Nitric oxide production depends on preceding tetrahydrobiopterin synthesis by endothelial cells: selective suppression of induced nitric oxide production by sepiapterin reductase inhibitors

Sepiapterin reductase: Characteristics and role in diseases

Sepiapterin reductase, a homodimer composed of two subunits, plays an important role in the biosynthesis of tetrahydrobiopterin. Furthermore, sepiapterin reductase exhibits a wide distribution in different tissues and is associated with many diseases, including brain dysfunction, chronic pain, cardiovascular disease and cancer. With regard to drugs targeting sepiapterin reductase, many compounds have been identified and provide potential methods to treat various diseases. However, the underlying mechanism of sepiapterin reductase in many biological processes is unclear. Therefore, this article summarized the structure, distribution and function of sepiapterin reductase, as well as the relationship between sepiapterin reductase and different diseases, with the aim of finding evidence to guide further studies on the molecular mechanisms and the potential clinical value of sepiapterin reductase. In particular, the different effects induced by the depletion of sepiapterin reductase or the inhibition of the enzyme suggest that the non-enzymatic activity of sepiapterin reductase could function in certain biological processes, which also provides a possible direction for sepiapterin reductase research.

Intake of Vitamin K Antagonists and Worsening of Cardiac and Vascular Disease: Results From the Population-Based Gutenberg Health Study

Background Preclinical data have indicated a link between use of vitamin K antagonists ( VKA ) and detrimental effects on vascular structure and function. The objective of the present study was to determine the relationship between VKA intake and different phenotypes of subclinical cardiovascular disease in the population. Methods and Results Clinical and laboratory data, as well as medical-technical examinations were assessed from 15 010 individuals aged 35 to 74 years during a highly standardized 5-hour visit at the study center of the population-based Gutenberg Health Study. In total, the study sample comprised 287 VKA users and 14 564 VKA nonusers. Multivariable analysis revealed an independent association between VKA intake and stiffness index (β=+2.54 m/s; [0.41/4.66]; P=0.019), ankle-brachial index (β=-0.03; [-0.04/-0.01]; P<0.0001), intima-media thickness (β=+0.03 mm [0.01/0.05]; P=0.0098), left ventricular ejection fraction (β=-4.02% [-4.70/-3.33]; P<0.0001), E/E' (β=+0.04 [0.01/0.08]; P=0.014) left ventricular mass (β=+5.34 g/m2.7 [4.26/6.44]; P<0.0001), and humoral markers of cardiac function and inflammation (midregional pro-atrial natriuretic peptide: β=+0.58 pmol/L [0.50/0.65]; P<0.0001; midregional pro-adrenomedullin: β=+0.18 nmol/L [0.14/0.22]; P<0.0001; N-terminal pro B-type natriuretic peptide: β=+1.90 pg/mL [1.63/2.17]; P<0.0001; fibrinogen: β=+143 mg/dL [132/153]; P<0.0001; C-reactive protein: β=+0.31 mg/L [0.20/0.43]; P<0.0001). Sensitivity analysis in the subsample of participants with atrial fibrillation stratified by intake of VKA demonstrated consistent and robust results. Genetic variants in CYP 2C9, CYP 4F2, and VKORC 1 were modulating effects of VKA on subclinical markers of cardiovascular disease. Conclusions These data demonstrate negative effects of VKA on vascular and cardiac phenotypes of subclinical cardiovascular disease, indicating a possible influence on long-term disease development. These findings may be clinically relevant for the provision of individually tailored antithrombotic therapy.

Genetic deletion of CD38 confers post-ischemic myocardial protection through preserved pyridine nucleotides

Following the onset of ischemia/reperfusion (I/R), CD38 activation occurs and is associated with depletion of NAD(P)(H) in the heart as well as myocardial injury and endothelial dysfunction. Studies with pharmacological inhibitors suggest that the NADP+-hydrolyzing ability of CD38 can deplete the NAD(P)(H) pools. However, there is a need for more specific studies on the importance of CD38 and its role in the process of endothelial dysfunction and myocardial injury in the post-ischemic heart. Therefore, experiments were performed in hearts of mice with global gene knockout of CD38. Isolated perfused CD38-/- and wild type (WT) mouse hearts were studied to determine the link between CD38 activation, the levels of NADP(H), endothelial dysfunction, and myocardial injury after I/R. Genetic deletion of CD38 preserves the myocardial and endothelial NADP(H) pools compared to WT. Whole heart BH4 levels in CD38-/- hearts were also preserved. Post-ischemic levels of cGMP were greatly depleted in WT hearts, but preserved to near baseline levels in CD38-/- hearts. The preservation of these metabolite pools in CD38-/- hearts was accompanied by near full recovery of NOS-dependent coronary flow, while in WT hearts, severe impairment of endothelial function and NOS uncoupling occurred with decreased NO and enhanced superoxide generation. CD38-/- hearts also exhibited marked protection against I/R with preserved glutathione levels, increased recovery of left ventricular contractile function, decreased myocyte enzyme release, and decreased infarct size. Thus, CD38 activation causes post-ischemic depletion of NADP(H) within the heart, with severe depletion from the endothelium, resulting in endothelial dysfunction and myocardial injury.

Lipopolysaccharide enhances interferon-γ-induced nitric oxide (NO) production in murine vascular endothelial cells via augmentation of interferon regulatory factor-1 activation

Lipopolysaccharide (LPS) enhances the production of nitric oxide (NO) in interferon (IFN)-γstimulated vascular endothelial cells. We studied the mechanism by which LPS enhances IFN-γ-induced NO production by using the murine vascular endothelial cell line, END-D. LPS enhanced IFN-γinduced NO production via augmented expression of inducible type NO synthase (iNOS) mRNA. LPS significantly augmented the activation of interferon regulatory factor (IRF)-1 in IFN-γ-stimulated END-D cells, although it did not affect the activation of either MyD88-dependent nuclear factor (NF)-κB or MyD88-independent IRF-3. SB203580, an inhibitor of p38 mitogen-activated protein kinase (MAPK), prevented the nuclear translocation of IRF-1 in LPS and IFN-γ-stimulated END-D cells, and inhibited the iNOS expression and NO production in those cells. Therefore, it is proposed that LPS enhanced NO production in IFN-γ-stimulated END-D cells via augmenting p38 MAPKmediated IRF-1 activation.

Type 2 Diabetes: Endothelial dysfunction and Exercise

PURPOSE

Vascular endothelial dysfunction is an early marker of atherosclerosis characterized by decreased nitric oxide bioavailability in the vascular endothelium and smooth muscle cells. Recently, some animal models and in vitro trials demonstrated that excessive superoxide production from mitochondria within vascular endothelial cells played a role in the pathogenesis of atherosclerosis in type 2 diabetes. This review provides a systematic assessment of the effectiveness of exercise to identify effective approaches to recognize diabetes risk and prevent progression to heart disease.

METHODS

A systematic literature search was conducted to retrieve articles from 1979 to 2013 using the following databases: the MEDLINE, PubMed. Articles had to describe an intervention that physical activity and exercise to identify effective approaches to heart and vascular endothelium.

RESULTS

Currently, physical activity and exercise guidelines aimed to improve cardiovascular health in patients with type 2 diabetes are nonspecific. Benefit of aerobic exercise training on vascular endothelial function in type 2 diabetic patients is still controversial.

CONCLUSION

it is necessary to demonstrate the mechanism of endothelial dysfunction from live human tissues so that we can provide more specific exercise training regimens to enhance cardiovascular health in type 2 diabetic patients.

The regulation of vascular tetrahydrobiopterin bioavailability

6R l-erythro-5,6,7,8-tetrahydrobiopterin (BH4) is an essential cofactor for several enzymes including phenylalanine hydroxylase and the nitric oxide synthases (NOS). Oral supplementation of BH4 has been successfully employed to treat subsets of patients with hyperphenylalaninaemia. More recently, research efforts have focussed on understanding whether BH4 supplementation may also be efficacious in cardiovascular disorders that are underpinned by reduced nitric oxide bioavailability. Whilst numerous preclinical and clinical studies have demonstrated a positive association between enhanced BH4 and vascular function, the efficacy of orally administered BH4 in human cardiovascular disease remains unclear. Furthermore, interventions that limit BH4 bioavailability may provide benefit in diseases where nitric oxide over production contributes to pathology. This review describes the pathways involved in BH4 bio-regulation and discusses other endogenous mechanisms that could be harnessed therapeutically to manipulate vascular BH4 levels.

Over-expression of GTP-cyclohydrolase 1 feedback regulatory protein attenuates LPS and cytokine-stimulated nitric oxide production

GTP-cyclohydrolase 1 (GTP-CH1) catalyses the first and rate-limiting step for the de novo production of tetrahydrobiopterin (BH(4)), an essential cofactor for nitric oxide synthase (NOS). The GTP-CH1-BH(4) pathway is emerging as an important regulator in a number of pathologies associated with over-production of nitric oxide (NO) and hence a more detailed understanding of this pathway may lead to novel therapeutic targets for the treatment of certain vascular diseases. GTP-CH1 activity can be inhibited by BH(4) through its protein-protein interactions with GTP-CH1 regulatory protein (GFRP), and transcriptional and post-translational modification of both GTP-CH1 and GFRP have been reported in response to proinflammatory stimuli. However, the functional significance of GFRP/GTP-CH1 interactions on NO pathways has not yet been demonstrated. We aimed to investigate whether over-expression of GFRP could affect NO production in living cells. Over-expression of N-terminally Myc-tagged recombinant human GFRP in the murine endothelial cell line sEnd 1 resulted in no significant effect on basal BH(4) nor NO levels but significantly attenuated the rise in BH(4) and NO observed following lipopolysaccharide and cytokine stimulation of cells. This study demonstrates that GFRP can play a direct regulatory role in iNOS-mediated NO synthesis and suggests that the allosteric regulation of GTP-CH1 activity by GFRP may be an important mechanism regulating BH(4) and NO levels in vivo.

Analysis of the effect of tetrahydrobiopterin on PAH gene expression in hepatoma cells

Tetrahydrobiopterin (BH4)-responsive phenylalanine hydroxylase (PAH) deficiency is a recently recognized variant of phenylketonuria, with a probable multifactorial molecular basis. In this study we have investigated the effect of BH4 on PAH gene expression in human hepatoma. Our results show that increased BH4 levels result in an enhancement of PAH activity and PAH protein, due to longer turnover rates, while PAH mRNA levels remain unchanged. This was confirmed for mutant PAH proteins (A309V, V388M and Y414C) associated to in vivo BH4 responsiveness, validating previous studies. We can conclude that there is no effect of the cofactor on PAH gene transcription, probably being the chemical chaperone effect of BH4 stabilizing mutant PAH proteins the major underlying mechanism of the response.

Effect of Low-Intensity Acenocoumarol on Frequency and Severity of Migraine Attacks

OBJECTIVE

To investigate the effect of low-intensity acenocoumarol treatment (target INR 1.5 to 2.0) on the frequency and severity of migraine attacks.

BACKGROUND

The positive effect of anticoagulation on migraine has been described in case reports and observational studies.

METHODS

We conducted a randomized, open, crossover study in migraine patients. After a run-in period of 8 weeks, all patients received acenocoumarol or propranolol during a period of 12 weeks and, after a washout period of 2 weeks, propranolol or acenocoumarol during a second period of 12 weeks.

RESULTS

Nineteen patients fulfilling the criteria were included. In 12 patients with complete data collection, only one good responder could be noted. In the other patients, treatment with low-intensity acenocoumarol did not show improvement of migraine symptoms compared with the run-in period. Treatment with propranolol showed a trend towards improvement compared with the run-in period. No serious adverse events were observed.

CONCLUSIONS

Overall, low-intensity acenocoumarol treatment has no prophylactic effect in migraine patients.

Role of tetrahydrobiopterin in adrenocorticotropic hormone-induced hypertension in the rat

Adrenocorticotropic hormone (ACTH)-induced hypertension in the rat is characterized by nitric oxide deficiency. Tetrahydrobiopterin (BH4) is an essential cofactor for the enzyme nitric oxide synthase and glucocorticoids have been reported to reduce cytokine-induced BH4 production. Accordingly we hypothesized that ACTH-induced hypertension would be reversed by BH4 supplementation. Male Sprague-Dawley rats (n = 33) were treated with BH4 in vehicle (10 mg/kg/day i.p.) or vehicle alone (5 mg/kg/day i.p. of ascorbic acid in 4 mM HCl) for 10 days. ACTH (0.2 mg/kg s.c.) or saline daily injection was started 2 days after BH4 or vehicle treatment and continued for 8 days. Systolic blood pressure (SBP) was measured on alternate days using the tail cuff method. Treatment with HCl, ascorbic acid or BH4 alone had no effect on SBP. In saline treated rats, neither BH4 nor its vehicle modified SBP. In ACTH treated rats, SBP was increased in both BH4 (from 128 +/- 6 to 142 +/- 4 mmHg, T0 to T10, P < 0.0005, one way ANOVA) and vehicle groups (from 127 +/- 3 to 158 +/- 7 mmHg, T0 to T10, P < 0.001, one way ANOVA). There was no significant difference in SBP between BH4 + ACTH treated and vehicle + ACTH treated rats. Thus, daily injection of BH4 (10 mg/kg i.p.) failed to prevent the development of ACTH-induced hypertension in rat.

Bacterial translocation up-regulates GTP-cyclohydrolase I in mesenteric vasculature of cirrhotic rats

In cirrhosis, arterial vasodilation and the associated hemodynamic disturbances are most prominent in the mesenteric circulation, and its severity has been linked to bacterial translocation (BT) and endotoxemia. Synthesis of nitric oxide (NO), the main vasodilator implicated, is dependent on the essential cofactor tetrahydrobiopterin (BH(4)). The key enzyme involved in BH(4) synthesis is GTP-cyclohydrolase I (GTPCH-I), which is stimulated by endotoxin. Therefore, we investigated GTPCH-I activity and BH(4) biosynthesis in the mesenteric vasculature of cirrhotic rats with ascites, as well as their relationship with BT and endotoxemia, serum NO, and mean arterial pressure (MAP). GTPCH-I activity and BH(4) content in mesenteric vasculature was determined by high-performance liquid chromatography. BT was assessed by standard bacteriologic culture of mesenteric lymph nodes (MLNs). Serum endotoxin was measured by a kinetic turbidimetric limulus amebocyte lysate assay, and serum NO metabolite (NOx) concentrations were assessed by chemiluminescence. BT was associated with local lymphatic and systemic appearance of endotoxin and was accompanied by increases in serum NOx levels. GTPCH-I activity and BH(4) content in mesenteric vasculature were both increased in animals with BT and correlated significantly (r = 0.69, P <.01). Both GTPCH-I activity and BH(4) levels significantly correlated with serum endotoxin and NOx levels (r = 0.69 and 0.54, 0.81 and 0.53, P <.05). MAP (a marker of systemic vasodilatation) correlated with endotoxemia (r = 0.58, P <.03) and with GTPCH-I activity (r = 0.69, P <.01). In conclusion, in cirrhotic animals BT appears to lead to endotoxemia, stimulation of GTPCH-I, increased BH(4) synthesis, and further enhancement of vascular NO production that leads to aggravation of vasodilatation.

The role of nitric oxide in vascular headache

Shortly after the invention of nitroglycerin (NTG), it was noticed that this substance is capable of inducing a violent headache. Only recently, it became known that this was due to the release of nitric oxide (NO) by NTG. As the molecular mechanism of migraine pain remains to be determined, NTG, being pro-drug for NO, has been used to study the aetiology and pathophysiology of migraine. Such studies with NTG- and also histamine-induced headaches, have led to propose that NO may be the causative molecule in migraine pain. The evidence supporting the role of NO in migraine is discussed, e.g. substances capable of inducing experimental vascular headache do so with NO as the common mediator, while drugs with antimigraine activity inhibit NO and the cascade of intracellular reactions triggered by NO. The importance of NO as a potential initiator of the migraine attack opens new directions for the pharmacological treatment of migraine and other vascular headaches.

Mechanism of systemically injected interferon-alpha impeding monoamine biosynthesis in rats: role of nitric oxide as a signal crossing the blood-brain barrier

The serious and characteristic side effects of interferon-alpha (IFN-alpha) therapy on the central nervous system, resulting in such problems as affective disorders or parkinsonism, have led us to investigate the biochemical mechanism of the effects of IFN-alpha on the monoaminergic neurotransmitter system using an animal model (rats). We first examined the concentrations of tetrahydrobiopterin (BH(4)) and monoamines in several regions of the brain after the intramuscular injection of IFN-alpha into rats; the levels of BH(4) and dopamine significantly decreased in the amygdala and raphe areas as compared with those of the controls. Based on these results, we further examined the concentrations of BH(4) and nitrite (NO(2)(-)) plus nitrate (NO(3)(-)), metabolites of nitric oxide (NO), in the amygdala and raphe areas after the intramuscular injection of IFN-alpha; the concentrations of both BH(4) and NO(2)(-)+NO(3)(-) significantly decreased as compared with the control. Furthermore, the addition of N(G)-monomethyl L-arginine, an inhibitor of NO synthase, after the injection of IFN-alpha restored the decreased levels of both NO(2)(-)+NO(3)(-) and BH(4) to control levels. As a result, nitric oxide induced by the intramuscular injection of IFN-alpha was found to cross the blood-brain barrier and suppress both tetrahydrobiopterin biosynthesis and dopamine production in the amygdala and raphe areas.

The antithyroid agent 6-n-propyl-2-thiouracil is a mechanism-based inactivator of the neuronal nitric oxide synthase isoform

6-n-Propyl-2-thiouracil (6-PTU), the antithyroid agent, produces a time-, concentration-, and turnover-dependent inactivation of the NO synthetic capability of the neuronal nitric oxide synthase isoform irreversible by either arginine or (6R)-5,6,7,8-tetrahydro-L-biopterin. By contrast 6-PTU produces an inhibition of the cytokine-inducible and endothelial nitric oxide synthases fully reversible by arginine. The inactivation of neuronal nitric oxide synthase by 6-PTU follows first order kinetics, and is inhibited competitively by both arginine and (6R)-5,6,7,8-tetrahydro-L-biopterin, but is not accompanied by either a loss of heme-CO binding, heme fluorescence, or disassembly of dimeric structure. 2-Thiouracil behaves qualitatively identically to 6-PTU. Turnover-dependent inactivation of neuronal nitric oxide synthase by [2-14C]-2-thiouracil is accompanied by incorporation of radioactivity into the polypeptide chain. Ca2+-dependent NO formation by GH3 pituitary cells is inhibited by 6-PTU in a manner enhanced by depletion of either extracellular arginine or intracellular (6R)-5,6,7,8-tetrahydro-L-biopterin. These observations establish that 6-PTU is an alternate substrate, mechanism-based inactivator of the neuronal nitric oxide synthase isoform with the ability to suppress cellular NO formation.

The nitric oxide system in glucocorticoid-induced hypertension

The blood pressure-raising effects of adrenocortical steroids with predominantly glucocorticoid activity, both naturally occurring and synthetic, are well known. Recent evidence suggests that the nitric oxide system plays a key role in the hypertension produced by glucocorticoids. Glucocorticoid actions at various sites in the nitric oxide synthase (NOS) pathway may result in elevated blood pressure. These include: alterations in l-arginine availability or transport; NOS2 and NOS3 downregulation; reduced cofactor bioavailability; NOS uncoupling; a concomitant elevation in reactive oxygen species and removal of nitric oxide (NO) from the vascular environment; alterations in whole body antioxidant status; and erythropoietin induced resistance to NO.

Augmentation of nitric oxide production by gamma interferon in a mouse vascular endothelial cell line and its modulation by tumor necrosis factor alpha and lipopolysaccharide

The effect of gamma interferon (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), and lipopolysaccharide (LPS) on nitric oxide (NO) production in the mouse vascular aortic endothelial cell line END-D was examined. LPS, TNF-alpha, and a low concentration of IFN-gamma inhibited NO production in END-D cells, while a high concentration of IFN-gamma definitely enhanced it. The NO production induced by a high concentration of IFN-gamma was further augmented by using IFN-gamma in combination with LPS or TNF-alpha. In sequential incubations of LPS and IFN-gamma, the enhancement of NO production required prior treatment with IFN-gamma. Stimulation of END-D cells with a high concentration of IFN-gamma led to the expression of inducible NO synthase (iNOS). The augmentation of NO production by IFN-gamma alone or in combination with LPS or TNF-alpha was completely blocked by several inhibitors of iNOS. It was strongly suggested that a high concentration of IFN-gamma itself enhanced NO production in END-D cells through inducing the expression of iNOS. LPS and TNF-alpha exclusively modulated the activity of iNOS once its expression was triggered by IFN-gamma. On the other hand, a low concentration of IFN-gamma, LPS, and TNF-alpha reduced NO production through down-regulating constitutive NOS (cNOS). The differential regulation of cNOS- and iNOS-mediated NO production by IFN-gamma, TNF-alpha, and LPS is discussed.

Structure, chromosomal localization, and expression of the Drosophila melanogaster gene encoding sepiapterin reductase

We have isolated and characterized a Drosophila melanogaster gene encoding the sepiapterin reductase (SR). The gene does not have introns. The 5'- and 3'-RACE analysis, which determined the transcription start point (tsp) and polyadenylation site, respectively, showed that the gene produces single mRNA species. The potential promoter region lacks distinct TATAAA or CCAAT box consensus sequences. RNA blot analysis revealed that the gene encodes a 1.4kb transcript that could be detected throughout development and in both heads and bodies of adults. The Drosophila SR gene maps to 15A on the X chromosome.

Patients with acenocoumarol treatment and migraine

OBJECTIVE

The aim of our study was to investigate the possible effect of acenocoumarol, which is indicated for nonneurological disease, on headache.

BACKGROUND

It has been suggested that anticoagulation can have beneficial effects in the control of migraine attacks.

METHODS

Four hundred randomized patients on oral anticoagulant therapy were asked to complete a questionnaire regarding their headaches.

RESULTS

Headache was present before or during oral anticoagulation in 166 (66 migraineurs and 100 nonmigraineurs) of 326 respondents. The major finding was that oral anticoagulation produced improvement in 63% of patients with migraine versus 38% of patients with nonmigranous headache. Improvement was related to the severity of migraine but not to age.

CONCLUSIONS

Oral anticoagulant therapy can improve migraine. The way in which anticoagulant therapy acts on migraine is unknown, but potential mechanisms include its effect on platelet aggregability and pharmacological effects such as suppression of enhanced nitric oxide.

Isolation and characterization of the Drosophila melanogaster cDNA encoding the sepiapterin reductase

We have isolated and characterized the cDNA encoding Drosophila melanogaster sepiapterin reductase (SR). The amino acid sequence deduced from the cDNA sequence was 29% identical to those of mammalian SRs. The active site residues proposed from the three-dimensional structure of mouse SR are well conserved in Drosophila SR. The protein-coding region of the cDNA was expressed in Escherichia coli as a histidine fusion protein, and the resulting recombinant protein proved to have SR activity. The SR activity of the recombinant protein was inhibited by two indoleamines, N-acetyl serotonin and melatonin. Southern analysis suggests that the Drosophila SR gene is encoded by a single copy gene. RNA blot analysis revealed that the gene expresses 1.5 kb mRNA in both adult heads and bodies.

Genomic organization and chromosomal localization of the human sepiapterin reductase gene

Sepiapterin reductase (SPR) catalyzes the final step of the biosynthetic pathway of tetrahydrobiopterin, which is an essential cofactor for aromatic amino acid hydroxylases and nitric oxide synthases. To aid the analysis of any possible human diseases caused by mutations in SPR, we have cloned and characterized the human SPR gene. The gene is composed of three exons spanning approximately 4 kilobases. The transcriptional starting point was determined around the cytosine nucleotide at position -81 by primer extension and RT-PCR analyses. There was no typical TATA-box within 300 bp from the transcriptional starting point. We found the Sp1-binding consensus sequence in the 5'-flanking region. The human SPR gene was mapped to chromosome band 2p13 by fluorescence in situ hybridization.

The regulation of dopamine release from striatum slices by tetrahydrobiopterin and L-arginine-derived nitric oxide

The regulation of dopamine release by 6(R)-tetrahydrobiopterin (BH4) and l-arginine-derived nitric oxide was examined by using a method of superfusion of rat striatum slices in vitro. l-Arginine, which can produce nitric oxide (NO) through the action of NO synthase, induces a concentration-dependent increase of [3H] dopamine release in the superfusate of striatum slices. Pretreatment with inhibitors of NO synthase or with inhibitors of BH4 synthesis diminishes the increase of [3H] dopamine release mediated by arginine. This increase is almost completely restored following repletion of intracellular BH4 levels by incubation of the slices with 7, 8-dihydrobiopterin. Adding exogenous BH4 directly to the superfusion fluid leads to a massive increase in [3H] dopamine release which can be inhibited 75% by superoxide dismutase and catalase, but is not inhibited by NG-nitro-arginine, a NO synthase inhibitor, or alpha-methyl-p-tyrosine, a tyrosine hydroxylase inhibitor. The increase of intracellular BH4 concentration by dihydrobiopterin administration causes a small increase of dopamine release which can be partially diminished by NG-nitro-arginine or alpha-methyl-p-tyrosine. It is suggested that the increase of dopamine release stimulated by an enhancement of intracellular BH4 is dependent on its cofactor activity with NO synthase and tyrosine hydroxylase. This study has also demonstrated that BH4 is a regulator of NO-mediated dopamine release in the striatum. Published by Elsevier Science B.V.

Reduction by tetrahydrobiopterin of H2O2-induced endothelial cell injury

The purpose of this study was to examine the effect of tetrahydrobiopterin, a co-factor of nitric oxide synthase, on H2O2-induced endothelial cell injury. Pretreatment with sepiapterin, a precursor of tetrahydrobiopterin biosynthesis, increased tetrahydrobiopterin content of endothelial cells, and reduced H2O2-induced endothelial cell injury, which was measured by leakage of lactate dehydrogenase. Both the increase in tetrahydrobiopterin content and the protective effect of sepiapterin were prevented by co-pretreatment with N-acetylserotonin, an inhibitor of sepiapterin reductase. Although Ca2+ ionophore ionomycin-induced nitric oxide synthesis was increased by pretreatment with sepiapterin, the protective effect of sepiapterin was not affected by an inhibitor of nitric oxide synthesis. On the other hand, pretreatment with sepiapterin also reduced H2O2-induced rat foetal lung fibroblast cell injury via an increase in tetrahydrobiopterin content, despite rat foetal lung fibroblast cells lacking nitric oxide synthase. Moreover, increase in tetrahydrobiopterin strongly reduced H2O2-induced intracellular oxidative stress. These findings indicate that sepiapterin reduces H2O2-induced endothelial cell injury via an increase in tetrahydrobiopterin content. Although increase in endothelial tetrahydrobiopterin content stimulated nitric oxide production, the protective effect of tetrahydrobiopterin against H2O2-induced endothelial cell injury is unlikely to be related to the stimulation of nitric oxide release from nitric oxide synthase. The protective effect of tetrahydrobiopterin may involve reactive oxygen species-scavenging activity.

Modulation of inducible nitric oxide synthase mRNA stability by tetrahydrobiopterin in vascular smooth muscle cells

Tetrahydrobiopterin (BH4) regulates inducible nitric oxide synthase (iNOS) as cofactor and allosteric effector. The present paper describes a novel function of BH4 in vascular smooth muscle cells (SMC). By varying BH4 levels with dicumarol (an inhibitor of BH4 synthesis) and sepiapterin (an exogenous source of co-factor), we investigated iNOS expression in activated rat aortic SMC. In sepiapterin-supplemented cells, iNOS protein levels were increased while in dicumarol-treated cells, iNOS levels were diminished. Time-kinetic experiments revealed that inhibition or supplementation of BH4 synthesis had no effects on iNOS induction or transcription rate. However, iNOS mRNA was present over a prolonged time in sepiapterin-supplemented SMC. Analysis of iNOS mRNA levels showed stable iNOS mRNA in sepiapterin-treated cells 8 hours after transcription inhibition, while in dicumarol-treated cells iNOS mRNA disappeared. The decrease of iNOS mRNA by dicumarol was abolished by sepiapterin. These data indicate that BH4 post-transcriptionally stabilizes iNOS mRNA in SMC. By this way BH4 modulates iNOS expression in the vascular system.

Protective effects of tetrahydrobiopterin against nitric oxide-induced endothelial cell death

The purpose of this study was to examine whether tetrahydrobiopterin (BH4), one of the cofactors of nitric oxide (NO) synthase, attenuates NO-induced endothelial cell death. S-Nitroso-N-acetyl-DL-penicillamine (SNAP) was used as a NO donor. Endothelial cell death was assessed by the leakage of intracellular lactate dehydrogenase (LDH). Addition of SNAP to endothelial cells time- and concentration-dependently induced endothelial cell death. The SNAP-induced endothelial cell death was strongly reduced by the treatment with carboxy-PTIO, a NO scavenger, or catalase, but not with superoxide dismutase (SOD). Moreover, pretreatment with sepiapterin, a precursor of BH4, increased intracellular BH4 content, and strongly reduced the SNAP-induced endothelial cell death. Both the increase in BH4 content and the protective effects of sepiapterin were prevented by co-pretreatment with N-acetylserotonin (NAS), an inhibitor of BH4 synthesis. These findings suggest that the cytotoxicity of NO released from SNAP involves H2O2 production, and increase in intracellular BH4 content attenuates NO-induced endothelial cell death. Scavenging of H2O2 by BH4 may be at least one of the mechanisms by which BH4 reduces NO-induced endothelial cell death.

Decrease in the concentrations of transforming growth factor-beta 1 in the sera of patients with Kawasaki disease

Kawasaki disease (KD) is one of the most important forms of vasculitis, and is characterized by the initiation of a proinflammatory cytokine cascade. To further characterize the immunological profile of KD, we measured the serum levels of transforming growth factor-beta 1 (TGF-beta 1) as a regulatory cytokine. We determined the concentration of TGF-beta 1 in the sera of the patients with KD, anaphylactoid purpura (AP), and scarlet fever, using a sandwich enzyme linked immunosorbent assay. The serum levels of TGF-beta 1 were decreased in patients with KD, but not in patients with AP or scarlet fever during the acute stage. We found an inverse correlation between TGF-beta 1 and soluble tumor necrosis factor (TNF) receptor levels in KD patients during the acute and subacute stage. Decreased levels of TGF-beta 1, in particular to suppress TNF alpha (TNF-alpha) production, is an important part of the regulatory system of increased TNF-alpha production which cause vasculitis.

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.

Tetrahydrobiopterin synthesis precedes nitric oxide-dependent inhibition of insulin secretion in INS-1 rat pancreatic beta-cells

Interleukin 1 (IL-1) induces pancreatic beta-cell dysfunction mainly due to overproduction of nitric oxide (NO). Since tetrahydrobiopterin (BH4) is a obligatory cofactor of NO synthases, we examined the temporal relationship of BH4 synthesis, NO production and insulin secretion in a pancreatic beta-cell line (INS-1) which was exposed to IL-1. IL-1 affected BH4 synthesis in a time- and concentration-dependent manner. At a concentration of 10 ng/ml IL-1 caused an increase in intracellular BH4 with peak levels being observed at 6 hours followed by a steady decline in the cellular BH4 content. The increase in BH4 synthesis was followed by enhanced NO production and, consecutively, inhibition of insulin secretion. The concentration-dependent regulation of BH4 synthesis, NO production and suppression of insulin secretion indicate a functional link between these parameters in pancreatic beta-cells.

Tetrahydrobiopterin, a cofactor for nitric oxide synthase, produces endothelium-dependent dilation of mouse pial arterioles

BACKGROUND AND PURPOSE

Tetrahydrobiopterin (THBP) is an essential cofactor for nitric oxide synthase (NOS), which is responsible for the synthesis of the endothelium-derived relaxing factor (EDRF) responsible for mediating the vasorelaxation produced by acetylcholine (ACh). Previous publications suggest that EDRFACh is continuously synthesized and released from the endothelium of mouse pial arterioles. If so, then one may predict that addition of THBP will increase the local production of EDRFACh and produce an endothelium-dependent relaxation that can be blocked by application of a known inhibitor of NOS. This study tests the prediction.

METHODS

The pial vessels were observed at a continuously suffused craniotomy site by means of intravital television microscopy. The effects of topically applied THBP on diameter were monitored before and after endothelial damage and before and after local treatment with the NOS inhibitor N-guanidino-L-monomethyl arginine (LNMMA). The endothelial damage was produced by a helium-neon laser in the presence of Evans blue dye.

RESULTS

A dose-dependent relaxation was produced by 10(-3) and 10(-2) mol/L THBP. The response was virtually eliminated by endothelial injury. LNMMA 10(-6) mol/L also greatly inhibited dilation.

CONCLUSIONS

The data are consistent with all reports that THBP is a cofactor for constitutive endothelial NOS. The data are consonant with previous results suggesting that EDRFACh is continually synthesized and released. It appears that THBP increases this synthesis and consequently the local level of released EDRFACh. The continuous spontaneous synthesis/release of EDRFACh modulates basal tone and, according to other studies, helps maintain a platelet-free endothelial surface.

Effect of septicaemia on the plasma levels of biopterin and nitric oxide metabolites in rats and rabbits

Live Escherichia coli decreased mean arterial blood pressure in rabbits from 67 to 20 mmHg. E. coli did not affect blood pressure in rats but did significantly increase heart rate by 29%. To related the cardiovascular effects with putative relevant biochemical pathways, the plasma levels of nitrate + nitrite (NOx) and biopterin, representing the main metabolites of nitric oxide and tetrahydrobiopterin, respectively, were determined in conscious rats and rabbits after treatment with live E. coli. In rats, E. coli induced a rapid 43% increase in the plasma level of biopterin preceding the 7- to 26-fold increase in NOx level. In rabbits, no increase in the NOx level was observed despite a 3- to 5-fold increase in the biopterin level at 6-10 hr posttreatment. It is concluded that the synthesis of tetrahydrobiopterin precedes nitric oxide synthesis after induction of septicaemia in the rat. After the induction of septicaemia, rabbits show a clear hypotensive response and an increase in biopterin level but no concomitant increase in NOx. Biopterin apparently represents a more appropriate biochemical marker of septic shock than does NOx.

Role of tetrahydrobiopterin availability in the regulation of nitric-oxide synthase expression in human mesangial cells

Human mesangial cells express an inducible form of nitric-oxide synthase (iNOS) after treatment with cytokines. Tetrahydrobiopterin (BH4), an essential cofactor for NOS, is required for cytokine-induced NO generation. We report here that BH4 is necessary not only for the activity but also for the expression of iNOS in human mesangial cells. Inhibition of de novo BH4 synthesis with 2,4-diamino-6-hydroxypyrimidine (DAHP) significantly attenuated iNOS activity as well as mRNA and protein expression in response to interleukin 1beta plus tumor necrosis factor alpha (IL-1beta/TNF-alpha). In contrast, sepiapterin, which provides BH4 through the pterin salvage pathway, strongly potentiated IL-1beta/TNF-alpha-induced iNOS expression and abrogated the inhibitory effect of DAHP. Inhibition of the pterin salvage pathway with methotrexate abolished sepiapterin potentiation of iNOS induction but did not alter the effect of IL-1beta/TNF-alpha. Determination of intracellular pteridines confirmed that sepiapterin markedly raised BH4 content, an effect that was blocked by methotrexate. These results suggest that BH4 availability plays an important role in the regulation of iNOS expression. The effect of BH4 appears to be mediated, at least in part, by an increase in mRNA stability, as indicated by the observation that DAHP shortened, whereas sepiapterin prolonged the half-life of IL-1beta/TNF-alpha-induced iNOS mRNA. Taken together, our results suggest that the biosynthesis of BH4 contributes to cytokine induction of iNOS expression in human mesangial cells through the stabilization of iNOS mRNA.

Selective pharmacological inhibition of distinct nitric oxide synthase isoforms

Nitric oxide (NO) is produced in physiological and pathophysiological conditions by three distinct isoforms of NO synthase (NOS): endothelial NOS (ecNOS), inducible NOS (iNOS), and brain NOS (bNOS). Selective inhibition of iNOS may be beneficial in various forms of shock and inflammation, whereas inhibition of bNOS may protect against neuroinjury. This article surveys the enzymatic mechanism of NO production, lists the strategies and pharmacological tools for selective inhibition of distinct NOS isoforms, and considers the side-effects of the various approaches. Selective inhibition of NOS isoforms is achieved by: (a) targeting the differential co-factor (calmodulin or tetrahydrobiopterin) requirement of various NOS isoforms, and NOS; (b) targeting the differential substrate requirements of cells expressing various isoforms of NOS (L-arginine uptake blockers or arginase); (c) the use of pharmacological agents that are selectively taken up by cells expressing various isoforms of NOS (7-nitroindazole); or (d) developing pharmacological NOS inhibitors with isoform specificity. The amino acid-based NOS inhibitor, NG-nitro-L-arginine, shows a preference for ecNOS and bNOS over iNOS, whereas L-N6-(1-iminoethyl)lysine is selective for iNOS over bNOS. Certain non-amino acid-based small molecules, such as aminoguanidine and certain S-alkylated isothioureas, also express selectivity towards iNOS and have anti-inflammatory and anti-shock properties. 7-nitroindazole, a bNOS-selective inhibitor, protects in central nervous system injury. Clearly, there are a number of distinct approaches that are worthy of further research efforts in order to achieve even more selective targeting of various NOS isoforms

Alcohol and the brain: what's NO got to do with it?

A potential role for nitric oxide in alcohol-induced changes in brain function is discussed. Chronic alcohol exposure may lead to excitotoxicity partially due to increased levels of nitric oxide (NO). Excessive NO has been linked to cytotoxicity in neurons, glia and myelin. Cytokines produced in response to cell injury may trigger increased production of NO. These events may be involved in alcohol-induced brain damage. Formation of NO has recently been linked to increased preference for and tolerance to alcohol. A hypothesis for prevention and treatment of alcohol-induced brain damage, and craving and alcohol intake by alcoholics is proposed.

Regulation of staphylococcal enterotoxin B-elicited nitric oxide production by endothelial cells

The effect of staphylococcal enterotoxin B (SEB)-elicited inducible nitric oxide synthase (iNOS) in mouse endothelial cells was investigated. Results showed that SEB stimulated the same level of NO production in gamma interferon (IFN-gamma)-primed cells as did trichloroacetic acid-extracted lipopolysaccharide. The kinetics of induced NO production and expression of mRNA for iNOS differed markedly in endothelial and macrophage cells. Induced endothelial nitrite production was transient and was 15 to 20% of that generated by macrophage cells; mRNA levels peaked by 2 h and then steadily declined, whereas macrophage message levels continually increased. The ability of endothelial cells to produce SEB-induced NO depended on priming with IFN-gamma, although detectable mRNA could be elicited by SEB alone. Induction of endothelial iNOS mRNA was inhibited by cycloheximide, which indicated a requirement for de novo protein synthesis. Niacinamide and interleukin-10 significantly reduced SEB-induced endothelial NO production. Both are reported to affect IFN-gamma-induced class II major histocompatibility complex (MHC) expression on antigen-presenting cells. Niacinamide reduced iNOS mRNA levels and markedly reduced IFN-gamma induction of endothelial class II MHC surface antigen. Interleukin-10 did not consistently reduce iNOS mRNA expression and had no effect on IFN-gamma induction of endothelial class II MHC surface antigen. These results suggest that SEB interacts with IFN-gamma-primed endothelial cells to elicit induced NO and that this induction can be effectively modulated at the receptor or transcriptional level.