Tetrahydrobiopterin analogues with NO-dependent pulmonary vasodilator properties

Reduced NO levels due to the deficiency of tetrahydrobiopterin (BH(4)) contribute to impaired vasodilation in pulmonary hypertension. Due to the chemically unstable nature of BH(4), it was hypothesised that oxidatively stable analogues of BH(4) would be able to support NO synthesis to improve endothelial dysfunction in pulmonary hypertension. Two analogues of BH(4), namely 6-hydroxymethyl pterin (HMP) and 6-acetyl-7,7-dimethyl-7,8-dihydropterin (ADDP), were evaluated for vasodilator activity on precontracted rat pulmonary artery rings. ADDP was administered to pulmonary hypertensive rats, followed by measurement of pulmonary vascular resistance in perfused lungs and eNOS expression by immunohistochemistry. ADDP and HMP caused significant relaxation in vitro in rat pulmonary arteries depleted of BH(4) with a maximum relaxation at 0.3μM (both P<0.05). Vasodilator activity of ADDP and HMP was completely abolished following preincubation with the NO synthase inhibitor, L-NAME. ADDP and HMP did not alter relaxation induced by carbachol or spermine NONOate. BH(4) itself did not produce relaxation. In rats receiving ADDP 14.1mg/kg/day, pulmonary vasodilation induced by calcium ionophore A23187 was augmented and eNOS immunoreactivity was increased. In conclusion, ADDP and HMP are two analogues of BH(4), which can act as oxidatively stable alternatives to BH(4) in causing NO-mediated vasorelaxation. Chronic treatment with ADDP resulted in improvement of NO-mediated pulmonary artery dilation and enhanced expression of eNOS in the pulmonary vascular endothelium. Chemically stable analogues of BH(4) may be able to limit endothelial dysfunction in the pulmonary vasculature.

Development of a quantitative RT-PCR assay to examine the kinetics of ribosome depurination by ribosome inactivating proteins using Saccharomyces cerevisiae as a model

Ricin produced by the castor bean plant and Shiga toxins produced by pathogenic Escherichia coli (STEC) and Shigella dysenteriae are type II ribosome inactivating proteins (RIPs), containing an enzymatically active A subunit that inhibits protein synthesis by removing an adenine from the α-sarcin/ricin loop (SRL) of the 28S rRNA. There are currently no known antidotes to Shiga toxin or ricin, and the ability to screen large chemical libraries for inhibitors has been hindered by lack of quantitative assays for catalytic activity that can be adapted to a high throughput format. Here, we describe the development of a robust and quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay that can directly measure the toxins' catalytic activity on ribosomes and can be used to examine the kinetics of depurination in vivo. The qRT-PCR assay exhibited a much wider dynamic range than the previously used primer extension assay (500-fold vs. 16-fold) and increased sensitivity (60 pM vs. 0.57 nM). Using this assay, a 400-fold increase in ribosome depurination was observed in yeast expressing ricin A chain (RTA) relative to uninduced cells. Pteroic acid, a known inhibitor of enzymatic activity, inhibited ribosome depurination by RTA and Shiga toxin 2 with an IC(50) of ∼ 100 μM, while inhibitors of ricin transport failed to inhibit catalytic activity. These results demonstrate that the qRT-PCR assay would enable refined kinetic studies with RIPs and could be a powerful screening tool to identify inhibitors of catalytic activity.

Effects of tetrahydropterines on the generation of quinones catalyzed by tyrosinase

Tetrahydrobiopterine (6BH(4)) can diminish the oxidative stress undergone by keratinocytes and melanocytes by reducing the o-quinones generated by the oxidation of the corresponding o-diphenols. We found that 6BH(4) and their analogs reduced all the o-quinones studied. The formal potentials of different quinone/diphenol pairs indicate that the o-quinones with withdrawing groups are more potent oxidants than those with donating groups.

Effects of sepiapterin supplementation and NOS inhibition on glucocorticoid-induced hypertension

BACKGROUND

Glucocorticoid-induced hypertension is associated with imbalance between nitric oxide (NO) and superoxide. One of the pathways that causes this imbalance is endothelial NO synthase (eNOS) uncoupling. In the present study, adrenocorticotrophic hormone (ACTH)- and dexamethasone-treated rats were further treated with sepiapterin, a precursor of tetrahydrobiopterin, or N-nitro-L-arginine (NOLA), an inhibitor of NOS, to investigate the role of eNOS uncoupling in glucocorticoid-induced hypertension.

METHODS

Male Sprague-Dawley (SD) rats (n = 7-13/group) were treated with either sepiapterin (5 mg/kg/day, IP) or saline (sham) 4 days before and during ACTH (0.2 mg/kg/day, SC), dexamethasone (0.03 mg/kg/day, SC), or saline treatment. NOLA (0.4 mg/ml in drinking water) was given to rats 4 days before and during dexamethasone treatment. Systolic blood pressure (SBP) was measured by the tail-cuff method.

RESULTS

Both ACTH (116 +/- 2 to 135 +/- 3 mm Hg (mean +/- s.e.m.), P < 0.001) and dexamethasone (114 +/- 4 to 133 +/- 3 mm Hg, P < 0.0005) increased SBP. Sepiapterin alone did not alter SBP. Sepiapterin did not prevent ACTH- (129 +/- 4 mm Hg, NS) or dexamethasone-induced hypertension (135 +/- 3 mm Hg, NS), although plasma total biopterin concentrations were increased. NOLA increased SBP in rats prior to dexamethasone or saline treatment. NOLA further increased SBP in both saline- (133 +/- 4 to 157 +/- 3 mm Hg, P < 0.05) and dexamethasone-treated rats (135 +/- 5 to 170 +/- 6 mm Hg, P < 0.05). ACTH and dexamethasone increased plasma F(2)-isoprostane concentrations. Neither sepiapterin nor NOLA significantly affected this marker of oxidative stress.

CONCLUSION

Sepiapterin did not prevent ACTH- or dexamethasone-induced hypertension. NOLA exacerbated dexamethasone-induced hypertension. These data suggest that eNOS uncoupling does not play a major role in the genesis of glucocorticoid-induced hypertension in the rat.

Hyperglycemia adversely modulates endothelial nitric oxide synthase during anesthetic preconditioning through tetrahydrobiopterin- and heat shock protein 90-mediated mechanisms

BACKGROUND

Endothelial nitric oxide synthase activity is regulated by (6R-)5,6,7,8-tetrahydrobiopterin (BH4) and heat shock protein 90. The authors tested the hypothesis that hyperglycemia abolishes anesthetic preconditioning (APC) through BH4- and heat shock protein 90-dependent pathways.

METHODS

Myocardial infarct size was measured in rabbits in the absence or presence of APC (30 min of isoflurane), with or without hyperglycemia, and in the presence or absence of the BH4 precursor sepiapterin. Isoflurane-dependent nitric oxide production was measured (ozone chemiluminescence) in human coronary artery endothelial cells cultured in normal (5.5 mm) or high (20 mm) glucose conditions, with or without sepiapterin (10 or 100 microm).

RESULTS

APC decreased myocardial infarct size compared with control experiments (26 +/- 6% vs. 46 +/- 3%, respectively; P < 0.05), and this action was blocked by hyperglycemia (43 +/- 4%). Sepiapterin alone had no effect on infarct size (46 +/- 3%) but restored APC during hyperglycemia (21 +/- 3%). The beneficial actions of sepiapterin to restore APC were blocked by the nitric oxide synthase inhibitor N (G)-nitro-L-arginine methyl ester (47 +/- 2%) and the BH4 synthesis inhibitor N-acetylserotonin (46 +/- 3%). Isoflurane increased nitric oxide production to 177 +/- 13% of baseline, and this action was attenuated by high glucose concentrations (125 +/- 6%). Isoflurane increased, whereas high glucose attenuated intracellular BH4/7,8-dihydrobiopterin (BH2) (high performance liquid chromatography), heat shock protein 90-endothelial nitric oxide synthase colocalization (confocal microscopy) and endothelial nitric oxide synthase activation (immunoblotting). Sepiapterin increased BH4/BH2 and dose-dependently restored nitric oxide production during hyperglycemic conditions (149 +/- 12% and 175 +/- 9%; 10 and 100 microm, respectively).

CONCLUSION

The results indicate that tetrahydrobiopterin and heat shock protein 90-regulated endothelial nitric oxide synthase activity play a central role in cardioprotection that is favorably modulated by volatile anesthetics and dysregulated by hyperglycemia. Enhancing the production of BH4 may represent a potential therapeutic strategy.

eNOS uncoupling and endothelial dysfunction in aged vessels

Endothelial nitric oxide synthase (eNOS) uncoupling is a mechanism that leads to endothelial dysfunction. Previously, we reported that shear stress-induced release of nitric oxide in vessels of aged rats was significantly reduced and was accompanied by increased production of superoxide (18, 27). In the present study, we investigated the influence of aging on eNOS uncoupling. Mesenteric arteries were isolated from young (3 mo) and aged (24 mo) C57 BL/6J mice. The expression of eNOS protein in young vs. aged mice was not significantly different. However, the aged mice had remarkable increases in the ratio of eNOS monomers to dimers and N(omega)-nitro-l-arginine methyl ester-inhibitable superoxide formation. The level of nitrotyrosine in the total protein and precipitated eNOS of aged vessels was increased compared with that in young vessels. HPLC analysis indicated a reduced level of tetrahydrobiopterin (BH4), an essential cofactor for eNOS, in the mesenteric arteries of aged mice. Quantitative PCR results implied that the diminished BH4 may result from the decreased expressions of GTP cyclohydrolase I and sepiapterin reductase, enzymes involved in BH4 biosynthesis. When isolated and cannulated second-order mesenteric arteries (approximately 150 microm) from aged mice were treated with sepiapterin, acetylcholine-induced, endothelium-dependent vasodilation improved significantly, which was accompanied by stabilization of the eNOS dimer. These data suggest that eNOS uncoupling and increased nitrosylation of eNOS, decreased expressions of GTP cyclohydrolase I and sepiapterin reductase, and subsequent reduced BH4 bioavailability may be important contributors of endothelial dysfunction in aged vessels.

Role of tetrahydrobiopterin in resistance to myocardial ischemia in Brown Norway and Dahl S rats

Previously we showed that Brown Norway (BN/Mcw) rats are more resistant to myocardial ischemia-reperfusion (I/R) injury than Dahl S (SS/Mcw) rats due to increased nitric oxide (x NO) generation secondary to increased heat shock protein 90 (HSP90) association with endothelial nitric oxide synthase (NOS3). Here we determined whether increased resistance to I/R injury in BN/Mcw hearts is also related to tetrahydrobiopterin (BH(4)) and GTP cyclohydrolase I (GCH-1), the rate-limiting enzyme for BH(4) synthesis. We observed that BH(4) supplementation via sepiapterin (SP) and inhibition of GCH-1 via 2,4-diamino-6-hydroxypyrimidine (DAHP) differentially modulate cardioprotection and that SP alters the association of HSP90 with NOS3. BH(4) levels were significantly higher and 7,8-dihydrobiopterin (BH(2)) levels were significantly lower in BN/Mcw than in SS/Mcw hearts. The BH(4)-to-BH(2) ratio in BN/Mcw was more than two times that in SS/Mcw hearts. After I/R, BH(4) decreased and BH(2) increased in hearts from both strains compared with their preischemia levels. However, the increase in BH(2) in SS/Mcw hearts was significantly higher than in BN/Mcw hearts. Real-time PCR revealed that BN/Mcw hearts contained more GCH-1 transcripts than SS/Mcw hearts. SP increased recovery of left ventricular developed pressure (rLVDP) following I/R as well as decreased superoxide (O(2)(x-)) and increased x NO in SS/Mcw hearts but not in BN/Mcw hearts. DAHP decreased rLVDP as well as increased O(2)(x-) and decreased x NO in BN/Mcw hearts compared with controls but not in SS/Mcw hearts. SP increased the association of HSP90 with NOS3. These data indicate that BH(4) mediates resistance to I/R by acting as a cofactor and enhancing HSP90-NOS3 association.

Tetrahydrobiopterin in the prevention of hypertonia in hypoxic fetal brain

OBJECTIVE

Tetrahydrobiopterin (BH(4)) deficiency is a cause of dystonia at birth. We hypothesized that BH(4) is a developmental factor determining vulnerability of the immature fetal brain to hypoxic-ischemic injury and subsequent motor deficits in newborns.

METHODS

Pregnant rabbits were subjected to 40-minute uterine ischemia, and fetal brains were investigated for global and focal changes in BH(4). Newborn kits were assessed by neurobehavioral tests following vehicle and sepiapterin (BH(4) analog) treatment of dams.

RESULTS

Naive fetal brains at 70% gestation (E22) were severely deficient for BH(4) compared with maternal and other fetal tissues. BH(4) concentration rapidly increased normally in the perinatal period, with the highest concentrations found in the thalamus compared with basal ganglia, frontal, occipital, hippocampus, and parietal cortex. Global sustained 40-minute hypoxia-ischemia depleted BH(4) in E22 thalamus and to a lesser extent in basal ganglia, but not in the frontal, occipital, and parietal regions. Maternal supplementation prior to hypoxia-ischemia with sepiapterin increased BH(4) in all brain regions and especially in the thalamus, but did not increase the intermediary metabolite, 7,8-BH(2). Sepiapterin treatment also reduced incidence of severe motor deficits and perinatal death following E22 hypoxia-ischemia.

INTERPRETATION

We conclude that early developmental BH(4) deficiency plays a critical role in hypoxic-ischemic brain injury. Increasing brain BH(4) via maternal supplementation may be an effective strategy in preventing motor deficits from antenatal hypoxia-ischemia.

In silico structure-based design of a novel class of potent and selective small peptide inhibitor of Mycobacterium tuberculosis Dihydrofolate reductase, a potential target for anti-TB drug discovery

The worldwide TB structural genomics initiative has identified several new drug targets for Mycobacterium tuberculosis (M. tb). Dihydrofolate reductase (DHFR) catalyzes the NADPH-dependent reduction of dihydrofolate to tetrahydrofolate that is essential for DNA synthesis. Inhibition of its activity leads to arrest of DNA synthesis and hence cell death. Thus, M. tb DHFR (mtDHFR) is an attractive novel drug target for developing anti-TB drugs. Structural comparison of mtDHFR and human DHFR (hDHFR) reveals key differences in the active sites. These differences can be exploited for the design of selective inhibitors for mtDHFR. Based on the recently determined high resolution crystal structure of mtDHFR complexed with known inhibitor methotrexate (MTX) and cofactor NADPH, a tri-peptide inhibitor has been identified using a structure-based drug design approach. Docking studies indicate that the designed tripeptide inhibitor has a high potency (K (d) = 1.78 nM) and is a selective (approximately 120 fold over hDHFR) inhibitor for mtDHFR. Hence, the tripeptide is a suitable lead compound for the development of novel anti-TB drugs.

Enhancement of Radiation-induced Apoptosis by 6-Formylpterin

Radiation-induced apoptosis and its possible enhancement in the presence of 6-formylpterin (6-FP), a metabolite of folic acid, were examined in human myelomonocytic lymphoma U937 cells. When cells were treated with 6-FP at a nontoxic concentration of 300 microM, and then exposed to X-rays at a dose of 10 Gy, significant enhancement of radiation-induced apoptosis as determined by nuclear morphological change, phosphatidylserine (PS) externalization and DNA fragmentation were observed. Flow cytometry for the detection of intracellular hydrogen peroxide (H2O2) revealed that 6-FP increased the formation of intracellular H2O2, which further increased when the cells were irradiated. Decrease of mitochondria trans-membrane potential (MMP), release of cytochrome c from mitochondria, and activation of caspase-3 were enhanced after the combined treatment. Remarkable activation of protein kinase C delta (PKC delta) and its translocation from cytosol to mitochondria were detected in combined treatment. Increase of intracellular Ca2+ concentrations ([Ca2+]i) was also observed, however, neither calpain I nor calpain II could inhibit the apoptosis. In addition, c-Jun NH2-terminal kinase (JNK) activation was not enhanced in the combined treatment. A protein involved in a caspase-independent apoptosis pathway, apoptosis inducing factor (AIF), remained unchanged even 3 h after treatment. These results indicate that intracellular H2O2 generated by 6-FP enhances radiation-induced apoptosis via the mitochondria-mediated caspase-dependent pathway, with the active involvement of PKC delta.

Gene expression in enhanced apoptosis of human lymphoma U937 cells treated with the combination of different free radical generators and hyperthermia

The effects of various free radicals derived from 6-formylpterin (6-FP), alpha-phenyl-tert-butyl nitrone (PBN) and 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) combined with hyperthermia, on gene expression in similarly enhanced apoptosis of human lymphoma U937 cells were investigated using cDNA microarrays containing approximately 16,600 genes and computational gene expression analysis tools. When the cells were treated for 10 min at 44 degrees C (15% apoptosis level), 39 up-regulated and 3 down-regulated genes were identified. In the up-regulated genes, apoptosis- and unfolded protein response-associated genes were contained. The combined treatment with heat and either chemical enhanced apoptosis level (approximately 30%) and showed a chemical-specific gene expression pattern. Furthermore, the expression levels of selected genes were confirmed by a real-time quantitative PCR. The present results will provide a basis for further understanding the molecular mechanisms in enhancement of heat-induced apoptosis by different intracellular oxidative stress.

Sepiapterin reductase regulation of endothelial tetrahydrobiopterin and nitric oxide bioavailability

Sepiapterin reductase (SPR) catalyzes the final step of tetrahydrobiopterin (H(4)B) biosynthesis and the first step of H(4)B regeneration from an exogenous precursor sepiapterin. Despite the potential significance of SPR in regulating H(4)B-dependent nitric oxide (NO(*)) production, the endothelium-specific sequence and functions of SPR remain elusive. We first cloned endothelial SPR cDNA from bovine aortic endothelial cells (Genebank: DQ978331). In cells transiently transfected with SPR gene, SPR activity (HPLC) was dramatically increased by 19-fold, corresponding to a significant increase in endothelial H(4)B content (HPLC) and NO(*) production (electron spin resonance). In vivo delivery of SPR gene significantly increased vascular SPR protein expression (mouse vs. bovine antibodies to differentiate endogenous vs. exogenous), activity, H(4)B content, and NO(*) production, as well as NO(*)-dependent vasorelaxation. In endothelial cells transfected with small interfering RNA specific for SPR, approximately 87% of mRNA were attenuated (real-time quantitative RT-PCR), corresponding to a significant reduction in SPR protein expression and activity, which was associated with decreases in both intracellular H(4)B content and NO(*) level. Exogenous administration of sepiapterin to endothelial cells significantly upregulated H(4)B and NO(*) levels, which were attenuated by SPR RNA interference (RNAi). H(4)B-stimulated increase in NO(*) production, however, was SPR RNAi independent. GTP cyclohydrolase 1 expression and activity, as well as dihydrofolate reductase expression, were not affected by SPR RNAi, whereas dihydrofolate reductase activity was significantly downregulated. These data represent the first to study endothelial SPR functionally and clearly demonstrate an important role of endothelial SPR in modulating H(4)B and NO(*) bioavailability.

Sepiapterin decreases acute rejection and apoptosis in cardiac transplants independently of changes in nitric oxide and inducible nitric-oxide synthase dimerization

Tetrahydrobiopterin (BH(4)), a cofactor of inducible nitric-oxide synthase (iNOS), is an important post-translational regulator of NO bioactivity. We examined whether treatment of cardiac allograft recipients with sepiapterin [S-(-)-2-amino-7,8-dihydro-6-(2-hydroxy-1-oxopropyl)-4-(1H)-pteridinone], a precursor of BH(4), inhibited acute rejection and apoptosis in cardiac transplants. Heterotopic cardiac transplantation was performed in Wistar-Furth donor to Lewis recipient strain rats. Recipients were treated daily after transplantation with 10 mg/kg sepiapterin. Grafts were harvested on post-transplant day 6 for analysis of BH(4) (high-performance liquid chromatography), expression of inflammatory cytokines (reverse transcription- and real-time polymerase chain reaction), iNOS (Western blots), and NO (Griess reaction and NO analyzer). Histological rejection grade was scored, and graft function was determined by echocardiography. Apoptosis, protein nitration, and oxidative stress were determined by immunohistochemistry. Treatment of allografts with sepiapterin increased cardiac BH(4) levels by 3-fold without changing protein levels of GTP cyclohydrolase, the enzyme that regulates de novo BH(4) synthesis. Sepiapterin decreased inflammatory cell infiltrate and significantly inhibited histological rejection scores and apoptosis similar in magnitude to cyclosporine. Sepiapterin also decreased nitrative and oxidative stress. Sepiapterin caused a smaller increase in left ventricular mass versus untreated allografts but without improving fractional shortening. Sepiapterin did not alter tumor necrosis factor-alpha and interferon-gamma expression, whereas it decreased interleukin (IL)-2 expression. Sepiapterin did not change total iNOS protein or monomer levels, or plasma and tissue NO metabolites levels. It is concluded that the mechanism(s) of antirejection are due in part to decreased apoptosis, protein nitration, and oxidation of cardiomyocytes, which seems to be mediated at the immune level by limiting inflammatory cell infiltration via decreased IL-2-mediated T-lymphocyte expansion.

A unique dual activity amino acid hydroxylase in Toxoplasma gondii

The genome of the protozoan parasite Toxoplasma gondii was found to contain two genes encoding tyrosine hydroxylase; that produces l-DOPA. The encoded enzymes metabolize phenylalanine as well as tyrosine with substrate preference for tyrosine. Thus the enzymes catabolize phenylalanine to tyrosine and tyrosine to l-DOPA. The catalytic domain descriptive of this class of enzymes is conserved with the parasite enzyme and exhibits similar kinetic properties to metazoan tyrosine hydroxylases, but contains a unique N-terminal extension with a signal sequence motif. One of the genes, TgAaaH1, is constitutively expressed while the other gene, TgAaaH2, is induced during formation of the bradyzoites of the cyst stages of the life cycle. This is the first description of an aromatic amino acid hydroxylase in an apicomplexan parasite. Extensive searching of apicomplexan genome sequences revealed an ortholog in Neospora caninum but not in Eimeria, Cryptosporidium, Theileria, or Plasmodium. Possible role(s) of these bi-functional enzymes during host infection are discussed.

Deficient BH4 production via de novo and salvage pathways regulates NO responses to cytokines in adult cardiac myocytes

Adult rat cardiac myocytes typically display a phenotypic response to cytokines manifested by low or no increases in nitric oxide (NO) production via inducible NO synthase (iNOS) that distinguishes them from other cell types. To better characterize this response, we examined the expression of tetrahydrobiopterin (BH4)-synthesizing and arginine-utilizing genes in cytokine-stimulated adult cardiac myocytes. Intracellular BH4 and 7,8-dihydrobiopterin (BH2) and NO production were quantified. Cytokines induced GTP cyclohydrolase and its feedback regulatory protein but with deficient levels of BH4 synthesis. Despite the induction of iNOS protein, cytokine-stimulated adult cardiac myocytes produced little or no increase in NO versus unstimulated cells. Western blot analysis under nonreducing conditions revealed the presence of iNOS monomers. Supplementation with sepiapterin (a precursor of BH4) increased BH4 as well as BH2, but this did not enhance NO levels or eliminate iNOS monomers. Similar findings were confirmed in vivo after treatment of rat cardiac allograft recipients with sepiapterin. It was found that expression of dihydrofolate reductase, required for full activity of the salvage pathway, was not detected in adult cardiac myocytes. Thus, adult cardiac myocytes have a limited capacity to synthesize BH4 after cytokine stimulation. The mechanisms involve posttranslational factors impairing de novo and salvage pathways. These conditions are unable to support active iNOS protein dimers necessary for NO production. These findings raise significant new questions about the prevailing understanding of how cytokines, via iNOS, cause cardiac dysfunction and injury in vivo during cardiac inflammatory disease states since cardiac myocytes are not a major source of high NO production.

Acute inhibition of guanosine triphosphate cyclohydrolase 1 uncouples endothelial nitric oxide synthase and elevates blood pressure

GTP cyclohydrolase 1 (GTPCH1) is the rate-limiting enzyme in de novo synthesis of tetrahydrobiopterin (BH4), an essential cofactor for endothelial NO synthase (eNOS) dictating, at least partly, the balance of NO and superoxide produced by this enzyme. The aim of this study was to determine the effect of acute inhibition of GTPCH1 on BH4, eNOS function, and blood pressure (BP) in vivo. Exposure of bovine or mouse aortic endothelial cells to GTPCH1 inhibitors (2,4-diamino-6-hydroxypyrimidine or N-acetyl-serotonin) or GTPCH1 small-interference RNA (siRNA) significantly reduced BH4 and NO levels but increased superoxide levels. This increase was abolished by sepiapterin (BH4 precursor) or N(G)-nitro-L-arginine methyl ester (nonselective NOS inhibitor). Incubation of isolated murine aortas with 2,4-diamino-6-hydroxypyrimidine or N-acetyl-serotonin impaired acetylcholine-induced endothelium-dependent relaxation but not endothelium-independent relaxation. Aortas from GTPCH1 siRNA-injected mice, but not their control-siRNA injected counterparts, also exhibited impaired endothelium-dependent relaxation. BH4 reduction induced by GTPCH1 siRNA injection was associated with increased aortic levels of superoxide, 3-nitrotyrosine, and adhesion molecules (intercellular adhesion molecule 1 and vascular cell adhesion molecule 1), as well as a significantly elevated systolic, diastolic, and mean BP in C57BL6 mice. GTPCH1 siRNA was unable to elicit these effects in eNOS(-/-) mice. Sepiapterin supplementation, which had no effect on high BP in eNOS(-/-) mice, partially reversed GTPCH1 siRNA-induced elevation of BP in wild-type mice. In conclusion, GTPCH1 via BH4 maintains normal BP and endothelial function in vivo by preserving NO synthesis by eNOS.

Plasma cytokine concentration changes induced by the antitumor agents dipterinyl calcium pentahydrate (DCP) and related calcium pterins

Analysis of plasma cytokine concentration changes determined that oral dosing with the antitumor agent (1:4 mol:mol) calcium pterin (CaPterin) increased plasma IL-10, decreased plasma IL-6, and decreased plasma IFN-gamma concentrations in nude mice with MDA-MB-231 xenograph tumors [Moheno, P., Pfleiderer, W., Dipasquale, A.G., Rheingold, A.L., Fuchs, D., 2008. Cytokine and IDO metabolite changes effected by calcium pterin during inhibition of MDA-MB-231 xenograph tumors in nude mice. Int. J. Pharm. 355, 238-248]. A further analysis, reported here, of plasma cytokine concentration changes in nude mice with the same tumor xenographs treated with dipterinyl calcium pentahydrate (DCP), (1:2 mol:mol) calcium pterin, and CaCl(2).2H(2)O has been carried out. The measured cytokines included: IL-1beta, IL-2, IL-4, IL-6, IL-10, IL-12, IFN-gamma, and TNF-alpha. The major preliminary findings from the analyses of these data are that (1) the overall relative tumor volumes for the treatments correlated significantly with a full study antitumor plasma cytokine pattern (fsAPCP), a composite measure consisting of decreased plasma IL-6 and increased IL-4 concentrations, and (2) DCP induces a significant threshold antitumor response strongly correlated to a derived DCP antitumor plasma cytokine pattern (DCP/APCP) consisting of plasma IL-12, IL-6, and IL-4 concentration changes. This DCP/APCP composite measure identifies plasma IL-12 concentration increases, plasma IL-6 concentration decreases, and plasma IL-4 concentration increases correlated to relative tumor volume decreases caused by DCP dosing. The finding that the novel calcium pterins and CaCl(2).2H(2)O treatments decrease plasma IL-6 concentrations corroborates the previous finding that CaPterin dosing decreases plasma IL-6 concentrations in this mouse/tumor system [Moheno, P., Pfleiderer, W., Dipasquale, A.G., Rheingold, A.L., Fuchs, D., 2008. Cytokine and IDO metabolite changes effected by calcium pterin during inhibition of MDA-MB-231 xenograph tumors in nude mice. Int. J. Pharm. 355, 238-248].

Ageing diminishes endothelium-dependent vasodilatation and tetrahydrobiopterin content in rat skeletal muscle arterioles

Ageing reduces endothelium-dependent vasodilatation through an endothelial nitric oxide synthase (NOS) signalling pathway. The purpose of this study was to determine whether arginase activity diminishes endothelium-dependent vasodilatation in skeletal muscle arterioles from old rats, and whether NOS substrate (L-arginine) and cofactor (tetrahydrobiopterin; BH(4)) concentrations are reduced. First-order arterioles were isolated from the soleus muscle of young (6 months old) and old (24 months old) male Fischer 344 rats. In vitro changes in luminal diameter in response to stepwise increases in flow were determined in the presence of the NOS inhibitor N(G)-nitro-L-arginine methyl ester (l-NAME, 10(-5) mol l(-1)), the arginase inhibitor N(omega)-hydroxy-nor-L-arginine (NOHA, 5 x 10(-4) mol l(-1)), exogenous L-arginine (3 x 10(-3) mol l(-1)) or the precursor for BH(4) synthesis sepiapterin (1 micromol l(-1)). Arteriolar L-arginine and BH(4) content were determined via HPLC. Ageing decreased flow-mediated vasodilatation by 52%, and this difference was abolished with NOS inhibition. Neither inhibition of arginase activity nor addition of exogenous L-arginine had any effect on flow-mediated vasodilatation; arteriolar l-arginine content was also not different between age groups. BH(4) content was lower in arterioles from old rats (94 +/- 8 fmol (mg tissue)(-1)) relative to controls (234 +/- 21 fmol (mg tissue)(-1)), and sepiapterin elevated flow-mediated vasodilatation in arterioles from old rats. These results demonstrate that the impairment of endothelium-dependent vasodilatation induced by old age is due to an altered nitric oxide signalling mechanism in skeletal muscle arterioles, but is not the result of increased arginase activity and limited L-arginine substrate. Rather, the age-related deficit in flow-mediated vasodilatation appears to be the result, in part, of limited BH(4) bioavailability.

Nitration of soluble proteins in organotypic culture models of Parkinson's disease

Protein nitration due to oxidative and nitrative stress has been linked to the pathogenesis of Parkinson's disease (PD), but its relationship to the loss of dopamine (DA) or tyrosine hydroxylase (TH) activity is not clear. Here we quantified protein-bound 3-nitrotyrosine (3-NT) by a novel gas chromatography/negative chemical ionization tandem mass spectrometry technique and DA and 3,4-dihydroxyphenylalanine (DOPA) by HPLC in tissues or medium of organotypic, mouse mesencephalon cultures after acute or chronic treatments with the peroxynitrite donor 3-morpholino-sydnonimine (SIN-1), the dopaminergic toxin 1-methyl-4-phenylpyridinium (MPP(+)) or the lipophilic complex I inhibitor rotenone. Incubation with SIN-1 (24 h) or MPP(+) treatments (48 h) caused dose-dependent protein nitration reaching a maximum of eightfold increase by 10 mM SIN-1 or twofold by 10 microM MPP(+), but significant DA depletions occurred at much lower concentrations of MPP(+) (1 microM). Chronic MPP(+) or rotenone treatments (3 weeks) caused maximum protein nitration by 1 microM (twofold) or 10nM (fourfold), respectively. Co-treatment with the nitric oxide synthase inhibitor l-NAME (300 microM) prevented protein nitration by MPP(+), but did not protect against MPP(+)-induced DA depletion or inhibition of TH activity. Acute incubation with 100 microM SIN-1 inhibited TH activity, which could be blocked by co-treatment with the tetrahydrobiopterin precursor l-sepiapterin, but tissue DA depletions required higher doses of SIN-1 (>1 mM, 24 h) and longer survival. In conclusion, protein nitration and TH activity or DA depletion are not directly related in these models.

C-reactive protein decreases endothelial nitric oxide synthase activity via uncoupling

C-reactive protein (CRP), a cardiovascular risk marker, induces endothelial dysfunction. We have previously shown that CRP decreases endothelial nitric oxide synthase (eNOS) expression and bioactivity in human aortic endothelial cells (HAECs). In this study, we examined the mechanisms by which CRP decreases eNOS activity in HAECs. To this end, we explored different strategies such as availability of tetrahydrobiopterin (BH4)-a critical cofactor for eNOS, superoxide (O(2)(-)) production resulting in uncoupling of eNOS and phosphorylation/dephosphorylation of eNOS. CRP treatment significantly decreased levels of BH4 thereby promoting eNOS uncoupling. Pretreatment with sepiapterin, a BH4 precursor, prevented CRP-mediated effects on BH(4) levels, superoxide production as well as eNOS activity. The gene expression and enzymatic activity of GTPCH1, the first enzyme in the de novo biosynthesis of BH(4), were significantly inhibited by CRP. Importantly, GTPCH1 is known to be regulated by cAMP-mediated pathway. In the present study, CRP-mediated inhibition of GTPCH1 activity was reversed by pretreatment with cAMP analogues. Furthermore, CRP-induced O(2)(-) production was reversed by pharmacologic inhibition and siRNAs to p47 phox and p22 phox. Additionally, CRP treatment significantly decreased the eNOS dimer: monomer ratio confirming CRP-mediated eNOS uncoupling. The pretreatment of cells with NO synthase inhibitor (N-nitro-l-arginine methyl ester [l-NAME]) also prevented CRP-mediated O(2)(-) production further strengthening CRP-mediated eNOS uncoupling. Additionally, CRP decreased eNOS phosphorylation at Ser1177 as well as increased phosphorylation at Thr495. CRP appears to mediate these effects through the Fcgamma receptors, CD32 and CD64. To conclude, CRP uncouples eNOS resulting in increased superoxide production, decreased NO production and altered eNOS phosphorylation.

Oxidative stress and increased eNOS and NADPH oxidase expression in mouse microvessel endothelial cells

Elevated oxidative stress plays a key role in diabetes-associated vascular disease. In this study, we tested the hypothesis that high glucose-induced oxidative stress was associated with changes in the expression of NADPH oxidase, superoxide dismutase (SOD) and endothelial nitric oxide synthase (eNOS). Oxidative stress was assessed in cell cultures of mouse microvessel endothelial cells (MMECs) by fluorescence labelling with dihydroethidium, lucigenin-enhanced chemiluminescence and determining NADPH oxidase subunit and eNOS expression with real-time polymerase chain reaction protocol and Western blotting. Oxidative stress and expression of the NADPH oxidase subunit, p22phox, were both increased, SOD1 and 3 expression lowered and eNOS significantly elevated in MMECs treated with 40 mM glucose for 72 h compared to low glucose medium. Oxidative stress, p22phox mRNA, eNOS mRNA, and protein were lowered by concurrent incubation with sepiapterin. When eNOS protein expression in endothelial cells was significantly decreased by eNOS siRNA treatment, superoxide generation was significantly higher in the MMECs grown in low glucose, but reduced in those grown in high glucose for 72 h. Thus, exposure of MMECs to high glucose results in increased oxidative stress that is associated with increased eNOS and NADPH oxidase subunit expression, notably p22phox, and decreased expression of SOD1 and 3.

Comparative preclinical activity of the folate-targetedVinca alkaloid conjugates EC140 and EC145

EC140 is a water soluble folate conjugate of desacetylvinblastine monohydrazide (DAVLBH), which is constructed with an endosome-cleavable acyl hydrazone bond. This agent has proven to be active and specific against well established, subcutaneous folate receptor (FR)-positive tumors in multiple animal models. Recent structure-activity and optimization studies have yielded a disulfide bond-containing counterpart to EC140, herein referred to as EC145. This new conjugate was found to retain high affinity for FR-positive cells, and it produced specific, dose-responsive activity in vitro. Comparative in vivo efficacy tests confirmed that, like EC140, EC145 displays activity against both syngeneic and xenograft tumor models. However, EC145 was found to be more active and better tolerated than EC140; hence, more durable complete responses were consistently observed in EC145-treated tumor-bearing animals. Furthermore, EC145 was not found to be active against a FR-negative tumor model. Additional preclinical studies are therefore warranted to better understand EC145's breadth of activity against FR-positive tumors.

Calcium-pterin suppresses mitogen-induced tryptophan degradation and neopterin production in peripheral blood mononuclear cells

Antitumor activity of a calcium-pterin suspension has been described in vitro and in animal model systems. Recent studies provide some evidence that this effect involves immune-mediated mechanisms. We investigated the influence of calcium-pterin on freshly isolated human peripheral blood mononuclear cells (PBMC) stimulated with the mitogens phytohaemagglutinin and concanavalin A in vitro. Influence of calcium-pterin on tryptophan-degrading enzyme indoleamine (2,3)-dioxygenase (IDO) and on neopterin production was monitored in supernatants of cells. Increased neopterin concentrations as well as accelerated tryptophan degradation have been found to predict poor prognosis in patients with cancer, and both these immunobiochemical pathways are induced by the pro-inflammatory cytokine interferon-gamma. Compared to unstimulated cells, mitogens induced degradation of tryptophan and formation of neopterin in PBMC, and upon addition of calcium-pterin, both biochemical results were suppressed in a dose-dependent way. Thus, calcium-pterin suppresses immunological pathways in vitro that in patients with malignant diseases characterize an unfavorable prognosis. The effect of the compound to suppress IDO activity could be of considerable relevance for the antitumoral effect of the compound because activation of the enzyme is considered as an immune-escape mechanism of tumor cells.

Tetrahydrobiopterin stimulates L-DOPA release from striatal tissue

In the present study we have analyzed the effect of tetrahydrobiopterin (BH4) essential cofactor for tyrosine hydroxylase and nitric oxide synthase, on the 3,4-dihydroxyphenylalanine (L-DOPA) release from in vitro incubated striatal tissue. dl-6-methyl-5,6,7,8 tetrahydropterine (6-MPH4)-stimulated L-DOPA release in a concentration-dependent manner in the range from 25 to 100 microM. At these concentrations 6-MPH4 did not have any effect on dopamine release. Presence of Nomega-Nitro-L-arginine methyl ester (L-NAME, 200 microM), a nitric oxide synthase inhibitor, but not of alpha-methyl-rho-tyrosine (alpha-MPT, 100 microM), a tyrosine hydroxylase inhibitor, blocked L-DOPA release induced by 6-MPH4 (200 microM). Also, the addition to the incubation medium of melatonin (MEL, 300 microM), which is a scavenger of NO and other free radicals, blocked the L-DOPA release induced by 6-MPH4 (200 microM) but this effect did not occur with the addition of the peroxynitrite scavenger uric acid (UA, 300 microM). Sodium nitroprusside (SNP, 100 muM), a NO generator and l-DOPA releaser as previously reported, potentiated the L-DOPA releasing effect of 6-MPH4 (200 microM) which was also blocked by melatonin. In summary 6-MPH4 stimulates L-DOPA release from striatal fragments incubated in vitro by a mechanism which involves NO or other free radicals derived from NO but not peroxynitrite.

eNOS gene therapy exacerbates hepatic ischemia-reperfusion injury in diabetes: a role for eNOS uncoupling

Previous studies indicate that endothelial nitric oxide synthase (eNOS) function is impaired in diabetes as a result of increased vascular generation of reactive oxygen species. We hypothesized that eNOS gene therapy would augment NO. bioavailability and protect against hepatic ischemia-reperfusion (I-R) injury in type 2 diabetes mellitus. We developed a transgenic (Tg) diabetic mouse in which eNOS is systemically overexpressed. We also examined the effects of hepatic eNOS adenovirus therapy in diabetic mice. Diabetic (db/db) and nondiabetic mice were subjected to hepatic I-R injury. In nondiabetic mice, genetic overexpression of eNOS (both eNOS-Tg and eNOS adenovirus) resulted in hepatoprotection. In contrast, hepatic I-R injury was significantly increased in the db/db eNOS-Tg mouse, as serum alanine aminotransaminase (ALT) levels were increased by 3.3-fold compared with diabetic controls. Similarly, eNOS adenovirus treatment resulted in a 3.2-fold increase in serum ALT levels as compared with diabetic controls. We determined that hepatic eNOS was dysfunctional in the db/db mouse and increased genetic expression of eNOS resulted in greater production of peroxynitrite. Treatment with the eNOS cofactor tetrahydrobiopterin (BH4) or the BH4 precursor sepiapterin resulted in a significant decrease in serum ALT levels following I-R injury. We present clear examples of the protective and injurious nature of NO. therapy in I-R. Our data indicate that eNOS exists in an "uncoupled" state in the setting of diabetes and that "recoupling" of the eNOS enzyme with cofactor therapy is beneficial.