Mechanisms for the role of tetrahydrobiopterin in endothelial function and vascular disease

Resveratrol reverses endothelial nitric-oxide synthase uncoupling in apolipoprotein E knockout mice

A crucial cause of the decreased bioactivity of nitric oxide (NO) in cardiovascular diseases is the uncoupling of the endothelial NO synthase (eNOS) caused by the oxidative stress-mediated deficiency of the NOS cofactor tetrahydrobiopterin (BH(4)). The reversal of eNOS uncoupling might represent a novel therapeutic approach. The treatment of apolipoprotein E knockout (ApoE-KO) mice with resveratrol resulted in the up-regulation of superoxide dismutase (SOD) isoforms (SOD1-SOD3), glutathione peroxidase 1 (GPx1), and catalase and the down-regulation of NADPH oxidases NOX2 and NOX4 in the hearts of ApoE-KO mice. This was associated with reductions in superoxide, 3-nitrotyrosine, and malondialdehyde levels. In parallel, the cardiac expression of GTP cyclohydrolase 1 (GCH1), the rate-limiting enzyme in BH(4) biosynthesis, was enhanced by resveratrol. This enhancement was accompanied by an elevation in BH(4) levels. Superoxide production from ApoE-KO mice hearts was reduced by the NOS inhibitor L-N(G)-nitro-arginine methyl ester, indicating eNOS uncoupling in this pathological model. Resveratrol treatment resulted in a reversal of eNOS uncoupling. Treatment of human endothelial cells with resveratrol led to an up-regulation of SOD1, SOD2, SOD3, GPx1, catalase, and GCH1. Some of these effects were preventable with sirtinol, an inhibitor of the protein deacetylase sirtuin 1. In summary, resveratrol decreased superoxide production and enhanced the inactivation of reactive oxygen species. The resulting reduction in BH(4) oxidation, together with the enhanced biosynthesis of BH(4) by GCH1, probably was responsible for the reversal of eNOS uncoupling. This novel mechanism (reversal of eNOS uncoupling) might contribute to the protective effects of resveratrol.

Donor pretreatment with tetrahydrobiopterin saves pancreatic isografts from ischemia reperfusion injury in a mouse model

Depletion of the nitric oxide synthase cofactor tetrahydrobiopterin (H4B) during ischemia and reperfusion is associated with severe graft pancreatitis. Since clinically feasible approaches to prevent ischemia reperfusion injury (IRI) by H4B-substitution are missing we investigated its therapeutic potential in a murine pancreas transplantation model using different treatment regimens. Grafts were subjected to 16 h cold ischemia time (CIT) and different treatment regimens: no treatment, 160 μM H4B to perfusion solution, H4B 50 mg/kg prior to reperfusion and H4B 50 mg/kg before recovery of organs. Nontransplanted animals served as controls. Recipient survival and endocrine graft function were assessed. Graft microcirculation was analyzed 2 h after reperfusion by intravital fluorescence microscopy. Parenchymal damage was assessed by histology and nitrotyrosine immunohistochemistry, H4B tissue levels by high pressure liquid chromatography (HPLC). Compared to nontransplanted controls prolonged CIT resulted in significant microcirculatory deterioration. Different efficacy according to route and timing of administration could be observed. Only donor pretreatment with H4B resulted in almost completely abrogated IRI-related damage showing graft microcirculation comparable to nontransplanted controls and restored intragraft H4B levels, resulting in significant reduction of parenchymal damage (p < 0.002) and improved survival and endocrine function (p = 0.0002 each). H4B donor pretreatment abrogates ischemia-induced parenchymal damage and represents a promising strategy to prevent IRI following pancreas transplantation.

Is tetrahydrobiopterin a therapeutic option in diabetic hypertensive patients?

Nitric oxide (NO) is an important regulator of vascular tone, and is also an antithrombotic, anti-inflammatory, antiproliferative, and antiatherogenic factor. Endothelial function is altered in patients with coronary artery disease, stroke, and peripheral artery disease, and endothelial dysfunction correlates with the risk factor profile for a patient. Hypertension and type 2 diabetes are risk factors for vascular disease, and are both pathologies characterized by loss of NO activity. Indeed, endothelial dysfunction is usually present in diabetic and/or hypertensive patients. Tetrahydrobiopterin is an essential cofactor for the NO synthase enzyme, and insufficiency of this cofactor leads to uncoupling of the enzyme, release of superoxide, endothelial dysfunction, progression of hypertension, and finally, proatherogenic effects. Tetrahydrobiopterin is also an important mediator of NO synthase regulation in type 2 diabetes and hypertension, and may be a rational therapeutic target to restore endothelial function and prevent vascular disease in these patients. The aim of this paper is to review the rationale for therapeutic strategies directed to biopterins as a target for vascular disease in type 2 diabetic hypertensive patients.

C-terminus of heat shock protein 70-interacting protein-dependent GTP cyclohydrolase I degradation in lambs with increased pulmonary blood flow

We showed that nitric oxide (NO) signaling is decreased in the pulmonary vasculature before the development of endothelial dysfunction in a lamb model of congenital heart disease and increased pulmonary blood flow (Shunt). The elucidation of the molecular mechanism by which this occurs was the purpose of this study. Here, we demonstrate that concentrations of the endogenous NO synthase (NOS) inhibitor, asymmetric dimethylarginine (ADMA), are elevated, whereas the NOS cofactor tetrahydrobiopterin (BH(4)) is decreased in Shunt lambs. Our previous studies demonstrated that ADMA decreases heat shock protein-90 (Hsp90) chaperone activity, whereas other studies suggest that guanosine-5'-triphosphate cyclohydrolase 1 (GCH1), the rate-limiting enzyme in the generation of BH(4), may be a client protein for Hsp90. Thus, we determined whether increases in ADMA could alter GCH1 protein and activity. Our data demonstrate that ADMA decreased GCH1 protein, but not mRNA concentrations, in pulmonary arterial endothelial cells (PAECs) because of the ubiquitination and proteasome-dependent degradation of GCH1. We also found that Hsp90-GCH1 interactions were reduced, whereas the association of GCH1 with Hsp70 and the C-terminus of Hsp70-interacting protein (CHIP) increased in ADMA-exposed PAECs. The overexpression of CHIP potentiated, whereas a CHIP U-box domain mutant attenuated, ADMA-induced GCH1 degradation and reductions in cellular BH(4) concentrations. We also found in vivo that Hsp90/GCH1 interactions are decreased, whereas GCH1-Hsp70 and GCH1-CHIP interactions and GCH1 ubiquitination are increased. Finally, we found that supplementation with l-arginine restored Hsp90-GCH1 interactions and increased both BH(4) and NO(x) concentrations in Shunt lambs. In conclusion, increased concentrations of ADMA can indirectly alter NO signaling through decreased cellular BH(4) concentrations, secondary to the disruption of Hsp90-GCH1 interactions and the CHIP-dependent proteasomal degradation of GCH1.

Oral tetrahydrobiopterin improves the beneficial effect of adenoviral-mediated eNOS gene transfer after induction of hindlimb ischemia

We tested the hypothesis that oral supplementation with the endothelial nitric oxide synthase (eNOS) cofactor tetrahydrobiopterin (BH(4)) improved the therapeutic efficacy of eNOS gene transfer in the ischemic rat hindlimb. BH(4) or vehicle were begun 1 week before induction of hindlimb ischemia, whereas recombinant adenovirus containing bovine eNOS cDNA (AdeNOS) or vehicle [phosphate-buffered saline (PBS)] was infused intra-arterially into the ischemic hindlimb 10 days after induction of ischemia. Rats receiving co-treatment with dietary BH(4) and eNOS gene transfer (the [eNOS, +BH(4)] group) had greater eNOS expression, phospho-eNOS expression (Ser(1177)), Ca(2+)-dependent NOS activity, and nitrite + nitrate concentrations in the ischemic gastrocnemius than did rats receiving AdeNOS alone. The [eNOS, +BH(4)] group demonstrated less nitrotyrosine and a higher ratio of reduced:oxidized glutathione (GSH:GSSG) in the ischemic gastrocnemius muscle than did rats receiving AdeNOS alone. The [eNOS, +BH(4)] group had greater flow recovery and a higher capillary:myocyte ratio in the ischemic hindlimb than did rats receiving AdeNOS alone. Finally, the [eNOS,+BH(4)] group had less necrosis of hindlimb muscles than rats given AdeNOS alone. We conclude that adjunctive dietary therapy with BH(4) increases the beneficial effects of eNOS gene transfer within the ischemic gastrocnemius muscle, as evidenced by increased nitric oxide (NO) production, diminished oxidative stress, enhanced flow recovery, and reduced necrosis.

A review of endothelial dysfunction in diabetes: a focus on the contribution of a dysfunctional eNOS

Although the etiology of vascular dysfunction in diabetes has been extensively investigated in both humans as well as animal models of human diabetes, the relative importance of the cellular pathways involved is still not fully understood. In this review, we focus on reviewing the literature that provides insights into how an acute exposure to hyperglycemia results in a dysregulation of endothelial nitric oxide synthase function, the subsequent downstream effects of endothelial nitric oxide synthase dysregulation, and the development of endothelial dysfunction.

The role of tetrahydrobiopterin and dihydrobiopterin in ischemia/reperfusion injury when given at reperfusion

Reduced nitric oxide (NO) bioavailability and increased oxidative stress are major factors mediating ischemia/reperfusion (I/R) injury. Tetrahydrobiopterin (BH₄) is an essential cofactor of endothelial NO synthase (eNOS) to produce NO, whereas dihydrobiopterin (BH₂) can shift the eNOS product profile from NO to superoxide, which is further converted to hydrogen peroxide (H₂O₂) and cause I/R injury. The effects of BH₄ and BH₂ on oxidative stress and postreperfused cardiac functions were examined in ex vivo myocardial and in vivo femoral I (20 min)/R (45 min) models. In femoral I/R, BH₄ increased NO and decreased H₂O₂ releases relative to saline control, and these effects correlated with improved postreperfused cardiac function. By contrast, BH₂ decreased NO release relative to the saline control, but increased H₂O₂ release similar to the saline control, and these effects correlated with compromised postreperfused cardiac function. In conclusion, these results suggest that promoting eNOS coupling to produce NO and decrease H₂O₂ may be a key mechanism to restore postreperfused organ function during early reperfusion.

Trypanosoma brucei pteridine reductase 1 is essential for survival in vitro and for virulence in mice

Gene knockout and knockdown methods were used to examine essentiality of pteridine reductase (PTR1) in pterin metabolism in the African trypanosome. Attempts to generate PTR1 null mutants in bloodstream form Trypanosoma brucei proved unsuccessful; despite integration of drug selectable markers at the target locus, the gene for PTR1 was either retained at the same locus or elsewhere in the genome. However, RNA interference (RNAi) resulted in complete knockdown of endogenous protein after 48 h, followed by cell death after 4 days. This lethal phenotype was reversed by expression of enzymatically active Leishmania major PTR1 in RNAi lines ((oe)RNAi) or by addition of tetrahydrobiopterin to cultures. Loss of PTR1 was associated with gross morphological changes due to a defect in cytokinesis, resulting in cells with multiple nuclei and kinetoplasts, as well as multiple detached flagella. Electron microscopy also revealed increased numbers of glycosomes, while immunofluorescence microscopy showed increased and more diffuse staining for glycosomal matrix enzymes, indicative of mis-localisation to the cytosol. Mis-localisation was confirmed by digitonin fractionation experiments. RNAi cell lines were markedly less virulent than wild-type parasites in mice and virulence was restored in the (oe)RNAi line. Thus, PTR1 may be a drug target for human African trypanosomiasis.

Acute effects of a caffeine-containing supplement on bench press and leg extension strength and time to exhaustion during cycle ergometry

The purpose of the present study was to examine the acute effects of a caffeine-containing supplement (SUPP) on 1 repetition maximum (1RM) bench press and leg extension strength, as well as time to exhaustion (TTE), during cycle ergometry at a power output that corresponded to 80% of VO2peak. The study used a double-blinded, placebo-controlled, crossover design. Twenty-one untrained men (mean +/- SD age = 23.0 +/- 2.6 yr) were randomly assigned to take either the SUPP or placebo (PLAC) first. The SUPP contained 400 mg of caffeine, 66.7 mg of capsicum extract, 10 mg of bioperine, and 40 mg of niacin, and the PLAC was microcrystalline cellulose. Sixty minutes after taking either the SUPP or PLAC, the subjects were tested for 1RM bench press and leg extension strength, as well as TTE. After 1 week of rest, the subjects ingested the opposite substance (SUPP or PLAC) and were retested for 1RM bench press and leg extension strength, as well as TTE. The results indicated that the SUPP had no effect on 1RM bench press strength, 1RM leg extension strength, or TTE at 80% VO2peak. These findings did not support the use of the caffeine-containing SUPP in the present study as an ergogenic aid in untrained individuals.

Endothelial dysfunction in diabetes: multiple targets for treatment

Robert Furchgott's discovery of the obligatory role that the endothelium plays in the regulation of vascular tone has proved to be a major advance in terms of our understanding of the cellular basis of diabetic vascular disease. Endothelial dysfunction, as defined by a reduction in the vasodilatation response to an endothelium-dependent vasodilator (such as acetylcholine) or to flow-mediated vasodilatation, is an early indicator for the development of the micro- and macroangipathy that is associated with diabetes. In diabetes, hyperglycaemia plays a key role in the initiation and development of endothelial dysfunction; however, the cellular mechanisms involved as well as the importance of dyslipidaemia and co-morbidities such as hypertension and obesity remain incompletely understood. In this review, we discuss the mechanisms whereby hyperglycaemia, oxidative stress and dyslipidaemia can alter endothelial function and highlight their effects on endothelial nitric oxide synthase (eNOS), the endothelium-dependent hyperpolarising factor (EDHF) pathway(s), as well as on the role of endothelium-derived contracting factors (EDCFs) and adipocyte-derived vasoactive factors such as adipose-derived relaxing factor (ADRF).

Improvement of impaired endothelial function by tetrahydrobiopterin in stroke-prone spontaneously hypertensive rats

To investigate the role of tetrahydrobiopterin (BH4), an essential cofactor of nitric oxide synthase, in endothelial function in a model of genetic hypertension, acetylcholine- and sodium nitroprusside (SNP)-induced vasodilator responses were examined in the absence and presence of BH4 in age-matched adult stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats. Acetylcholine-induced depressor responses attenuated significantly in SHRSP compared with those in WKY rats. Acetylcholine-induced relaxations in phenylephrine-precontracted aortic rings of SHRSP were also significantly impaired as compared to those of WKY rats, while SNP-induced relaxations were similar between both strains. In SHRSP, intravenous infusion of BH4 (0.12 mg/kg per min for 20 min following a bolus injection of 0.48 mg/kg) significantly improved vasodilator responses to acetylcholine without affecting those to SNP, but in WKY rats BH4 did not influence those to acetylcholine. BH4 infusion itself had no hemodynamic effect in both strains. However, BH4 levels in plasma and thoracic aorta as well as plasma concentrations of nitrite plus nitrate, metabolites of NO, in SHRSP were all significantly greater than those in WKY rats, suggesting the occurrence of compensatory upregulation of NO synthesis in SHRSP. These results demonstrate that the impaired endothelial function in SHRSP cannot be explained simply by the decrease in absolute amount of BH4.

An enzymatic method to distinguish tetrahydrobiopterin from oxidized biopterins using UDP-glucose:tetrahydrobiopterin glucosyltransferase

The quantitative determination of tetrahydrobiopterin (BH4) and its oxidized forms (dihydrobiopterin and biopterin) is important in searching for possible markers of neuropsychiatric and cardiovascular disorders as well as in diagnosing BH4 deficiencies. Currently, two high-performance liquid chromatography (HPLC) methods are available, although both have some limitations. We developed an enzymatic method to distinguish BH4 from the oxidized forms by employing BH4:UDP-glucose alpha-glucosyltransferase (BGluT), which catalyzes glucosyl transfer from UDP-glucose to BH4. The recombinant BGluT isolated from Escherichia coli converted essentially all of the BH4 in a mixture containing oxidized biopterins to the glucoside while leaving the oxidized forms intact. Therefore, acidic iodine oxidation of the reaction mixture followed by single fluorescence HPLC permitted the determination of biopterin and biopterin-glucoside, which represent oxidized biopterins and BH4, respectively. The validity of the method was evaluated using authentic biopterins and animal samples such as human urine, rat plasma, and rat liver. The BGluT-catalyzed reaction not only would reduce the burden of chromatographic separation but also would promise non-HPLC analysis of BH4.

Lipoproteins, platelets and atherothrombosis

Atherosclerosis and thrombosis associated with the rupture of vulnerable plaque are the main causes of cardiovascular events, including acute coronary syndrome. Low-density lipoprotein (LDL) plays a key role in the pathogenesis of atherothrombotic processes. LDLs modify the antithrombotic properties of the vascular endothelium and change vessel contractility by reducing the availability of endothelial nitric oxide and activating proinflammatory signaling pathways. In addition, LDLs also influence the functions and interactions of cells present in atherosclerotic lesions, whether they come from the circulation or are resident in vessel walls. In fact, LDLs entering affected vessels undergo modifications (e.g. oxidation, aggregation and glycosylation) that potentiate their atherogenic properties. Once modified, these intravascular LDLs promote the formation of foam cells derived from smooth muscle cells and macrophages, thereby increasing the vulnerability of atherosclerotic plaque. Moreover, they also increase the thrombogenicity of both plaque and blood, in which circulating tissue factor levels are raised and platelet reactivity is enhanced. This review focuses on the importance of native and modified LDL for the pathogenesis of atherothrombosis. It also discusses current studies on LDL and its effects on the actions of vascular cells and blood cells, particularly platelets, and considers novel potential therapeutic targets.

Do sauna therapy and exercise act by raising the availability of tetrahydrobiopterin?

Sauna therapy has been used to treat a number of different diseases known or thought to have a tetrahydrobiopterin (BH4) deficiency. It has been interpreted to act in multiple chemical sensitivity by increasing chemical detoxification and excretion but there is no evidence that this is its main mode of action. Sauna therapy may act to increase BH4 availability via two distinct pathways. Increased blood flow in heated surface tissues leads to increased vascular shear stress, inducing increased activity of GTP cyclohydrolase I (GTPCH-I) in those vascular tissues which will lead to increasing BH4 synthesis. A second mechanism involves the heat shock protein Hsp90, which is induced by even modest heating of mammalian tissues. Sauna heating of these surface tissues may act via Hsp90, which interacts with the GTPCH-I complex and is reported to produce increased GTPCH-I activity by lowering its degradation. The increased consequent availability of BH4 may lead to lowered nitric oxide synthase uncoupling, such as has been reported for the eNOS enzyme. Increased BH4 synthesis in surface tissues of the body will produce increased circulating BH4 which will feed BH4 to other body tissues that may have been BH4 deficient. Similar mechanisms may act in vigorous exercise due to the increased blood shear stresses and possibly also heating of the exercising tissues and heart. There is a large and rapidly increasing number of diseases that are associated with BH4 depletion and these may be candidates for sauna therapy. Such diseases as hypertension, vascular endothelial dysfunction, multiple chemical sensitivity and heart failure are thought to be helped by sauna therapy and chronic fatigue syndrome and fibromyalgia may also be helped and there are others that may be good candidates for sauna therapy.

Nitric oxide regulation of autonomic function in heart failure

Nitric oxide (NO) functions at all levels of the autonomic nervous system to influence sympathetic and parasympathetic control of cardiovascular function. It modulates the excitability of peripheral sensory and motor neurons of cardiovascular reflexes and the central neurons that integrate their function. Its effects within this system are diverse and site specific and are (at many levels) not well defined. However, most evidence suggests that the neuromodulator's influence acts to restrain sympathetic outflow and facilitate parasympathetic outflow. In chronic heart failure, these functional effects of NO are impaired or downregulated and contribute to the state of sympathetic overactivation and parasympathetic deactivation characterized by the disease. The cellular and molecular mechanisms regulating NO production and signaling in the autonomic nervous system in the normal and chronic heart failure state are summarized and discussed in light of their therapeutic implications. This review also emphasizes questions of regulation of NO function in the autonomic nervous system that remain unresolved.

Effects of insulin resistance on endothelial progenitor cells and vascular repair

Insulin resistance, a key feature of obesity, the metabolic syndrome and Type 2 diabetes mellitus, results in an array of metabolic and vascular phenomena which ultimately promote the development of atherosclerosis. Endothelial dysfunction is intricately related to insulin resistance through the parallel stimulatory effects of insulin on glucose disposal in metabolic tissues and NO production in the endothelium. Perturbations characteristic of insulin resistance, including dyslipidaemia, inflammation and oxidative stress, may jeopardize the structural or functional integrity of the endothelium. Recent evidence suggests that endothelial damage is mitigated by endogenous reparative processes which mediate endothelial regeneration. EPCs (endothelial progenitor cells) are circulating cells which have been identified as mediators of endothelial repair. Several of the abnormalities associated with insulin resistance, including reduced NO bioavailability, increased production of ROS (reactive oxygen species) and down-regulation of intracellular signalling pathways, have the potential to disrupt EPC function. Improvement in the number and function of EPCs may contribute to the protective actions of evidence-based therapies to reduce cardiometabolic risk. In the present article, we review the putative effects of insulin resistance on EPCs, discuss the underlying mechanisms and highlight potential therapeutic manoeuvres which could improve vascular repair in individuals with insulin resistance.

Estradiol increases guanosine 5'-triphosphate cyclohydrolase expression via the nitric oxide-mediated activation of cyclic adenosine 5'-monophosphate response element binding protein

A number of studies have demonstrated that estradiol can stimulate endothelial nitric oxide synthase expression and activity, resulting in enhanced nitric oxide (NO) generation. However, its effect on the NO synthase cofactor, tetrahydrobiopterin are less clear. Cellular tetrahydrobiopterin levels are regulated, at least in part, by GTP cyclohydrolase 1 (GCH1). Thus, the purpose of this study was to determine the effect of estradiol on GCH1 expression and the regulatory mechanisms in pulmonary arterial endothelial cells. Our data indicate that 17beta-estradiol (E2) increases GCH1 transcription in a dose- and time-dependent manner, whereas estrogen receptor antagonism or NO synthase inhibition attenuated E2-stimulated GCH1 expression. Analysis of the GCH1 promoter fragment responsive to E2 revealed the presence of a cAMP response element, and we found that E2 triggers a rapid but transient elevation of phospho-cAMP response element-binding protein (CREB; <1 h) followed by a second sustained rise after 6 h. EMSA analysis revealed an increase in the binding of CREB during E2 treatment and mutation of the cAMP response element in the GCH1 promoter attenuated the E2-mediated increase in transcription. Furthermore, inhibition of the cAMP-dependent kinase, protein kinase A (PKA) completely abolished the E2-stimulated GCH1 promoter activity, whereas the stimulation of cAMP levels with forskolin increased GCH1 promoter activity, indicating the key role of cAMP in regulating GCH1 promoter activity. In conclusion, our results demonstrate that estradiol can modulate GCH1 expression via NO-mediated activation of CREB in pulmonary arterial endothelial cells. These findings provide new insight into the vascular protective effect of estradiol.

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.

Disorders of biopterin metabolism

Defects in the metabolism or regeneration of tetrahydrobiopterin (BH4) were initially discovered in patients with hyperphenylalaninaemia who had progressive neurological deterioration despite optimal metabolic control (malignant hyperphenylalaninaemia). BH4 is an essential cofactor not only for phenylalanine hydroxylase, but also for tyrosine and two tryptophan hydroxylases, three nitric oxide synthases, and glyceryl-ether monooxygenase. Defective activity of tyrosine and tryptophan hydroxylases explains the neurological deterioration in patients with BH4 deficiency with progressive mental and physical retardation, central hypotonia and peripheral spasticity, seizures and microcephaly. Five separate genetic conditions affect BH4 synthesis or regeneration: deficiency of GTP cyclohydrolase I, 6-pyruvoyl tetrahydropterin synthase, sepiapterin reductase, dihydropteridine reductase (DHPR) and pterin-4alpha-carbinolamine dehydratase. Only the latter of these conditions is relatively benign and is associated with transient hyperphenylalaninaemia. All these conditions can be identified in newborns by an elevated phenylalanine, with the exception of sepiapterin reductase and the dominant form of GTP cyclohydrolase I deficiency that results in biopterin deficiency/insufficiency only in the brain. Diagnosis relies on the measurement of pterin metabolites in urine, dihydropteridine reductase in blood spots, neurotransmitters and pterins in the CSF and on the demonstration of reduced enzyme activity (red blood cells or fibroblasts) or causative mutations in the relative genes. The outcome of BH4 deficiency is no longer malignant if therapy is promptly initiated to reduce plasma phenylalanine levels and replace missing neurotransmitters. This is accomplished by a special diet and/or BH4 supplements and administration of L-dopa, carbidopa, 5-hydroxytryptophan, and, in certain cases, a MAO-B inhibitor. Patients with DHPR deficiency also require folinic acid supplements, since DHPR may help in maintaining folate in the tetrahydro form. Several patients with BH4 deficiency treated since the newborn period have reached adult age with good outcome.

L-arginine and tetrahydrobiopterin protects against ischemia/reperfusion-induced endothelial dysfunction in patients with type 2 diabetes mellitus and coronary artery disease

Diminished levels of L-arginine and endothelial nitric oxide synthase (eNOS) uncoupling through deficiency of tetrahydrobiopterin (BH(4)) may contribute to endothelial dysfunction. We investigated the effect of L-arginine and BH(4) administration on ischemia-reperfusion (I/R)-induced endothelial dysfunction in patients with type 2 diabetes and coronary artery disease (CAD). Forearm blood flow was measured by venous occlusion plethysmography in 12 patients with type 2 diabetes or impaired glucose tolerance and CAD. Forearm ischemia was induced for 20 min, followed by 60 min of reperfusion. The patients received a 15 min intra-brachial infusion of L-arginine (20 mg/min) and BH(4) (500 microg/min) or 0.9% saline starting at 15 min of ischemia on two separate study occasions. Compared with pre-ischemia the endothelium-dependent vasodilatation (EDV) induced by acetylcholine was significantly reduced at 15 and 30 min of reperfusion when saline was infused (P<0.001), but not following L-arginine and BH(4) infusion. EDV was also significantly less reduced at 15 and 30 min of reperfusion following L-arginine and BH(4) infusion, compared to saline infusion (P<0.02). Endothelium-independent vasodilatation (EIDV) induced by nitroprusside was unaffected by I/R. Venous total biopterin levels in the infused arm increased from 37+/-7 at baseline to 6644+/-1240 nmol/l during infusion of L-arginine and BH(4) (P<0.0001), whereas there was no difference in biopterin levels during saline infusion. In conclusion L-arginine and BH(4) supplementation reduces I/R-induced endothelial dysfunction, a finding which may represent a novel treatment strategy to limit I/R injury in patients with type 2 diabetes and CAD.

Production and Peripheral Roles of 5-HTP, a Precursor of Serotonin

Serotonin (5-hydroxytryptamine [5-HT]) has been implicated in a variety of physiological and pathological functions. Multiple steps of enzyme reactions enable biosynthesis of 5-HT. The first and rate-limiting step of the reaction is the synthesis of 5-hydroxy-L-tryptophan (5-HTP) from L-tryptophan. This step is dictated by an enzyme, tryptophan hydroxylase (TPH). TPH requires 6R-L-erythro-5,6,7,8-tetrahydrobiopterin (BH4) as a co-substrate of TPH. 5-HTP has been simply regarded as a precursor of 5-HT and it is believed that the biological significance of 5-HTP is essentially ascribed to the production of 5-HT. However, recent works shed light on the specific functions of 5-HTP in the periphery. In this review article, we focus on the specific roles of exogenous 5-HTP as well as the endogenous 5-HTP in the gut epithelial cells. Since systemic treatment with 5-HTP is applied to patients with lower 5-HT levels, the studies on the specific role of 5-HTP might create an opportunity to explore the effects of exogenously-applied 5-HTP in the gut in man.

The endothelial glycocalyx mediates shear-induced changes in hydraulic conductivity

Recent in vitro and in vivo studies have reported fluid shear stress-induced increases in endothelial layer hydraulic conductivity (L(p)) that are mediated by an increased production of nitric oxide (NO). Other recent studies have shown that NO induction by shear stress is mediated by the glycocalyx that decorates the surface of endothelial cells. Here we find that a selective depletion of the major components of the glycocalyx with enzymes can block the shear stress-induced response of L(p). Heparinase and hyaluronidase block shear-induced increases in L(p), which is consistent with their effects on NO production. But chondroitinase, which does not suppress shear-induced NO production, also inhibits shear-induced L(p). A further surprise is that treatment with the general proteolytic enzyme pronase does not suppress the shear L(p) response. We also find that heparinase does not alter baseline L(p) significantly, whereas chondroitinase, hyaluronidase, and pronase increase it significantly.

Vascular protection by tetrahydrobiopterin: progress and therapeutic prospects

Tetrahydrobiopterin (BH4) is an essential cofactor required for the activity of endothelial nitric oxide (NO) synthase. Suboptimal concentrations of BH4 in the endothelium reduce the biosynthesis of NO, thus contributing to the pathogenesis of vascular endothelial dysfunction. Supplementation with exogenous BH4 or therapeutic approaches that increase endogenous amounts of BH4 can reduce or reverse endothelial dysfunction by restoring production of NO. Improvements in formulations of BH4 for oral delivery have stimulated clinical trials that test the efficacy of BH4 in the treatment of systemic hypertension, peripheral arterial disease, coronary artery disease, pulmonary arterial hypertension, and sickle cell disease. This review discusses ongoing progress in the translation of knowledge, accumulated in preclinical studies, into the clinical application of BH4 in the treatment of vascular diseases. This review also addresses the emerging roles of BH4 in the regulation of endothelial function and their therapeutic implications.

Prostate-specific membrane antigen expression in regeneration and repair

Prostate-specific membrane antigen is a type II transmembrane glycoprotein, expressed in benign and neoplastic prostatic tissue as well as endothelial cells of neovasculature from a variety of tumors. The expression of prostate-specific membrane antigen in nonneoplastic neovasculature has not been well studied. Therefore, we studied nonneoplastic reparative and regenerative human tissues, as well as preneoplastic tissue, to determine the presence of prostate-specific membrane antigen-expressing neovasculature. Formalin-fixed paraffin-embedded tissue from keloids, granulation tissue from heart valves and pleura, proliferative and secretory endometrium, and Barrett's mucosa with and without dysplasia were stained for the expression of prostate-specific membrane antigen (3E6). Vessels of proliferative, mid-secretory, and late secretory endometrium were consistently strongly positive for prostate-specific membrane antigen expression in all ten cases of each type (100%). Vessels associated with granulation tissue from pleural peels and heart valves were positive in 10 of 12 cases (83%) and 7 of 10 cases (70%), respectively. Keloids had prostate-specific membrane antigen-expressing endothelial cells in 6 of 15 cases (40%). Prostate-specific membrane antigen was not expressed by vessels associated with Barrett's mucosa with low-grade dysplasia (12 foci), high-grade dysplasia (24 foci), or no dysplasia (18 foci). A variety of nonneoplastic neovasculature expresses prostate-specific membrane antigen, including vessels in proliferative endometrium, granulation tissue, and some scars. This is the first study showing that prostate-specific membrane antigen is expressed in neovasculature from physiologic regenerative and reparative conditions. The folate hydrolase activity of prostate-specific membrane antigen may facilitate vasculogenesis and angiogenesis by increasing local availability of folic acid. These findings will enhance our overall understanding of blood vessel development and will enable us to better understand the effects of anti-prostate-specific membrane antigen therapies, which are already being explored in clinical trials.

Redox control of endothelial function and dysfunction: molecular mechanisms and therapeutic opportunities

The endothelium is essential for the maintenance of vascular homeostasis. Central to this role is the production of endothelium-derived nitric oxide (EDNO), synthesized by the endothelial isoform of nitric oxide synthase (eNOS). Endothelial dysfunction, manifested as impaired EDNO bioactivity, is an important early event in the development of various vascular diseases, including hypertension, diabetes, and atherosclerosis. The degree of impairment of EDNO bioactivity is a determinant of future vascular complications. Accordingly, growing interest exists in defining the pathologic mechanisms involved. Considerable evidence supports a causal role for the enhanced production of reactive oxygen species (ROS) by vascular cells. ROS directly inactivate EDNO, act as cell-signaling molecules, and promote protein dysfunction, events that contribute to the initiation and progression of endothelial dysfunction. Increasing data indicate that strategies designed to limit vascular ROS production can restore endothelial function in humans with vascular complications. The purpose of this review is to outline the various ways in which ROS can influence endothelial function and dysfunction, describe the redox mechanisms involved, and discuss approaches for preventing endothelial dysfunction that may highlight future therapeutic opportunities in the treatment of cardiovascular disease.

Dysregulation of antioxidant mechanisms contributes to increased oxidative stress in calcific aortic valvular stenosis in humans

OBJECTIVES

The aim of this study was to determine whether oxidative stress is increased in calcified, stenotic aortic valves and to examine mechanisms that might contribute to increased oxidative stress.

BACKGROUND

Oxidative stress is increased in atherosclerotic lesions and might play an important role in plaque progression and calcification. The role of oxidative stress in valve disease is not clear.

METHODS

Superoxide (dihydroethidium fluorescence and lucigenin-enhanced chemiluminescence), hydrogen peroxide H2O2 (dichlorofluorescein fluorescence), and expression and activity of pro- and anti-oxidant enzymes were measured in normal valves from hearts not suitable for transplantation and stenotic aortic valves that were removed during surgical replacement of the valve.

RESULTS

In normal valves, superoxide levels were relatively low and distributed homogeneously throughout the valve. In stenotic valves, superoxide levels were increased 2-fold near the calcified regions of the valve (p < 0.05); noncalcified regions did not differ significantly from normal valves. Hydrogen peroxide levels were also markedly elevated in calcified regions of stenotic valves. Nicotinamide adenine dinucleotide phosphate oxidase activity was not increased in calcified regions of stenotic valves. Superoxide levels in stenotic valves were significantly reduced by inhibition of nitric oxide synthases (NOS), which suggests uncoupling of the enzyme. Antioxidant mechanisms were reduced in calcified regions of the aortic valve, because total superoxide dismutase (SOD) activity and expression of all 3 SOD isoforms was significantly decreased. Catalase expression also was reduced in pericalcific regions.

CONCLUSIONS

This study provides the first evidence that oxidative stress is increased in calcified regions of stenotic aortic valves from humans. Increased oxidative stress is due at least in part to reduction in expression and activity of antioxidant enzymes and perhaps to uncoupled NOS activity. Thus, mechanisms of oxidative stress differ greatly between stenotic aortic valves and atherosclerotic arteries.

Vascular endothelium in atherosclerosis

Their strategic location between blood and tissue and their constitutive properties allow endothelial cells (EC) to monitor the transport of plasma molecules, by employing bidirectional receptor-mediated and receptor-independent transcytosis and endocytosis, and to regulate vascular tone, cellular cholesterol and lipid homeostasis. These cells are also involved in signal transduction, immunity, inflammation and haemostasis. Cardiovascular risk factors, such as hyperlipaemia/dyslipidaemia trigger the molecular machinery of EC to respond to insults by modulation of their constitutive functions followed by dysfunction and ultimately by injury and apoptosis. The gradual activation of EC consists initially in the modulation of two constitutive functions: (1) permeability, i.e. increased transcytosis of lipoproteins, and (2) biosynthetic activity, i.e. enhanced synthesis of the basement membrane and extracellular matrix. The increased transcytosis and the reduced efflux of beta-lipoproteins (betaLp) lead to their retention within the endothelial hyperplasic basal lamina as modified lipoproteins (MLp) and to their subsequent alteration (oxidation, glycation, enzymatic modifications). MLp generate chemoattractant and inflammatory molecules, triggering EC dysfunction (appearance of new adhesion molecules, secretion of chemokines, cytokines), characterised by monocyte recruitment, adhesion, diapedesis and residence within the subendothelium. In time, EC in the athero-prone areas alter their net negative surface charge, losing their non-thrombogenic ability, become loaded with lipid droplets and turn into foam cells. Prolonged and/or repeated exposure to cardiovascular risk factors can ultimately exhaust the protective effect of the endogenous anti-inflammatory system within EC. As a consequence, EC may progress to senescence, lose their integrity and detach into the circulation.

Systematic evaluation of nitric oxide, tetrahydrobiopterin, and anandamide levels in a porcine model of endotoxemia

PURPOSE

Using a lipopolysaccharide (LPS)-treated porcine model, we examined: (1) whether nitric oxide (NO), anandamide, and tetrahydrobiopterin (BH4) increased or not in early endotoxic shock; and (2) the location of the major site of production of these molecules, by comparing their concentrations in arteries and the portal and hepatic veins.

METHODS

Ten pigs received an infusion of LPS at 1.7 microg x kg(-1)x h(-1) via the portal vein for 240 min. Consecutive changes in systemic hemodynamics, hepatosplanchnic circulation, and oxygen delivery were measured. Furthermore, the variable changes in the concentrations of nitrite and nitrate (NOx), anandamide, and BH4 were measured. To access the effects of surgery, anesthesia, and fluid management on BH4, an experiment without LPS infusion was performed in two other animals.

RESULTS

Mean arterial pressure and cardiac index started to decrease at 60 min after LPS infusion. However, systemic vascular resistance remained unchanged. Total hepatic blood flow and hepatic oxygen delivery also decreased significantly. NOx and anandamide did not change during LPS infusion. BH4 values did not change without LPS infusion. However, BH4 values increased significantly in the arterial, portal, and hepatic circulation during LPS infusion, especially in the hepatic vein (from 136.8 +/- 27.5 to 281.3 +/- 123.2 mol/ml; P < 0.01).

CONCLUSION

Our data suggest that the BH4 values were significantly increased in several organs, especially in the liver during endotoxic shock. Impaired cardiac output and decreased blood pressure appeared in the early phase of porcine endotoxemia. Longer-term observation of these parameters after LPS treatment should be performed as the next step in future studies.

Cellular uptake of sepiapterin and push-pull accumulation of tetrahydrobiopterin

Cellular uptake of sepiapterin resulted in an efficient accumulation of tetrahydrobiopterin. Tetrahydrobiopterin is much less permeable across the cell membrane than sepiapterin or dihydrobiopterin, the precursors of the tetrahydrobiopterin-salvage pathway. The uptake of sepiapterin by the cell was examined under metabolic arrest with N-acetylserotonin, an inhibitor of sepiapterin reductase. The release profile of previously accumulated sepiapterin was also analyzed. Two routes were clearly distinguishable, namely rapid and slow. Both were apparently bi-directional and equilibrating in type. Each route was connected to non-mixable pools somehow separated in the cell. The rapid process was too fast to analyze by the current methods of cell handling. The slower process was associated with conversion of sepiapterin to tetrahydrobiopterin in the absence of N-acetylserotonin, suggesting that this route opens into the cytosolic compartment where use of the salvage pathway was strongly driven by sepiapterin reductase and dihydrofolate reductase with a supply of NADPH which favors tetrahydrobiopterin accumulation. Consequently, sepiapterin was enforcedly taken up by the cell where it accumulated tetrahydrobiopterin in the cytosol in continuous manner.

Nitric oxide, tetrahydrobiopterin, oxidative stress, and endothelial dysfunction in hypertension

Endothelial dysfunction in the setting of cardiovascular risk factors such as hypercholesterolemia, diabetes mellitus, chronic smoking, as well hypertension, is, at least in part, dependent of the production of reactive oxygen species (ROS) and the subsequent decrease in vascular bioavailability of nitric oxide (NO). ROS-producing enzymes involved in increased oxidative stress within vascular tissue include NADPH oxidase, xanthine oxidase, and mitochondrial superoxide producing enzymes. Superoxide produced by the NADPH oxidase may react with NO, thereby stimulating the production of the NO/superoxide reaction product peroxynitrite. Peroxynitrite in turn has been shown to uncouple eNOS, therefore switching an antiatherosclerotic NO producing enzyme to an enzyme that may accelerate the atherosclerotic process by producing superoxide. Increased oxidative stress in the vasculature, however, is not restricted to the endothelium and also occurs within the smooth muscle cell layer. Increased superoxide production has important consequences with respect to signaling by the soluble guanylate cyclase and the cGMP-dependent kinase I, which activity and expression is regulated in a redox-sensitive fashion. The present review will summarize current concepts concerning eNOS uncoupling, with special focus on the role of tetrahydrobiopterin in mediating eNOS uncoupling.

Sickle cell disease vasculopathy: a state of nitric oxide resistance

Sickle cell disease (SCD) is a hereditary hemoglobinopathy characterized by microvascular vaso-occlusion with erythrocytes containing polymerized sickle (S) hemoglobin, erythrocyte hemolysis, vasculopathy, and both acute and chronic multiorgan injury. It is associated with steady state increases in plasma cell-free hemoglobin and overproduction of reactive oxygen species (ROS). Hereditary and acquired hemolytic conditions release into plasma hemoglobin and other erythrocyte components that scavenge endothelium-derived NO and metabolize its precursor arginine, impairing NO homeostasis. Overproduction of ROS, such as superoxide, by enzymatic (xanthine oxidase, NADPH oxidase, uncoupled eNOS) and nonenzymatic pathways (Fenton chemistry), promotes intravascular oxidant stress that can likewise disrupt NO homeostasis. The synergistic bioinactivation of NO by dioxygenation and oxidation reactions with cell-free plasma hemoglobin and ROS, respectively, is discussed as a mechanism for NO resistance in SCD vasculopathy. Human physiological and transgenic animal studies provide experimental evidence of cardiovascular and pulmonary resistance to NO donors and reduced NO bioavailability that is associated with vasoconstriction, decreased blood flow, platelet activation, increased endothelin-1 expression, and end-organ injury. Emerging epidemiological data now suggest that chronic intravascular hemolysis is associated with certain clinical complications: pulmonary hypertension, cutaneous leg ulcerations, priapism, and possibly stroke. New therapeutic strategies to limit intravascular hemolysis and ROS generation and increase NO bioavailability are discussed.

Ratio of 5,6,7,8-tetrahydrobiopterin to 7,8-dihydrobiopterin in endothelial cells determines glucose-elicited changes in NO vs. superoxide production by eNOS

5,6,7,8-Tetrahydrobiopterin (BH(4)) is an essential cofactor of nitric oxide synthases (NOSs). Oxidation of BH(4), in the setting of diabetes and other chronic vasoinflammatory conditions, can cause cofactor insufficiency and uncoupling of endothelial NOS (eNOS), manifest by a switch from nitric oxide (NO) to superoxide production. Here we tested the hypothesis that eNOS uncoupling is not simply a consequence of BH(4) insufficiency, but rather results from a diminished ratio of BH(4) vs. its catalytically incompetent oxidation product, 7,8-dihydrobiopterin (BH(2)). In support of this hypothesis, [(3)H]BH(4) binding studies revealed that BH(4) and BH(2) bind eNOS with equal affinity (K(d) approximately 80 nM) and BH(2) can rapidly and efficiently replace BH(4) in preformed eNOS-BH(4) complexes. Whereas the total biopterin pool of murine endothelial cells (ECs) was unaffected by 48-h exposure to diabetic glucose levels (30 mM), BH(2) levels increased from undetectable to 40% of total biopterin. This BH(2) accumulation was associated with diminished calcium ionophore-evoked NO activity and accelerated superoxide production. Since superoxide production was suppressed by NOS inhibitor treatment, eNOS was implicated as a principal superoxide source. Importantly, BH(4) supplementation of ECs (in low and high glucose-containing media) revealed that calcium ionophore-evoked NO bioactivity correlates with intracellular BH(4):BH(2) and not absolute intracellular levels of BH(4). Reciprocally, superoxide production was found to negatively correlate with intracellular BH(4):BH(2). Hyperglycemia-associated BH(4) oxidation and NO insufficiency was recapitulated in vivo, in the Zucker diabetic fatty rat model of type 2 diabetes. Together, these findings implicate diminished intracellular BH(4):BH(2), rather than BH(4) depletion per se, as the molecular trigger for NO insufficiency in diabetes.

Antiatherosclerotic effects of small-molecular-weight compounds enhancing endothelial nitric-oxide synthase (eNOS) expression and preventing eNOS uncoupling

Many cardiovascular diseases are associated with reduced levels of bioactive nitric oxide (NO) and an uncoupling of oxygen reduction from NO synthesis in endothelial NO synthase (eNOS uncoupling). In human endothelial EA.hy 926 cells, two small-molecular-weight compounds with related structures, 4-fluoro-N-indan-2-yl-benzamide (CAS no. 291756-32-6; empirical formula C16H14FNO; AVE9488) and 2,2-difluoro-benzo[1,3]dioxole-5-carboxylic acid indan-2-ylamide (CAS no. 450348-85-3; empirical formula C17H13F2NO3; AVE3085), enhanced eNOS promoter activity in a concentration-dependent manner; with the responsible cis-element localized within the proximal 263 base pairs of the promoter region. RNA interference-mediated knockdown of the transcription factor Sp1 significantly reduced the basal activity of eNOS promoter, but it did not prevent the transcription activation by the compounds. Enhanced transcription of eNOS by AVE9488 in primary human umbilical vein endothelial cells was associated with increased levels of eNOS mRNA and protein expression, as well as increased bradykinin-stimulated NO production. In both wild-type C57BL/6J mice and apolipoprotein E-knockout (apoE-KO) mice, treatment with AVE9488 resulted in enhanced vascular eNOS expression. In apoE-KO mice, but not in eNOS-knockout mice, treatment with AVE9488 reduced cuff-induced neointima formation. A 12-week treatment with AVE9488 or AVE3085 reduced atherosclerotic plaque formation in apoE-KO mice, but not in apoE/eNOS-double knockout mice. Aortas from apoE-KO mice showed a significant generation of reactive oxygen species. This was partly prevented by nitric-oxide inhibitor N(omega)-nitro-l-arginine methyl ester, indicating eNOS uncoupling. Treatment of mice with AVE9488 enhanced vascular content of the essential eNOS cofactor (6R)-5,6,7,8-tetrahydro-l-biopterin and reversed eNOS uncoupling. The combination of an up-regulated eNOS expression and a reversal of eNOS uncoupling is probably responsible for the observed vasoprotective properties of this new type of compounds.

Tetrahydrobiopterin

The endothelium plays a pivotal role in vascular physiology through a variety of factors, foremost of which is nitric oxide (NO). However, the biochemical mechanisms leading to reduced NO availability and subsequent endothelial dysfunction are not clearly understood. Tetrahydrobiopterin (BH(4)) is an essential cofactor for endothelial NO synthase. Recent preclinical and clinical studies in patients with cardiovascular risk and disease support the central role of reduced BH(4) availability in decreased NO production. This has led to BH(4) supplementation emerging as a possible therapy for conditions characterized by endothelial dysfunction (eg, hypertension, hypercholesterolemia, diabetes, and vascular disease states), and those caused by smoking and aging. Recent advances in drug formulation of BH(4) now offer the potential for better clinical understanding of endothelial function in human health and disease.

Transiently, paralleled upregulation of arginase and nitric oxide synthase and the effect of both enzymes on the pathology of asthma

Changes in the expression of arginase and their association with nitrosative stress were investigated using an asthmatic model previously established in NC/Nga mice with mite extract. Mite crude extract (100 microg/day) from Dermatophagoides farinae was administered intranasally for 5 consecutive days (day 0-4), and a single challenge was performed on day 11. On day 12, upregulation of the mRNA expression of inducible types of nitric oxide synthase (iNOS) and increases in immunohistochemical staining for iNOS and nitrotyrosine were observed. However, the level of nitrite + nitrate was unchanged. An increase in enzymatic activity, upregulation of mRNA expression, and immunostaining for arginase I was detected in the lung tissue and serum. Moreover, increases in both arginase I and II were revealed by immunoblotting. Goblet cell hyperplasia in bronchial epithelial cells and increasing collagen synthesis around the bronchus were also observed. These results suggested that an increase in arginase may lead to decreased availability of arginine for nitric oxide synthase and may contribute to the remodeling of the lung.