and endothelial NOS (eNOS) was detectable in control tissue. In ALS, the pattern was broadly similar in the grey matter, but immunoreactivity for both nNOS and iNOS was present in white matter.

CONCLUSION

Expression of abnormal variants of nNOS or increased expression of iNOS may have a role in motoneuron death in ALS.

Up-regulation of endothelin (ET(A) and ET(B)) receptors and down-regulation of nitric oxide synthase in the detrusor of a rabbit model of partial bladder outlet obstruction

Bladder outlet obstruction (BOO) is associated with altered bladder structure and function. Endothelin-1 (ET-1) has mitogenic and potent contractile properties. There are two ET receptors: ET(A) and ET(B). Nitric oxide synthase (NOS) is the enzyme responsible for the synthesis of nitric oxide (NO) which is involved in smooth muscle relaxation. We investigated whether there are any changes in the density of ET-receptors and NOS in the detrusor and bladder neck in a rabbit model of BOO. Partial BOO was induced in adult male New Zealand White rabbits. Sham operated age-matched rabbits acted as controls. After six weeks the urinary bladders were excised and detrusor and bladder neck sections incubated with radioligands for ET-1, ET(A) and ET(B) receptors and with [3H]-1-NOARG (a ligand for NOS). NADPH histochemistry was also performed. BOO bladder weights were significantly increased (P = 0.002). ET-1 binding and ETA receptor binding sites were significantly increased in the BOO detrusor smooth muscle (P = 0.04, P = 0.03 respectively) and urothelium (P = 0.002, P = 0.02 respectively). ET(B) receptor binding sites were also significantly increased in the BOO detrusor smooth muscle (P = 0.04). However, there was no change in the BOO bladder neck. NOS was significantly decreased in the detrusor smooth muscle (P = 0.003) and urothelium (P = 0.0002). In the bladder neck NOS was also significantly reduced in the urothelium (P = 0.003). NADPH staining was decreased in the detrusor and bladder neck. The up-regulation of ET receptors along with the down-regulation of NOS in the detrusor may contribute to the symptoms associated with BOO. Since ET-1 has a mitogenic role, especially via its ETA receptors, the increase in ETA receptors may also be involved in detrusor hyperplasia and hypertrophy in BOO. ET antagonists may therefore have a role in the treatment of patients with BOO.

No detectable NO synthesis from L-arginine or N(G)-hydroxy-L-arginine in fMLP-stimulated human blood neutrophils despite production of nitrite, nitrate, and citrulline from N(G)-hydroxy-L-arginine

Nitric oxide (NO) is a well-documented effector molecule in rodent phagocytes but its synthesis in human neutrophils has been controversial. In this study, NO production in human neutrophils activated by chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP) was measured in the presence of L-arginine (L-Arg) and N(G)-hydroxy-L-arginine (OH-L-Arg), the precursor and intermediate amino acids in NO synthesis, respectively. Incubation of fMLP-activated neutrophils with OH-L-Arg resulted in a production of nitrite, nitrate, and citrulline that was greater than with unstimulated neutrophils but was not inhibited by the NOS inhibitors L-NMMA and L-NIO or the cytochrome P450 inhibitor troleandomycin and was not seen when OH-L-Arg was replaced with L-Arg. This nitrite, nitrate, and citrulline production was not associated with any detectable NO synthesis because no increases in cyclic GMP were observed in the presence of phosphodiesterase inhibitors and in the presence or absence of superoxide dismutase. Moreover, no increases in the formation of the reaction product of NO with superoxide, peroxynitrite, were observed on addition of either OH-L-Arg or L-Arg to activated neutrophils, as assessed either by dihydrorhodamine oxidation or protein nitration. This suggests that, in spite of the production of nitrite, nitrate, and citrulline, commonly used indicators of NO formation, normal human blood neutrophils, are not producing detectable amounts of either NO or peroxynitrite when stimulated with fMLP in the presence of OH-L-Arg.

An experimental, NADPH-diaphorase histochemical and immunocytochemical study of Mesocestoides vogae tetrathyridia

In order to test the role of nitric oxide in flatworms, Mesocestoides vogae tetrathyridia were incubated together with L-arginine, which is the substrate for nitric oxide synthesis, or with NG-nitro-L-arginine, which is an irreversible inhibitor of nitric oxide synthase. Normally, tetrathyridia attach to each other with the aid of their suckers, forming clusters. The rate of cluster formation was followed during the incubations. L-Arginine stimulated, and NG-nitro-L-arginine clearly inhibited, the cluster formation. This is the first time that an effect of nitric oxide has been observed in a flatworm. In addition, the pattern of the NADPH-diaphorase histochemical reaction in the nervous system and the pattern of F-actin filaments in the musculature stained with TRITC-labelled phalloidin were studied. NADPH-d staining occurred in the brain and the main nerve cords but also followed the muscle fibres stained with phalloidin. The pattern of the NADPH-d reaction was compared with that of 5-HT immunoreactivity. The implications of the results are discussed in relation to the background of data on neuronal signal substances in M. vogae.

Increases in [3H]FK-506 and [3H]L-N(G)-nitro-arginine binding in the rat brain after nigrostriatal dopaminergic denervation

Receptor autoradiographic technique was studied to investigate sequential changes in FK-506 binding proteins, nitric oxide synthase and dopamine uptake sites in the brain 1 week to 8 weeks after unilateral 6-hydroxydopamine injection of the medial forebrain bundle in rats. [3H]FK-506, [3H]L-N(G)-nitro-arginine and [3H]mazindol were used to label FK-506 binding proteins (immunophilin), nitric oxide synthase and dopamine uptake sites, respectively. [3H]FK-506 binding showed about 13-25% increase in the ipsilateral striatum from 2 to 8 weeks after degeneration of nigrostriatal pathway. However, no significant change in [3H]FK-506 binding was observed in the ipsilateral substantia nigra during the postlesion periods. In the contralateral side, [3H]FK-506 binding also showed about 13-25% increase in the striatum from 2 to 8 weeks postlesion. The substantia nigra showed a 21% increase in [3H]FK-506 binding only 2 weeks after the lesioning. On the other hand, [3H]L-N(G)-nitro-arginine binding showed about 21-31% increase in the parietal cortex and striatum 1 week or 2 weeks postlesion. In the contralateral side, a 21% increase in [3H]L-N(G)-nitro-arginine binding was found in the dorsolateral striatum only 1 week postlesion. In contrast, degeneration of nigrostriatal pathway caused a conspicuous loss of [3H]mazindol binding in the ipsilateral striatum (87-96%), substantia nigra (36-73%) and ventral tegmental area (91-100%) during the postlesion periods. In the contralateral side, no significant changes in [3H]mazindol binding were observed in these areas up to 8 weeks after the postlesion. The present study demonstrates that unilateral injection of 6-hydroxydopamine into the medial forebrain bundle of rats can cause a significant increase in [3H]FK-506 and [3H]L-N(G)-nitro-arginine bindings in the brains. In contrast, a marked reduction in [3H]mazindol binding is observed in the brains after the lesioning, indicating severe damage to nigrostriatal dopaminergic pathway. These results suggest that immunophilin and nitric oxide synthase may play some role in the pathogenesis of neurodegenerative disorders such as Parkinson's disease.

The in vivo unidirectional conversion of nitro-D-arginine to nitro-L-arginine

We recently reported that nitric oxide synthase in the brain can be inhibited not only by nitro-L-arginine (L-NA) but also by its D-enantiomer nitro-D-arginine (D-NA). In the present study, we found that D-NA, when tested in vitro, was 400 times less potent than L-NA. However, when D-NA was injected in vivo, its L-enantiomer, L-NA, was found to rapidly appear in plasma samples (approximately 1 min), rose to a maximum concentration at 30 min (approximately 40% conversion), and remained at this plateau for about 5 h. This was consistent with the changes in blood pressure. There was no conversion of L- to D-NA. The results suggested that D-NA has very weak biological actions by itself, but when administered in vivo, D-NA can be converted to L-NA.

[Activation of L-Arg: no pathway in canine brain by the damage from complete cerebral ischemia-reperfusion]

To ascertain whether complete cerebral ischemia-reperfusion activate L-Arg: NO pathway in canine brain, we anestherized nine adult dogs with ketamine and fentayle and randomly divided into two groups. Four dogs were nonischemic control group. Five dogs were complete cerebral ischemia-reperfusion group, they underwent a 18-minute cardiac arrest, and were resusciatation by standard CPR, supported by intensive care for 8 hours. At the end of each experiment, the parietal cortex was assayed for content of Nitrite and NADPH-positive neurons. Compared with the control group, the contents of Nitrite and NADPH-positive neurons of coxtex in complete cerebral ischemia-reperfusion group increased significantly (P < 0.01). The results suggest that complete cerebral ischemia-reperfusion activate the L-Arg: NO pathway in canine brain, and NO may play an important role in cerebral ischemia-reperfusion injury.

Expression of nitric oxide synthase in the spinal cord in amyotrophic lateral sclerosis

The expression of nitric oxide synthase was studied in human postmortem cervical spinal cord from four individuals with amyotrophic lateral sclerosis (ALS) and four individuals who had died from non-neurological causes. A novel autoradiographic method employing [3H]nitro-L-arginine, a potent inhibitor of the enzyme, as the binding ligand, was used. The expression was quantified in four discrete subregions of the grey matter, and in the dorsal and ventral white matter. The maximum density of binding in the superficial dorsal, deeper dorsal horn, and intermediate subregions of the grey matter was similar in ALS and control tissue, but it was higher in the ALS tissue, in the ventral horn, and in the dorsal and ventral white matter, compared to the corresponding regions in the control tissue. Saturation analysis of the binding indicated a single population of high affinity binding sites in all subregions in the control tissue. However, in the ALS tissue, in all subregions, the presence of two populations of binding sites with different ligand binding affinities were indicated. It is possible therefore that the expression of an inducible isotype of nitric oxide synthase may contribute to the neuropathic changes seen in ALS.

Synthesis and screening of conformationally restricted and conformationally free N-(tertiary aminoalkyl)dithiocarbamic acids and esters as inhibitors of neuronal nitric oxide synthase

N-(Tertiary aminoalkyl)dithiocarbamic acids and esters were synthesized and evaluated for their ability to inhibit neuronal nitric oxide synthase. Preliminary results show these compounds are able to act at the binding site for L-arginine and the conformationally restricted esters may have a second site of activity involving the cofactor (6R)-5,6,7,8-tetrahydro-L-biopterin.

Distribution and metabolism of N(G)-nitro-L-arginine methyl ester in patients with septic shock

OBJECTIVE

The pharmacokinetics of N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, was investigated in patients with septic shock.

METHODS

Blood was sampled at intervals before, during and after 12-h infusion of L-NAME 1 mg x kg(-1) x h(-1) in nine septic shock patients for determination of plasma concentrations by high-performance liquid chromatography (HPLC). In three patients the renal clearance of the drug was determined.

RESULTS

Incubation of L-NAME with plasma and blood in vitro revealed hydrolysis to N(G)-nitro-L-arginine (L-NOARG), the active inhibitor of NO synthesis. L-NOARG did not undergo further degradation. Continuous intravenous infusion of 1 mg x kg(-1) x h(-1) of L-NAME for 12 h in patients with septic shock increased blood pressure and resulted in increasing plasma concentrations of L-NOARG (Cmax 6.2 microg x ml(-1) at 12 h) whereas L-NAME concentrations reached a plateau within 1.5 h (Cmax 1.0 microg x ml(-1)). After the infusion was stopped L-NAME disappeared from the plasma rapidly (half-life 19.2 min) whereas L-NOARG concentration declined slowly (half-life 22.9 h). The calculated volume of distribution for L-NAME was 0.451 x kg(-1) body weight and 1.961 x kg(-1) for L-NOARG. The renal clearance for L-NOARG was 3.5% of total body clearance for L-NOARG, whereas L-NAME could not be detected in urine.

CONCLUSION

We conclude that vasoconstriction with L-NAME in septic patients may result from hydrolysis to L-NOARG, the active inhibitor of NO synthesis. The long plasma half-life and large volume of distribution for L-NOARG suggests extensive distribution to extravascular tissues. Since renal excretion is minimal, elimination of the metabolite L-NOARG follows other pathways.

Haem insertion, dimerization and reactivation of haem-free rat neuronal nitric oxide synthase

The nitric oxide synthases are dimeric enzymes in which the intersubunit contacts are formed by the P-450-haem-containing, tetrahydrobiopterin-dependent oxygenase domain. The dimerization of the neuronal isoenzyme was shown previously to be triggered by Fe-protoporphyrin IX (haemin). We report for the first time the reactivation of the haem-deficient neuronal isoenzyme (from rat, expressed in a baculovirus/insect cell system) after haem reconstitution. We further examined the reconstitution of the enzyme with protoporphyrin IX (PPIX) and its Mn and Co complexes. All of these porphyrins inserted into the haem pocket, as assessed by quenching of intrinsic protein fluorescence. In addition to haemin, MnPPIX stimulated dimerization, as measured by gel filtration and by cross-linking with glutaraldehyde. In contrast, neither CoPPIX nor PPIX stimulated dimerization. The absorbance spectra of the reconstituted enzymes were measured and compared with published results on P-450 enzymes reconstituted with the same metals. The results suggest that those metalloporphyrins which caused dimerization were able to acquire a thiolate ligand from the protein, and we propose that this ligation is the trigger for dimerization. Substrate and tetrahydrobiopterin binding sites only emerged with the metalloporphyrins that caused dimerization.

Nitroarginine and tetrahydrobiopterin binding to the haem domain of neuronal nitric oxide synthase using a scintillation proximity assay

Nitric oxide synthases (NOS) have a bidomain structure comprised of an N-terminal oxygenase domain and a C-terminal reductase domain. The oxygenase domain binds haem, (6R)-5,6,7,8-tetrahydro-l-biopterin (tetrahydrobiopterin) and arginine, is the site where nitric oxide synthesis takes place and contains determinants for dimeric interactions. A novel scintillation proximity assay has been established for equilibrium and kinetic measurements of substrate, inhibitor and cofactor binding to a recombinant N-terminal haem-binding domain of rat neuronal NOS (nNOS). Apparent Kd values for nNOS haem-domain-binding of arginine and Nomega-nitro-L-arginine (nitroarginine) were measured as 1.6 microM and 25 nM respectively. The kinetics of [3H]nitroarginine binding and dissociation yielded an association rate constant of 1.3x10(4) s-1.M-1 and a dissociation rate constant of 1.2x10(-4) s-1. These values are comparable to literature values obtained for full-length nNOS, suggesting that many characteristics of the arginine binding site of NOS are conserved in the haem-binding domain. Additionally, apparent Kd values were compared and were found to be similar for the inhibitors, L-NG-monomethylarginine, S-ethylisothiourea, N-iminoethyl-L-ornithine, imidazole, 7-nitroindazole and 1400W (N-[3-(aminomethyl) benzyl] acetamidine). [3H]Tetrahydrobiopterin bound to the nNOS haem domain with an apparent Kd of 20 nM. Binding was inhibited by 7-nitroindazole and stimulated by S-ethylisothiourea. The kinetics of interaction with tetrahydrobiopterin were complex, showing a triphasic binding process and a single off rate. An alternating catalytic site mechanism for NOS is proposed.

Biological activation of N(G)-nitro-D-arginine by kidney homogenate

N(G)-nitro-L-arginine (L-NNA) and D-NNA have been shown to inhibit endothelium-dependent relaxation. This study examined if the inhibitory effect of L-NNA or D-NNA on relaxation is increased following incubation of the drug with the supernatant of tissue homogenates. Acetylcholine (ACh) caused concentration-dependent relaxation of pre-constricted rat aortic rings with maximum relaxation of 95%. Maximum relaxations to ACh were reduced to 71 and 37% in the presence of D-NNA (40 microM) and L-NNA (1 microM), respectively. Relaxation to ACh was further reduced to 18% in the presence of D-NNA that was incubated for 1 h with the supernatant of kidney homogenate, but unaffected by D-NNA incubated with the supernatant of trichloroacetic acid-denatured kidney homogenate. Incubation of L-NNA (1 microM) with either kidney supernatant or denatured kidney supernatant for 1 h did not affect its inhibitory effect on ACh-induced relaxation. Neither 1 h's incubation with plasma, or supernatants of liver, lungs or aorta homogenates affected the inhibitory action of D-NNA (40 or 120 microM) on ACh-induced relaxation. After D-NNA was incubated in kidney supernatant, its inhibitory effect on ACh-induced relaxation of the aorta was abolished by pretreatment of the aorta with L-arginine (L-Arg) but not D-Arg suggesting involvement of the L-Arg pathway. The results suggest that D-NNA is converted by the kidney to a compound that acts similar to L-NNA. There appears to be little conversion of L-NNA to D-NNA.

Substrate and substrate analog binding to endothelial nitric oxide synthase: electron paramagnetic resonance as an isoform-specific probe of the binding mode of substrate analogs

The binding of arginine analogs to endothelial nitric oxide synthase (eNOS, NOSIII) perturbs the environment of the high-spin ferriheme in a highly ligand-specific manner. Using electron paramagnetic resonance as a probe of heme ligation geometry, four categories of high-spin complex could be distinguished. These are analogous to the four classes of high-spin complexes, stabilized individually by the binding of L-arginine, N-hydroxy-L-arginine (NHA), N-methyl-L-arginine (NMA), and N-nitro-L-arginine (NNA), which we have previously reported for the other two isoforms. Each of these species is five-coordinate and retains the axial thiolate ligand but each differs in its ligation geometry. N-Methyl-L-arginine is a relatively poor inhibitor of eNOS, and the NMA complex of eNOS differs from the N-methyl-L-arginine complexes of inducible nitric oxide synthase (iNOS, NOSII) and neuronal nitric oxide synthase (nNOS, NOSI) in that it is of lower rhombicity. We previously showed that inducible nitric oxide synthase, which binds NNA less tightly than eNOS and nNOS, could not form the lower rhombicity NNA complex characteristic of nNOS. Endothelial nitric oxide synthase readily forms such lower rhombicity complexes, which correlates with the tight binding of NNA to this isoform. Arginine and tetrahydrobiopterin promote loss of the flavin free radical EPR signal, while arginine analog inhibitors stabilize the radical; this suggests that the residual flavin radicals can serve as a source of reducing equivalents for slow turnover in the absence of endogenous reductant.

[Effects of no precursor and donor on neuronal activity of rat hippocampal slices]

Using extracellular recording technique, the effects of L-arginine (L-arg), N-nitro-L-arginine (L-NNA), SIN-1 and methylene blue (MB) on spontaneous discharges of neurons in CA1 area of hippocampal slices were examined to determine the role of L-arg: NO pathway and the possible underlying mechanism. The results were as follows: (1) In response to the application of L-arg (1 mmol/L) into the superfusate for 2 min, spontaneous discharge rate (SDR) of 42/54 (77.8%) neurons was decreased significantly, while that of 12/54 (22.2%) neurons showed no change. Following the application of L-NNA (0.15 mmol/L) into the superfusate for 2 min, SDR of 25/29 (86.2%) neurons was increased markedly and that of 4/29 (13.8%) neurons was not affected. The effect of L-NNA might be reversed by pretreatment with L-arg. (2) With application of NO donor SIN-1 (5 mmol/L), SDR of 25 (100%) neurons was decreased in a dose-dependent manner. (3) After superfusing the brain slice with guanylate cyclase inhibitor, MB (3 mumol/L) for 30 min, SDR of 10 units showed significant increase as compared with control. However, MB failed to abolish the effect of L-arg on hippocampal neurons. Taken together, it is likely that NO is released during the resting state of hippocampal neurons and may inhibit the activity of hippocampus, an effect not mediated by the action of guanylate cyclase.

Transport of L-arginine and the nitric oxide inhibitor NG-monomethyl-L-arginine in human erythrocytes in chronic renal failure

1. Transport of L-arginine and the nitric oxide synthase inhibitors NG-monomethyl-L-arginine and NG-nitro-L-arginine was investigated in human erythrocytes from healthy donors and uraemic patients on haemodialysis. 2. Although K(m) values for total L-arginine influx were not significantly different in erythrocytes freshly isolated from controls or uraemic patients, uraemia was associated with an increase in the Vmax for transport (826 compared with 1176 mumol h-1 l-1 of cells) which was reduced to control values after dialysis. 3. Saturable influx of L-arginine was mediated by the classical cationic amino acid transport system y+ and system y+L, known to transport cationic and neutral amino acids with higher affinity. 4. Under zero-trans conditions, the Vmax for L-arginine transport via system y+increased from 271 to 700 mumol h-1 l-1 of cells in uraemia, while K(m) values increased from 44 to 94 mumol/l. Dialysis had no significant effect on the kinetic parameters altered by uraemia. 5. Under zero-trans conditions, and with system y+ inhibited by N-ethylmaleimide (0.2 mmol/l), transport of L-arginine via system y+L was unaffected by uraemia. 6. Saturable influx of NG-monomethyl-L-arginine was also mediated by systems y+ (K(m) = 56 mumol/l, Vmax = 353 mumol h-1 l-1 of cells) and y+L (K(m) = 17 mumol/l, Vmax = 51.3 mumol h-1 l-1 of cells) and, as with L-arginine, uraemia increased the transport capacity for NG-monomethyl-L-arginine. 7. Influx of the neutral nitric oxide synthase inhibitor NG-nitro-L-arginine was not readily saturable. 8. Intracellular concentrations of L-arginine and NG-monomethyl-L-arginine were significantly increased in erythrocytes from uraemic patients when compared with controls, consistent with an increased transport capacity for L-arginine and NG-monomethyl-L-arginine. 9. The present study provides evidence that system y+ mediates the increased transport of L-arginine and NG-monomethyl-L-arginine in human erythrocytes from patients with chronic renal failure. Our findings may have implications for the activity of the L-arginine-nitric oxide signalling pathway in vascular endothelial and smooth-muscle cells in uraemia.

Effects of kyotorphin (L-tyrosyl-L-arginine) ON[3H]NG-nitro-L-arginine binding to neuronal nitric oxide synthase in rat brain

L-Tyrosyl-L-arginine (kyotorphin) is known as an endogenous analgesic neuropeptide. We examined whether kyotorphin and other arginine-containing neuropeptides were endogenous substrates for neuronal nitric oxide synthase (NOS) in the rat brain. Cytosol fractions of the rat cerebellum contained higher concentrations of neuronal NOS (nNOS) than endothelial NOS. In rat cerebellar cytosol, the binding activity of [3H]NG-nitro-L-arginine (NNA) was inhibited equally by L-arginine (L-Arg), kyotorphin, and L-leucyl-L-Arg (a kyotorphin receptor antagonist). Binding activities were inhibited to lesser degrees by fibronectin active fragments, bradykinin, and dynorphin A, but were not inhibited by L-tyrosyl-D-Arg or substance P. Interestingly, the inhibition of [3H]NNA binding by kyotorphin was attenuated by inhibitors of kyotorphin-hydrolyzing peptidases (KTPases) such as bestatin and arphamenine B. These results suggest that kyotorphin is degraded to L-Arg by KTPases, which in turn may act as substrate for nNOS.

Selective inhibitors of neuronal nitric oxide synthase--is no NOS really good NOS for the nervous system?

It is now ten years since NO was shown to account for the biological activity of endothelium-derived relaxing factor (EDRF). It is also the tenth anniversary of the identification of L-NG monomethyl arginine (L-NMMA) as the very first inhibitor of NO biosynthesis. That EDRF and NO were one and the same sparked an explosion of interest in the biochemistry and pharmacology of NO which has yet to subside. In contrast, the first ever nitric oxide synthase (NOS) inhibitor slipped seamlessly into the literature virtually without comment at the time. Over the following decade, L-NMMA (and like NOS inhibitors) have proved invaluable as tools for probing the biological roles of NO in health and disease and, in particular, have increased our understanding of the function of NO in the nervous system. Further advances in this important area now require the development of inhibitors selective for the neuronal isoform of NOS (nNOS). Here, Philip Moore and Rachel Handy provide an up-to-date account of the literature regarding the biochemical and pharmacological characterization of NOS inhibitors with particular reference to compounds with greater selectivity for the nNOS isoform.

Cysteine-200 of human inducible nitric oxide synthase is essential for dimerization of haem domains and for binding of haem, nitroarginine and tetrahydrobiopterin

Nitric oxide synthase (EC 1.14.13.39) is a homodimer. Limited proteolysis has previously shown that it consists of two major domains. The C-terminal or reductase domain binds FMN, FAD and NADPH. The N-terminal or oxygenase domain is known to bind arginine, (6R)-5,6,7,8-tetrahydro-l-biopterin (tetrahydrobiopterin) and haem. The exact residues of the inducible nitric oxide synthase (iNOS) protein involved in binding to these molecules have yet to be identified, although the haem moiety is known to be co-ordinated through a cysteine thiolate ligand. We have expressed two forms of the haem-binding domain of human iNOS (residues 1-504 and 59-504) in Escherichia coli as glutathione S-transferase (GST) fusion proteins. The iNOS 1-504 and 59-504 fusion proteins bound similar amounts of haem, Nomega-nitro-l-arginine (nitroarginine) and tetrahydrobiopterin, showing that the first 58 residues are not required for binding these factors. Using site-directed mutagenesis we have mutated Cys-200, Cys-217, Cys-228, Cys-290, Cys-384 and Cys-457 to alanine residues within the iNOS 59-504 haem-binding domain. Mutation of Cys-200 resulted in a complete loss of haem, nitroarginine and tetrahydrobiopterin binding. Mutants of Cys-217, Cys-228, Cys-290, Cys-384 or Cys-457 showed no effect on the haem content of the fusion protein, no effect on the reduced CO spectral peak (444 nm) and were able to bind nitroarginine and tetrahydrobiopterin at levels equivalent to the wild-type fusion protein. After removal of the GST polypeptide, the wild-type iNOS 59-504 domain was dimeric, whereas the C200A mutant form was monomeric. When the mutated domains were incorporated into a reconstructed full-length iNOS protein expressed in Xenopus oocytes, only the Cys-200 mutant showed a loss of catalytic activity: all the other mutant iNOS proteins showed near wild-type enzymic activity. From this systematic approach we conclude that although Cys-217, Cys-228, Cys-290, Cys-384 and Cys-457 are conserved in all three NOS isoforms they are not essential for cofactor or substrate binding or for enzymic activity of iNOS, and that Cys-200 provides the proximal thiolate ligand for haem binding in human iNOS.

NG-nitro-L-[3H]arginine binding properties of neuronal nitric oxide synthase in rat brain

NG-Nitro-L-arginine (L-NNA), a derivative of L-arginine (L-Arg), is known as a pseudosubstrate and inhibitor for nitric oxide synthase (NOS). To clarify the regulatory mechanism of substrate-binding domain in neuronal NOS (nNOS), we examined the characteristics of NG-nitro-L-[3H]Arg (L-[3H]NNA) binding using the cytosolic fraction and purified nNOS from the rat cerebellum, in comparison with L-[14C]citrulline formation from L-[14C]Arg. The L-[3H]NNA binding was inhibited by L-NNA > NG-methyl-L-Arg > diphenyleneiodonium > L-Arg, but was not inhibited by L-citrulline and D-Arg. Thus, L-NNA seems to bind the substrate-binding domain in the nNOS with high affinity rather than L-Arg. Even in the absence of NADPH, tetrahydrobiopterin (BH4) and Ca2+, the L-[3H]NNA binding activity was observed in the cerebellar cytosol, although L-[14C]citrulline could not be produced from L-[14C]Arg. L-[3H]NNA binding was increased by BH4 alone and was markedly enhanced by NADPH plus BH4 (NADPH/BH4), but not by Ca2+/CaM. In contrast, L-[14C]citrulline was formed only in the presence of NADPH/BH4 and Ca2+. Similar results were obtained in purified nNOS. These results suggest that L-[3H]NNA seems to bind the substrate-binding domain in the nNOS but the binding affinity of L-Arg was lower than the affinity of L-NNA. Although the substrate binding is necessary to BH4 and NADPH, Ca2+/CaM are further necessary for the formation of NO and L-citrulline.

Kinetics of the degradation of NG-nitro-L-arginine and its methyl ester in human umbilical vein blood and amniotic fluid

The kinetics of the degradation of the inhibitors of the nitric oxide synthesis, NG-nitro-L-arginine methyl ester and NG-nitro-L-arginine, were examined in human amniotic fluid and umbilical vein blood. The reaction rate constants were calculated or estimated using the time-controlled concentration course of both substances. These concentrations were measured by high-performance liquid chromatography with two different separation systems: ion-exchange chromatography and ion-pair chromatography. Using this method, either NG-nitro-L-arginine methyl ester and/or NG-nitro-L-arginine were added to 18 samples of amniotic fluid, 33 samples of plasma and 21 samples of uncentrifuged umbilical vein blood samples; subsequently these samples were used for measurement. The degradation of the two individual study substances can be described by a uni-unimolecular two-step consecutive reaction. Thereby, NG-nitro-L-arginine methyl ester decomposes to NG-nitro-L-arginine. Although NG-nitro-L-arginine decomposed further, the decomposition product could not be identified. The average of the reaction rate constants for NG-nitro-L-arginine methyl ester/NG-nitro-L-arginine was determined, yielding the following values: 0.032 h-1/0.00047 h-1 in amniotic fluid, 0.029 h-1/0.00384 h-1 and 0.00074 h-1 in plasma and 0.80 h-1/0.00060 h-1 in uncentrifuged umbilical vein blood. During the first hours after sampling, these reaction rate constants could be used to approximate the concentrations of NG-nitro-L-arginine methyl ester and NG-nitro-L-arginine at the time of sampling.

Evidence for mediation of L-2-chloropropionic acid-induced delayed neuronal cell death by activation of a constitutive nitric oxide synthase

1. Delayed neuronal cell death elicited by excess excitatory amino acid concentrations has been strongly implicated in many neurological disorders including head trauma, stroke, motor neurone disease and Huntington's disease. We have used the neurotoxin, L-2-chloropropionic acid (L-CPA) to model cellular events in vivo leading to delayed neuronal cell loss which is confined to the cerebellar cortex and can be prevented by inhibitors of nitric oxide synthase such as NG-nitro-L-arginine methyl ester. 2. Experiments were performed to determine whether the constitutive nitric oxide synthase (NOS) or inducible form of NOS (iNOS) was responsible for the neuronal cell death. Activation of NOS was confirmed by a 39% increase in cerebellar total nitrate and nitrite concentrations in L-CPA-treated brains, as compared to controls (controls = 2.53 +/- 0.10; L-CPA treated = 3.51 +/- 0.31 nmol mg-1 protein, P < 0.01 Student's t tests, n = 6, mean +/- s.e.mean). Biochemical measurements of total NOS activity were made in homogenates of cerebellum 6 h and 48 h following L-CPA administration, times at which L-CPA concentrations are maximal in brain and a time when there is a high proportion of cerebellar granule cell death, respectively. NOS activity as measured by the amount of [3H]-arginine converted to [3H]-citrulline, did not reveal any difference between controls (rats dosed with water) and animals dosed with L-CPA at either 6 or 48 h following dosing. Furthermore the ability of three NOS inhibitors, NG-nitro-L-arginine, 7-bromo-3-nitroindazole and S-methylisothiourea to block the conversion of [3H]-citrulline to [3H]-arginine was identical at 6 and 48 h time points in control and L-CPA treated rats. 3. Quantitative autoradiography using [3H]-NG-nitro-L-arginine was used to measure the relative anatomical distribution and amount of NOS enzyme in the cerebellum of controls and L-CPA-treated rats 48 h following dosing. There was no significant alteration in the binding of [3H]-NG-nitro-L-arginine to granular and molecular layers of the cerebellum of control and L-CPA-treated rat brains. 4. Western blotting using antibodies against the inducible NOS enzyme failed to detect the protein in cerebellums of L-CPA-treated rats when measured 48 h after L-CPA dosing. 5. In conclusion, the increase in cerebellar nitrate/nitrite concentrations in L-CPA-treated rats provides further evidence for activation of NOS in the cerebellum following administration of L-CPA. The failure to demonstrate an increase in NOS activity at 6 or 48 h in L-CPA-treated rats as compared to controls suggests that the source of nitric oxide responsible for the granule cell death must originate from the constitutive NOS enzyme, probably the neuronal form which is highly enriched in the cerebellum. This hypothesis was further substantiated by Western blotting and quantitative autoradiography.

Inhibition of nitric oxide synthesis by NG-nitro-L-arginine methyl ester (L-NAME): requirement for bioactivation to the free acid, NG-nitro-L-arginine

1. The L-arginine derivatives NG-nitro-L-arginine (L-NOARG) and NG-nitro-L-arginine methyl ester (L-NAME) have been widely used to inhibit constitutive NO synthase (NOS) in different biological systems. This work was carried out to investigate whether L-NAME is a direct inhibitor of NOS or requires preceding hydrolytic bioactivation to L-NOARG for inhibition of the enzyme. 2. A bolus of L-NAME and L-NOARG (0.25 micromol) increased coronary perfusion pressure of rat isolated hearts to the same extent (21 +/- 0.8 mmHg; n = 5), but the effect developed more rapidly following addition of L-NOARG than L-NAME (mean half-time: 0.7 vs 4.2 min). The time-dependent onset of the inhibitory effect of L-NAME was paralleled by the appearance of L-NOARG in the coronary effluent. 3. Freshly dissolved L-NAME was a 50 fold less potent inhibitor of purified brain NOS (mean IC50 = 70 microM) than L-NOARG (IC50 = 1.4 microM), but the apparent inhibitory potency of L-NAME approached that of L-NOARG upon prolonged incubation at neutral or alkaline pH. H.p.l.c. analyses revealed that NOS inhibition by L-NAME closely correlated with hydrolysis of the drug to L-NOARG. 4. Freshly dissolved L-NAME contained 2% of L-NOARG and was hydrolyzed with a half-life of 365 +/- 11.2 min in buffer (pH 7.4), 207 +/- 1.7 min in human plasma, and 29 +/- 2.2 min in whole blood (n = 3 in each case). When L-NAME was preincubated in plasma or buffer, inhibition of NOS was proportional to formation of L-NOARG, but in blood the inhibition was much less than expected from the rates of L-NAME hydrolysis. This was explained by accumulation of L-NOARG in blood cells. 5. These results suggest that L-NAME represents a prodrug lacking NOS inhibitory activity unless it is hydrolyzed to L-NOARG. Bioactivation of L-NAME proceeds at moderate rates in physiological buffers, but is markedly accelerated in tissues such as blood or vascular endothelium.

Nitric oxide synthesis inhibition: the effect on rabbit pyloric muscle

The relaxation mechanism of the pyloric smooth muscle is largely dependent on a nonadrenergic noncholinergic (NANC) inhibitory innervation mediated in part by nitric oxide (NO). The aim of the present study was to investigate the effect of NO antagonists on the contractility of the pyloric smooth muscle. In the clinical trial, 10 anesthetized experimental rabbits were infused intraarterially with the NO synthesis inhibitor N-nitro-L-arginine (L-NNA), at a concentration of 10(-4) mol/L; 10 controls received normal saline intraarterially. Pyloric contractility was assessed by balloon manometry. L-NNA infusion produced a dose-dependent increase in the frequency of the pyloric contraction. The maximal increase in frequency occurred during the slow L-NNA infusion rate of 146 ng/min (baseline-adjusted frequencies of experimental v control: 1.267 +/- 0.389 v 0.632 +/- 0.375; P = .001). The increased frequency level was sustained over the subsequent fast infusion rate of 292 ng/min (experimental v control: 1.362 +/- 0.604 v 0.704 +/- 0.579; P = .022). Both the duration and the amplitude of the pyloric contractions were not affected by the L-NNA infusion. These findings suggest that blockage of the L-arginine-NO pathway may have resulted in inhibition of the NANC-induced gastric muscle and relaxation of the pyloric sphincter. The authors speculate that the decreased NO production may be responsible for the sustained contraction of the pyloric smooth muscle with secondary hypertrophy, characteristic of hypertrophic pyloric stenosis.

Regional distribution of binding sites for the nitric oxide synthase inhibitor L-[3H]nitroarginine in rat brain

The regional distribution of NG-nitro-L-[(3)H]arginine (L-[(3)H]NOARG) binding to different regions of rat brain was studied by quantitative autoradiography. These studies revealed highest density of binding sites in cerebellum, anterior olfactory nucleus, islands of Calleja and substantia nigra with appreciable binding site densities in inferior colliculus, superior colliculus, olfactory tubercle and dorsal tegmental nucleus. The regional distribution of L-[(3)H]NOARG binding, is in good agreement with the distribution of nitric oxide synthase studied previously by NADPH-diaphorase staining and immunohistochemistry using antibodies against neuronal nitric oxide synthase. The kinetics of L-[(3)H]NOARG binding to the cytosolic preparations of cerebral cortex, cerebellum, hippocampus and striatum was studied using an in vitro binding technique. Specific L-[(3)H]NOARG binding was of nanomolar affinity, saturable, and best fit to a single-site model in all four brain regions. These studies support the potential use of L-[(3)H]NOARG binding as a tool for further elucidation of the regional distribution and functional properties of NOS in the central nervous system.

Nitro-L-arginine inteferes with the cadmium reduction of nitrate/griess reaction method of measuring nitric oxide production

Nitro-L-arginine is used as an inhibitor of nitric oxide synthase in many biological Systems. Nitric oxide (NO) is unstable and degrades to nitrite NO(2)- and nitrate NO(3)-. The colorimetric reaction of N0(2)- with Griess reagent is commonly used to measure NO(2)-. NO(3)- may be measured as NO(2)- following reduction by cadmium or cadmium/copper. We found that bradykinin increased the formation of NO(2)- by bovine coronary endothelial cells. Nitro-L-arginine further increased the formation of NO(2)-. This increase is due to the interference of nitro-L-arginine in determination of NO(3)- by the cadmium reduction to NO(2)- and Griess reagent reaction. Incubation of nitro-L-arginine with cadmium or cadmium/copper produced a product that reacts with Griess reagent to form a compound that has an absorption spectrum identical to the product formed by NO(2)- and Griess reagent. Caution must be exercised when using the NO(2)-/NO(3)- measurement by the Griess reaction to assess inhibition of nitric oxide synthase by nitro-L-arginine.