Hydrogen peroxide stimulates tetrahydrobiopterin synthesis through the induction of GTP-cyclohydrolase I and increases nitric oxide synthase activity in vascular endothelial cells

Changes in FeNO, d-ROMs, and BH4 by Intravenous L-Arginine in Children and Its Putative Role in Asthma Treatment

Purpose

Pteridines are metabolites of tetrahydrobiopterin (BH4), being coenzymes for nitric oxide synthase (NOS). No study has clarified the relationship among pteridines and NOS, fractional exhaled nitric oxide (FeNO) generated by pteridines, and reactive oxygen species. In this study, we administered arginine, a precursor of NO, and confirmed changes in the levels of pteridines, FeNO, and reactive oxygen species and their relationship to clarify the pathogenesis of airway inflammation in which oxidative stress is involved, such as bronchial asthma.

Patients and Methods

This is a prospective, randomized open-label study. Children, aged 2 to 15 years, who were scheduled for growth hormone stimulation tests and were able to undergo a respiratory function test were recruited. They were randomly divided into two groups: arginine-administered and control groups. In the former, L-arginine hydrochloride was intravenously administered. After administration, the levels of diacron-reactive oxygen metabolites (d-ROMs), serum pteridines, serum amino acids, and fractional exhaled NO (FeNO) were measured.

Results

We analyzed 15 children aged 4 to 14 years. In the arginine-administered group, there was an increase in the FeNO level and a decrease in the d-ROMs level, reaching a peak 30 min after administration, compared with the control group. In addition, there was a decrease in the serum biopterin level and an increase in the d-ROMs level, reaching peak 60 min after administration.

Conclusion

The administration of L-arginine increased the NO level and decreased the d-ROMs level. Due to this, biopterin may be consumed and decreased, leading to an increase in the d-ROMs level. As a reduction in reactive oxygen species leads to the relief of inflammation, arginine and biopterin may be useful for inhibiting inflammation.

Pterin metabolism, inflammation and oxidative stress biochemical markers in schizophrenia: Factor analysis and assessment of clinical symptoms associations

Various aspects of folate and tetrahydrobiopterin (BH4) metabolism disturbances have been detected in patients with schizophrenia.Data were obtained that disturbances in the pterins (folates and BH4) metabolism can be associated with oxidative stress and inflammation, but has not yet been confirmed in clinical studies in schizophrenia. Within the framework of this study, a correlation and factor analysis of biochemical markersof pterin metabolism, inflammation and redox imbalance in patients with schizophrenia was performed in order to test the hypothesis of the single etiopathogenetic node, including the studied biochemical processes. Methods: 125 patients with schizophrenia and 95 healthy volunteers were randomly selected and evaluated with a biochemical examination of BH4, folate, B12, homocysteine, C-reactive protein, interleukin-6, reduced glutathione levels in the blood serum; activity of superoxide dismutase and catalase - in erythrocytes; malondialdehyde - in blood plasma. All patients underwent an examination using standardized psychopathology rating scales. Spearman rank coefficient (ρ) with Benjamini-Hochberg correction was used for the correlation analysis. The principal components analysis (PCA) was used as a factor analysis. Results: Significant correlations were found within groups of pterin metabolism, inflammatory markers and redox-imbalance, and also between separate inflammation, oxidative stress and markers of pterin metabolism. The performed factor analysis made it possible to distinguish two components: 1 - pterin metabolism, 2 - oxidativeinflammatory markers. Despite the weak statistical associations and, possibly, functional relationships between pterin metabolism and oxidative/inflammation markers, each of the components has its own clinical correlates and, probably, a separate contribution to the pathology of schizophrenia.

NADPH oxidases in the differentiation of endothelial cells

The differentiation of stem cells into endothelial cells involves the modulation of highly interconnected metabolic and epigenetic processes. Therefore, the differentiation of endothelial cells is a tightly controlled process, which is adjusted at multiple levels, meaning that even the smallest variation can result in major consequences. Reactive oxygen species (ROS) represent a group of second messengers that can interfere with both metabolic and epigenetic processes. Besides their generation by mitochondria, ROS are produced in a controlled manner by the family of NADPH oxidases. The different members of the NADPH oxidase family produce superoxide anions or hydrogen peroxide. Due to the specific sub-cellular localization of the different NADPH oxidases, ROS are produced at diverse sites in the cell, such as the plasma membrane or the endoplasmic reticulum. Once produced, ROS interfere with proteins, lipids, and DNA to modulate intracellular signal cascades. Accordingly, ROS represent a group of readily available and specifically localized modulators of the highly sophisticated signalling network that eventually leads to the differentiation of stem cells into endothelial cells. This review focuses on the role of NADPH oxidases in the differentiation of stem cells into endothelial cells.

Labour analgesia; Molecular pathway and the role of nanocarriers: a systematic review

Labour is considered to be one of the most painful procedures in human experience. The most effective technique for pain relief during labour is neuraxial labour analgesia which provides analgesia without maternal or fetal sedation. Genetic predisposition may be of importance for pain perception and women experience varying degrees of pain in labour. Genetic variations in opioid receptor (OPR) genes may influence the response to epidural opioid analgesia during labour. The single-nucleotide polymorphism, A118G of the mu opioid receptor gene (oprm1), has been associated with altered pain perception. Targeted drug delivery reduces toxic side effects. Liposomes, nano-particles, nanofibres hydrogel, have been suggested to deliver anaesthetic drugs.

Roles for endothelial cell and macrophage Gch1 and tetrahydrobiopterin in atherosclerosis progression

Aims

GTP cyclohydrolase I catalyses the first and rate-limiting reaction in the synthesis of tetrahydrobiopterin (BH4), an essential cofactor for nitric oxide synthases (NOS). Both eNOS and iNOS have been implicated in the progression of atherosclerosis, with opposing effects in eNOS and iNOS knockout mice. However, the pathophysiologic requirement for BH4 in regulating both eNOS and iNOS function, and the effects of loss of BH4 on the progression of atherosclerosis remains unknown.

Methods and results

Hyperlipidemic mice deficient in Gch1 in endothelial cells and leucocytes were generated by crossing Gch1fl/flTie2cre mice with ApoE-/- mice. Deficiency of Gch1 and BH4 in endothelial cells and myeloid cells was associated with mildly increased blood pressure. High fat feeding for 6 weeks in Gch1fl/flTie2CreApoE-/- mice resulted in significantly decreased circulating BH4 levels, increased atherosclerosis burden and increased plaque macrophage content. Gch1fl/flTie2CreApoE-/- mice showed hallmarks of endothelial cell dysfunction, with increased aortic VCAM-1 expression and decreased endothelial cell dependent vasodilation. Furthermore, loss of BH4 from pro-inflammatory macrophages resulted in increased foam cell formation and altered cellular redox signalling, with decreased expression of antioxidant genes and increased reactive oxygen species. Bone marrow chimeras revealed that loss of Gch1 in both endothelial cells and leucocytes is required to accelerate atherosclerosis.

Conclusion

Both endothelial cell and macrophage BH4 play important roles in the regulation of NOS function and cellular redox signalling in atherosclerosis.

Possible involvement of tetrahydrobiopterin in the disturbance of redox homeostasis in sepsis - Induced brain dysfunction

BACKGROUND AND AIM

Tetrahydrobiopterin (BH4) is an essential co-factor that regulates nitric oxide (NO) and reactive oxygen species (ROS) production by nitric oxide synthases (NOS). In this study, we evaluated the effects of sepsis on BH4 level and redox status in the brain by using the rat model of sepsis-induced by cecal ligation and puncture (CLP) and examined whether BH4 and/or acetyl-L-carnitine (ALC) could prevent the neuronal apoptosis and neurological changes induced by sepsis.

MATERIAL AND METHOD

Male albino rats were randomly and blindly divided into 8 groups: sham, sham + BH4, sham + ALC, sham +BH4+ ALC, CLP, CLP + BH4, CLP + ALC, and CLP+BH4+ ALC. We measured neurological indicators, brain levels of BH4, guanosine triphosphate cyclohydrolase (GTPCH), sepiapterin reductase (SR) and dihydropteridine reductase (DHPR) genes expression (Essential enzymes in BH4 biosynthesis and recycling pathways). We investigated also brain redox status and both endothelial and inducible NOS expressions.

RESULTS

Brain of septic rats demonstrated a reduced BH4 bioavailability, downregulation of BH4 synthetic enzymes, increased production of hydrogen peroxide and impaired antioxidant enzymes activities. Treatments with BH4 and/or ALC increased BH4 level, upregulated BH4 synthetic enzymes expressions, and attenuated oxidative-induced neuronal apoptosis.

CONCLUSION

Our results suggest that BH4 and/or ALC might protect the brain against oxidative stress induced neuronal apoptosis by restoring bioavailability of BH4 and upregulating of BH4 synthetic enzymes in the brain during sepsis.

Computational analysis of interactions of oxidative stress and tetrahydrobiopterin reveals instability in eNOS coupling

In cardiovascular and neurovascular diseases, an increase in oxidative stress and endothelial dysfunction has been reported. There is a reduction in tetrahydrobiopterin (BH4), which is a cofactor for the endothelial nitric oxide synthase (eNOS), resulting in eNOS uncoupling. Studies of the enhancement of BH4 availability have reported mixed results for improvement in endothelial dysfunction. Our understanding of the complex interactions of eNOS uncoupling, oxidative stress and BH4 availability is not complete and a quantitative understanding of these interactions is required. In the present study, we developed a computational model for eNOS uncoupling that considers the temporal changes in biopterin ratio in the oxidative stress conditions. Using the model, we studied the effects of cellular oxidative stress (Qsupcell) representing the non-eNOS based oxidative stress sources and BH4 synthesis (QBH4) on eNOS NO production and biopterin ratio (BH4/total biopterins (TBP)). Model results showed that oxidative stress levels from 0.01 to 1nM·s-1 did not affect eNOS NO production and eNOS remained in coupled state. When the Qsupcell increased above 1nM·s-1, the eNOS coupling and NO production transitioned to an oscillatory state. Oxidative stress levels dynamically changed the biopterin ratio. When Qsupcell increased from 1 to 100nM·s-1, the endothelial cell NO production, TBP levels and biopterin ratio reduced significantly from 26.5 to 2nM·s-1, 3.75 to 0.002μM and 0.99 to 0.25, respectively. For an increase in BH4 synthesis, the improvement in NO production rate and BH4 levels were dependent on the extent of cellular oxidative stress. However, a 10-fold increase in QBH4 at higher oxidative stresses did not restore the NO-production rate and the biopterin ratio. Our mechanistic analysis reveals that a combination of enhancing tetrahydrobiopterin level with a reduction in cellular oxidative stress may result in significant improvement in endothelial dysfunction.

Environmental contributors to modulation of brain estrogen signaling and male gender bias in autism: A reply to the oral contraceptive use hypothesis by Strifert (2015)

Strifert has recently put forward an interesting hypothesis regarding the role of oral contraceptive (OC) use in mothers and risk of offspring autism spectrum disorder (ASD). First, the author reports that combined oral contraceptives (COCs), containing both estrogen and progesterone, were developed in the late 1950s and early 60s, which is a time-frame distinct from Leo Kanner's documentation of infantile ASD in 1943 that Strifert just briefly mentions. While this important temporal inconsistency of ASD origin does not invalidate the potential role of OC use in contributing to the rise of ASD, it does support the likely possibility of other environmental exposures at play. Second, the epigenetic basis of the hypothesis is that the endocrine-disrupting components (i.e., ethinylestradiol) of OC perturb estrogenic signaling in the fetal brain by triggering aberrant DNA methylation of the estrogen receptor β (ERβ) gene, and such methylation patterns may be imprinted to future generations and could theoretically increase subsequent ASD offspring risk. The premise of the hypothesis is challenged, however, with the recognition that MeCP2, a "reader" of DNA methylation sites, is not only associated with age-dependent alteration in ERβ in females but is also significantly reduced in ASD brain. Furthermore, Strifert does not clearly address how the OC hypothesis accounts for the male bias in ASD. Therefore, the purpose of this correspondence is to address these inconsistencies by proposing a hypothesis that challenges these points. That is, gestational exposure to the agricultural and combustion air pollutant, nitrous oxide (N₂O), may be a leading contributor to the development of an ASD phenotype. The mechanism undergirding this hypothesis suggests that compensatory estrogenic activity may mitigate the effects of fetal N₂O exposure and thereby confer a protective effect against ASD development in a sex-dependent manner (i.e., male bias in ASD).

Anesthetic agents, neurodevelopmental risk and the connection to bacterial infections

This short communication identifies a significant flaw in research investigating the neurodevelopmental consequences of general anesthesia exposure. We have identified that chronic environmental exposure to pervasive air pollutants that are also widely used as anesthetic agents, specifically nitrous oxide (N₂O), may contribute to the rising prevalence of neurodevelopmental disorders. Consistent with the emerging link between microbes and psychiatric illness risk, this epidemiological analysis extends our prior conclusions by proposing that such exposures may alter host immunity so as to enhance vulnerability to certain pathogenic microbes that have been implicated in neurodevelopmental disorders, including Pseudomonas aeruginosa and Clostridium difficile.

Co-administration of α-lipoic acid and cyclosporine aggravates colon ulceration of acetic acid-induced ulcerative colitis via facilitation of NO/COX-2/miR-210 cascade

In this work, α-lipoic acid and cyclosporine demonstrated significant protection against acetic acid-induced ulcerative colitis in rats. We proposed that α-lipoic acid and cyclosporine co-administration might modulate their individual effects. Induction of ulcerative colitis in rats was performed by intra-rectal acetic acid (5% v/v) administration for 3 consecutive days. Effects of individual or combined used of α-lipoic acid (35 mg/kg ip) or cyclosporine (5mg/kg sc) for 6 days starting 2 days prior to acetic acid were assessed. Acetic acid caused colon ulceration, bloody diarrhea and weight loss. Histologically, there was mucosal atrophy and inflammatory cells infiltration in submucosa, associated with depletion of colon reduced glutathione, superoxide dismutase and catalase activities and elevated colon malondialdehyde, serum C-reactive protein (C-RP) and tumor necrosis factor-α (TNF-α). Colon gene expression of cyclooxygenase-2 and miR-210 was also elevated. These devastating effects of acetic acid were abolished upon concurrent administration of α-lipoic acid. Alternatively, cyclosporine caused partial protection against acetic acid-induced ulcerative colitis. Cyclosporine did not restore colon reduced glutathione, catalase activity, serum C-RP or TNF-α. Unexpectedly, co-administration of α-lipoic acid and cyclosporine aggravated colon ulceration. Concomitant use of α-lipoic acid and cyclosporine significantly increased nitric oxide production, cyclooxygenase-2 and miR-210 gene expression compared to all other studied groups. The current findings suggest that facilitation of nitric oxide/cyclooxygenase-2/miR-210 cascade constitutes, at least partially, the cellular mechanism by which concurrent use of α-lipoic acid and cyclosporine aggravates colon damage. Collectively, the present work highlights the probable risk of using α-lipoic acid/cyclosporine combination in ulcerative colitis patients.

Basal brain oxidative and nitrative stress levels are finely regulated by the interplay between superoxide dismutase 2 and p53

Superoxide dismutases (SODs) are the primary reactive oxygen species (ROS)-scavenging enzymes of the cell and catalyze the dismutation of superoxide radicals O2- to H2O2 and molecular oxygen (O2). Among the three forms of SOD identified, manganese-containing SOD (MnSOD, SOD2) is a homotetramer located wholly in the mitochondrial matrix. Because of the SOD2 strategic location, it represents the first mechanism of defense against the augmentation of ROS/reactive nitrogen species levels in the mitochondria for preventing further damage. This study seeks to understand the effects that the partial lack (SOD2(-/+) ) or the overexpression (TgSOD2) of MnSOD produces on oxidative/nitrative stress basal levels in different brain isolated cellular fractions (i.e., mitochondrial, nuclear, cytosolic) as well as in the whole-brain homogenate. Furthermore, because of the known interaction between SOD2 and p53 protein, this study seeks to clarify the impact that the double mutation has on oxidative/nitrative stress levels in the brain of mice carrying the double mutation (p53(-/-) × SOD2(-/+) and p53(-/-) × TgSOD2). We show that each mutation affects mitochondrial, nuclear, and cytosolic oxidative/nitrative stress basal levels differently, but, overall, no change or reduction of oxidative/nitrative stress levels was found in the whole-brain homogenate. The analysis of well-known antioxidant systems such as thioredoxin-1 and Nrf2/HO-1/BVR-A suggests their potential role in the maintenance of the cellular redox homeostasis in the presence of changes of SOD2 and/or p53 protein levels.

Tetrahydrobiopterin in cardiovascular health and disease

Tetrahydrobiopterin (BH4) functions as a cofactor for several important enzyme systems, and considerable evidence implicates BH4 as a key regulator of endothelial nitric oxide synthase (eNOS) in the setting of cardiovascular health and disease. BH4 bioavailability is determined by a balance of enzymatic de novo synthesis and recycling, versus degradation in the setting of oxidative stress. Augmenting vascular BH4 levels by pharmacological supplementation has been shown in experimental studies to enhance NO bioavailability. However, it has become more apparent that the role of BH4 in other enzymatic pathways, including other NOS isoforms and the aromatic amino acid hydroxylases, may have a bearing on important aspects of vascular homeostasis, inflammation, and cardiac function. This article reviews the role of BH4 in cardiovascular development and homeostasis, as well as in pathophysiological processes such as endothelial and vascular dysfunction, atherosclerosis, inflammation, and cardiac hypertrophy. We discuss the therapeutic potential of BH4 in cardiovascular disease states and attempt to address how this modulator of intracellular NO-redox balance may ultimately provide a powerful new treatment for many cardiovascular diseases.

Mechanisms of vascular dysfunction in mice with endothelium-specific deletion of the PPAR-δ gene

Peroxisome proliferator-activated receptor (PPAR)-δ is a nuclear hormone receptor that is mainly involved in lipid metabolism. Recent studies have suggested that PPAR-δ agonists exert vascular protective effects. The present study was designed to characterize vascular function in mice with genetic inactivation of PPAR-δ in the endothelium. Mice with vascular endothelial cell-specific deletion of the PPAR-δ gene (ePPARδ(-/-) mice) were generated using loxP/Cre technology. ePPARδ(-/-) mice were normotensive and did not display any sign of metabolic syndrome. Endothelium-dependent relaxations to ACh and endothelium-independent relaxations to the nitric oxide (NO) donor diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate were both significantly impaired in the aorta and carotid arteries of ePPARδ(-/-) mice (P < 0.05). In ePPARδ(-/-) mouse aortas, phosphorylation of endothelial NO synthase at Ser(1177) was significantly decreased (P < 0.05). However, basal levels of cGMP were unexpectedly increased (P < 0.05). Enzymatic activity of GTP-cyclohydrolase I and tetrahydrobiopterin levels were also enhanced in ePPARδ(-/-) mice (P < 0.05). Most notably, endothelium-specific deletion of the PPAR-δ gene significantly decreased protein expressions of catalase and glutathione peroxidase 1 and resulted in increased levels of H2O2 in the aorta (P < 0.05). In contrast, superoxide anion production was unaltered. Moreover, treatment with catalase prevented the endothelial dysfunction and elevation of cGMP detected in aortas of ePPARδ(-/-) mice. The findings suggest that increased levels of cGMP caused by H2O2 impair vasodilator reactivity to endogenous and exogenous NO. We speculate that chronic elevation of H2O2 predisposes PPAR-δ-deficient arteries to oxidative stress and vascular dysfunction.

Nitric oxide synthases in heart failure

SIGNIFICANCE

The regulation of myocardial function by constitutive nitric oxide synthases (NOS) is important for the maintenance of myocardial Ca(2+) homeostasis, relaxation and distensibility, and protection from arrhythmia and abnormal stress stimuli. However, sustained insults such as diabetes, hypertension, hemodynamic overload, and atrial fibrillation lead to dysfunctional NOS activity with superoxide produced instead of NO and worse pathophysiology.

RECENT ADVANCES

Major strides in understanding the role of normal and abnormal constitutive NOS in the heart have revealed molecular targets by which NO modulates myocyte function and morphology, the role and nature of post-translational modifications of NOS, and factors controlling nitroso-redox balance. Localized and differential signaling from NOS1 (neuronal) versus NOS3 (endothelial) isoforms are being identified, as are methods to restore NOS function in heart disease.

CRITICAL ISSUES

Abnormal NOS signaling plays a key role in many cardiac disorders, while targeted modulation may potentially reverse this pathogenic source of oxidative stress.

FUTURE DIRECTIONS

Improvements in the clinical translation of potent modulators of NOS function/dysfunction may ultimately provide a powerful new treatment for many hearts diseases that are fueled by nitroso-redox imbalance.

Decreased cardiac mitochondrial tetrahydrobiopterin in a rat model of pressure overload

Sustained cardiac pressure overload induces mitochondrial dysfunction and apoptosis of cardiomyocytes leading to pathological cardiac hypertrophy and dysfunction. Mitochondrial nitric oxide synthase (NOS) appears to cause uncoupling, which produces reactive oxygen species (ROS) instead of nitric oxide (NO), by a decrease in the cofactor tetrahydrobiopterin (BH4). This study focused on examining the changes in mitochondrial BH4 levels during cardiac pressure overload. Chronic cardiac pressure overload was generated by abdominal aortic banding in rats. Levels of BH4 and its oxidized form were measured in the mitochondria isolated from the left ventricle (LV) and the post-mitochondrial supernatants. Chronic aortic banding increased blood pressure, and induced cardiac hypertrophy and fibrosis. Notably, the BH4 levels were decreased while its oxidized forms were increased in LV mitochondria, but not in the post-mitochondrial supernatants containing the cytosol and microsome. Anti-neuronal NOS antibody-sensitive protein was detected in the cardiac mitochondria. Moreover, continuous administration of BH4 to rats with pressure overload increased mitochondrial BH4 levels and reduced cardiac fibrosis and matrix metallopeptidase activity, but not cardiac hypertrophy. These findings show the possibility that NOS uncoupling by decreased cardiac mitochondrial BH4 levels is implicated, at least in part, in the development of cardiac fibrosis, leading to cardiac dysfunction induced by pressure overload.

The role of tetrahydrobiopterin in inflammation and cardiovascular disease

The cofactor tetrahydrobiopterin (BH4) is required for nitric oxide (NO) production by all nitric oxide synthase (NOS) enzymes and is a key regulator of cellular redox signalling. When BH4 levels become limiting NOS enzymes become 'uncoupled' and produce superoxide rather than NO. Endothelial cell BH4 is required for the maintenance of vascular function through NO production, and reduced BH4 levels are associated with vascular dysfunction. Evidence increasingly points to important roles for BH4 and NOS enzymes in other vascular cell types. Leukocytes have a fundamental role in atherosclerosis, and new evidence points to a role in the control of hypertension. Leukocytes are a major site of iNOS expression, and the regulation of this isoform is another mechanism by which BH4 availability may modulate disease. This review provides an overview of BH4 control of NOS function in both endothelial cells and leukocytes in the context of vascular disease and current therapeutic evaluations.

Apocynin improves oxygenation and increases eNOS in persistent pulmonary hypertension of the newborn

NADPH oxidase is a major source of superoxide anions in the pulmonary arteries (PA). We previously reported that intratracheal SOD improves oxygenation and restores endothelial nitric oxide (NO) synthase (eNOS) function in lambs with persistent pulmonary hypertension of the newborn (PPHN). In this study, we determined the effects of the NADPH oxidase inhibitor apocynin on oxygenation, reactive oxygen species (ROS) levels, and NO signaling in PPHN lambs. PPHN was induced in lambs by antenatal ligation of the ductus arteriosus 9 days prior to delivery. Lambs were treated with vehicle or apocynin (3 mg/kg intratracheally) at birth and then ventilated with 100% O(2) for 24 h. A significant improvement in oxygenation was observed in apocynin-treated lambs after 24 h of ventilation. Contractility of isolated fifth-generation PA to norepinephrine was attenuated in apocynin-treated lambs. PA constrictions to NO synthase (NOS) inhibition with N-nitro-l-arginine were blunted in PPHN lambs; apocynin restored contractility to N-nitro-l-arginine, suggesting increased NOS activity. Intratracheal apocynin also enhanced PA relaxations to the eNOS activator A-23187 and to the NO donor S-nitrosyl-N-acetyl-penicillamine. Apocynin decreased the interaction between NADPH oxidase subunits p22(phox) and p47(phox) and decreased the expression of Nox2 and p22(phox) in ventilated PPHN lungs. These findings were associated with decreased superoxide and 3-nitrotyrosine levels in the PA of apocynin-treated PPHN lambs. eNOS protein expression, endothelial NO levels, and tetrahydrobiopterin-to-dihydrobiopterin ratios were significantly increased in PA from apocynin-treated lambs, although cGMP levels did not significantly increase and phosphodiesterase-5 activity did not significantly decrease. NADPH oxidase inhibition with apocynin may improve oxygenation, in part, by attenuating ROS-mediated vasoconstriction and by increasing NOS activity.

GCH1, BH4 and pain

Understanding and consequently treating neuropathic pain effectively is a challenge for modern medicine, as unlike inflammation, which can be controlled relatively well, chronic pain due to nerve injury is refractory to most current therapeutics. Here we define a target pathway for a new class of analgesics, tetrahydrobiopterin (BH4) synthesis and metabolism. BH4 is an essential co-factor in the synthesis of serotonin, dopamine, epinephrine, norepinephrine and nitric oxide and as a result, its availability influences many systems, including neurons. Following peripheral nerve damage, levels of BH4 are dramatically increased in sensory neurons, consequently this has a profound effect on the physiology of these cells, causing increased activity and pain hypersensitivity. These changes are principally due to the upregulation of the rate limiting enzyme for BH4 synthesis GTP Cyclohydrolase 1 (GCH1). A GCH1 pain-protective haplotype which decreases pain levels in a variety of settings, by reducing the levels of endogenous activation of this enzyme, has been characterized in humans. Here we define the control of BH4 homeostasis and discuss the consequences of large perturbations within this system, both negatively via genetic mutations and after pathological increases in the production of this cofactor that result in chronic pain. We explain the nature of the GCH1 reduced-function haplotype and set out the potential for a ' BH4 blocking' drug as a novel analgesic.

Synthesis and recycling of tetrahydrobiopterin in endothelial function and vascular disease

Nitric oxide, generated by the nitric oxide synthase (NOS) enzymes, plays pivotal roles in cardiovascular homeostasis and in the pathogenesis of cardiovascular disease. The NOS cofactor, tetrahydrobiopterin (BH4), is an important regulator of NOS function, since BH4 is required to maintain enzymatic coupling of L-arginine oxidation, to produce NO. Loss or oxidation of BH4 to 7,8-dihydrobiopterin (BH2) is associated with NOS uncoupling, resulting in the production of superoxide rather than NO. In addition to key roles in folate metabolism, dihydrofolate reductase (DHFR) can 'recycle' BH2, and thus regenerate BH4. It is therefore likely that net BH4 cellular bioavailability reflects the balance between de novo BH4 synthesis, loss of BH4 by oxidation to BH2, and the regeneration of BH4 by DHFR. Recent studies have implicated BH4 recycling in the direct regulation of eNOS uncoupling, showing that inhibition of BH4 recycling using DHFR-specific siRNA and methotrexate treatment leads to eNOS uncoupling in endothelial cells and the hph-1 mouse model of BH4 deficiency, even in the absence of oxidative stress. These studies indicate that not only BH4 level, but the recycling pathways regulating BH4 bioavailability represent potential therapeutic targets and will be discussed in this review.

Maintenance of cellular tetrahydrobiopterin homeostasis

Tetrahydrobiopterin (BH4) is a multifunctional cofactor of aromatic amino acid hydroxylases and nitric oxide synthase (NOS) as well as an intracellular antioxidant in animals. Through regulation of NOS activity BH4 plays a pivotal role not only in a variety of normal cellular functions but also in the pathogenesis of cardiovascular and neurodegenerative diseases, which develop under oxidative stress conditions. It appears that a balanced interplay between BH4 and NOS is crucial for cellular fate. If cellular BH4 homeostasis maintained by BH4 synthesis and regeneration fails to cope with increased oxidative stress, NOS is uncoupled to generate superoxide rather than NO and, in turn, exacerbates impaired BH4 homeostasis, thereby leading to cell death. The fundamental biochemical events involved in the BH4-NOS interplay are essentially the same, as revealed in mammalian endothelial, cardiac, and neuronal cells. This review summarizes information on the cellular BH4 homeostasis in mammals, focusing on its regulation under normal and oxidative stress conditions.

An important role of increase in tetrahydrobiopterin via H2O2-JAK2 signalling pathway in late phase of ischaemic preconditioning

The goal of this study was to elucidate whether there is an increase in myocardial tetrahydrobiopterin (BH4), which is a cofactor for nitric oxide synthase, during the late phase of ischaemic preconditioning (IPC) leading to cardioprotection against myocardial infarction and, if so, to examine the induction mechanisms of BH4 synthesis. Rats were preconditioned with four cycles of 3 min left main coronary artery (LCA) occlusion followed by 10 min reperfusion. Twenty-four hours later, the rats were subjected to 20 min ischaemia by LCA ligation and 2 h reperfusion, and the infarct size was determined by 2,3,5-triphenyltetrazolium chloride staining. The IPC protocol reduced the infarct size, and increased the BH4 content and expression of GTP-cyclohydrolase I (GTPCH), which is the rate-limiting enzyme for BH4 synthesis. Administration of a GTPCH inhibitor attenuated both the reduction in infarct size and the increase in BH4 levels. Moreover, the increase in BH4 content was reduced by administration of catalase or a Janus tyrosine kinase-2 (JAK2) inhibitor. These observations suggest that upregulation of BH4 synthesis in the heart contributes to an acquisition of ischaemic tolerance in late IPC, and the increase in myocardial BH4 content seems to be mediated by the induction of GTPCH via the H(2)O(2)-JAK2 pathway.

Tetrahydrobiopterin, superoxide, and vascular dysfunction

(6R)-5,6,7,8-Tetrahydrobiopterin (BH(4)) is an endogenously produced pterin that is found widely distributed in mammalian tissues. BH(4) works as a cofactor of aromatic amino acid hydroxylases and nitric oxide synthases. In the vasculature a deficit of BH(4) is implicated in the mechanisms of several diseases including atherosclerosis, hypertension, diabetic vascular disease, and vascular complications from cigarette smoking and environmental pollution. These ill-effects are connected to the ability of BH(4) to regulate reactive oxygen species levels in the endothelium. The possibility of using BH(4) as a therapeutical agent in cardiovascular medicine is becoming more compelling and many biochemical and physiological aspects involved in this application are currently under investigation. This review summarizes our current understanding of BH(4) reactivity and some aspects of cellular production and regulation.

Nox5 and the regulation of cellular function

The NADPH oxidase (Nox) family of enzymes is comprised of seven members, Noxes 1-5 and the Duoxes 1 and 2. Nox5 was the last of the conventional Nox enzymes to be identified, and in comparison to its siblings, much less is known about its molecular regulation and even less regarding its functional significance. The loss of Nox5 from rodent genomes has contributed significantly to this deficit in knowledge, but recent discoveries have narrowed the gap. There are many differences between Nox5 and the other Nox isoforms including alternative splicing, transcriptional regulation, enzymatic control mechanisms, tissue distribution, and intracellular trafficking. The goal of this review is to outline recent advances in our knowledge of the genetic regulation, the molecular mechanisms governing its activity, and the functional significance of Nox5 in human physiology and pathophysiology.

GTP cyclohydrolase I expression, protein, and activity determine intracellular tetrahydrobiopterin levels, independent of GTP cyclohydrolase feedback regulatory protein expression

GTP cyclohydrolase I (GTPCH) is a key enzyme in the synthesis of tetrahydrobiopterin (BH4), a required cofactor for nitricoxide synthases and aromatic amino acid hydroxylases. Alterations of GTPCH activity and BH4 availability play an important role in human disease. GTPCH expression is regulated by inflammatory stimuli, in association with reduced expression of GTP cyclohydrolase feedback regulatory protein (GFRP). However, the relative importance of GTPCH expression versus GTPCH activity and the role of GFRP in relation to BH4 bioavailability remain uncertain. We investigated these relationships in a cell line with tet-regulated GTPCH expression and in the hph-1 mouse model of GTPCH deficiency. Doxycycline exposure resulted in a dose-dependent decrease in GTPCH protein and activity, with a strong correlation between GTPCH expression and BH4 levels (r(2) = 0.85, p < 0.0001). These changes in GTPCH and BH4 had no effect on GFRP expression or protein levels. GFRP overexpression and knockdown in tet-GCH cells did not alter GTPCH activity or BH4 levels, and GTPCH-specific knockdown in sEnd.1 endothelial cells had no effect on GFRP protein. In mouse liver we observed a graded reduction of GTPCH expression, protein, and activity, from wild type, heterozygote, to homozygote littermates, with a striking linear correlation between GTPCH expression and BH4 levels (r(2) = 0.82, p < 0.0001). Neither GFRP expression nor protein differed between wild type, heterozygote, nor homozygote mice, despite the substantial differences in BH4. We suggest that GTPCH expression is the primary regulator of BH4 levels, and changes in GTPCH or BH4 are not necessarily accompanied by changes in GFRP expression.

Superoxide dismutase restores eNOS expression and function in resistance pulmonary arteries from neonatal lambs with persistent pulmonary hypertension

Endothelial nitric oxide (NO) synthase (eNOS) expression and activity are decreased in fetal lambs with persistent pulmonary hypertension (PPHN). We sought to determine the impact of mechanical ventilation with O(2) with or without inhaled NO (iNO) or recombinant human SOD (rhSOD) on eNOS in the ductal ligation model of PPHN. PPHN lambs and age-matched controls were ventilated with 100% O(2) for 24 h alone or combined with 20 ppm iNO continuously or a single dose of rhSOD (5 mg/kg) given intratracheally at delivery. In 1-day spontaneously breathing lambs, eNOS expression in resistance pulmonary arteries increased relative to fetal levels. eNOS expression increased in control lambs ventilated with 100% O(2), but not in PPHN lambs. Addition of iNO or rhSOD increased eNOS expression and decreased generation of reactive oxygen species (ROS) in PPHN lambs relative to those ventilated with 100% O(2) alone. However, only rhSOD restored eNOS function, increased tetrahydrobiopterin (BH(4)), a critical cofactor for eNOS function, and restored GTP cyclohydrolase I expression in isolated vessels and lungs from PPHN lambs. These data suggest that ventilation of PPHN lambs with 100% O(2) increases ROS production, blunts postnatal increases in eNOS expression, and decreases available BH(4) in PPHN lambs. Although the addition of iNO or rhSOD diminished ROS production and increased eNOS expression, only rhSOD improved eNOS function and levels of available BH(4). Thus therapies designed to decrease oxidative stress and restore eNOS coupling, such as rhSOD, may prove useful in the treatment of PPHN in newborn infants.

A plaidoyer for cutaneous enzymology: our view of some important unanswered questions on the contributions of selected key enzymes to epidermal homeostasis

This review highlights the importance of enzymology, a field of great neglect in current cutaneous biology research. It was therefore the aim by using selected examples of epidermal enzymes and their action including some open questions to demonstrate the importance of this area. Clearly a thorough understanding of basic knowledge in this field is needed which in turn offers a plethora of innovative research projects for a curious mind. Moreover, in order to gain the closest understanding to the truth instead of generating esoteric results, emphasis is put forward on a holistic view utilizing a combination of modern and sometimes old methods to get the answer. Last but not least the bench work is only useful for the welfare of our patients if we can apply our basic knowledge.

Oral administration of tetrahydrobiopterin attenuates testicular damage by reducing nitric oxide synthase activity in a cryptorchid mouse model

Experimental cryptorchidism has been shown to induce germ cell apoptosis. Nitric oxide (NO), a ubiquitous free radical produced by NO synthases (NOSs), has been associated with apoptosis in a number of cell types. However, the regulation of NOSs in experimental cryptorchid testes remains unknown. Tetrahydrobiopterin (BH4), an essential cofactor of NOS, plays an important role in the generation of NO. It has been reported that activation of the immune system stimulates an increase in endogenous BH4 rate-limiting enzyme GTP cyclohydrolase I (GTPCH I) activity, resulting in an increase in intracellular BH4 levels and BH4-dependent NO synthesis in various cells. We examined the effect of dietary treatment with BH4 on GTPCH I, BH4 synthesis, NO production, and testicular damage in cryptorchid model mice. Male mice were treated with oral BH4 starting from age 4 weeks or received standard diet only, and right cryptorchid testes were created surgically at age 10 weeks. The testes were evaluated 0, 3, 5, 7, and 10 days after surgery by assays of testicular weight, BH4 and dihydrobiopterin (oxidized BH4) levels, GTPCH I mRNA levels, NOS protein expression levels, NO concentration, and nitrotyrosine (product of ONOO(-); determinant of NO-dependent damage) levels. In untreated mice, GTPCH I mRNA and BH4 levels increased and eNOS protein expression, NO concentration, and nitrotyrosine levels increased gradually. BH4 treatment decreased GTPCH I mRNA and BH4 levels, with concomitant reduction of eNOS protein levels, nitrotyrosine levels, and NO concentration, resulting in reduced testicular damage. Our findings demonstrate that supplementation with BH4 could provide a new therapeutic intervention for heat stress-based testicular dysfunction.

4-Hydroxy-2-nonenal increases superoxide anion radical in endothelial cells via stimulated GTP cyclohydrolase proteasomal degradation

OBJECTIVE

4-Hydroxy-2-nonenal (4-HNE) is an abundant electrophilic lipid that mediates oxidative stress in endothelium by mechanisms that remain controversial. This study examines the effects of 4-HNE on nitric oxide (NO) and superoxide levels in bovine aorta endothelial cells (BAECs).

METHODS AND RESULTS

Exposure of BAECs to 4-HNE caused a dose-dependent inhibition of NO that correlated with losses of hsp90 and phosphorylated eNOS-serine1179 but not eNOS protein levels. 4-HNE failed to inhibit NO production in sepiapterin and ascorbate supplemented cells suggesting that tetrahydrobiopterin (BH4) is a limiting factor in non supplemented cells. This was verified by quantification of BH4 by high-performance liquid chromatography analysis with electrochemical detection and by examining GTP cyclohydrolase I (GTPCH) protein levels and activity all of which were diminished by 4-HNE treatment. Analysis of 2-hydroxyethidium indicated that 4-HNE increased superoxide release in BAECs. The effects of 4-HNE on GTPCH and hsp90 were efficiently counteracted by proteasomal inhibition, indicating that depletion of BH4 by 4-HNE is attributable to specific mechanisms involving protein degradation.

CONCLUSIONS

4-HNE by altering BH4 homeostasis mediates eNOS-uncoupling and superoxide generation in BAECs. By also decreasing phosphorylation of eNOS-serine 1179 4-HNE may specifically regulate NO/reactive oxygen species fluxes in the endothelium with important consequences to redox signaling.

Hydrogen peroxide stimulates tetrahydrobiopterin synthesis through activation of the Jak2 tyrosine kinase pathway in vascular endothelial cells

Tetrahydrobiopterin (BH4) is an essential cofactor for nitric oxide synthase (NOS). We previously described that hydrogen peroxide (H(2)O(2)) increases BH4 levels through the induction of GTP-cyclohydrolase I (GTPCH), which is the rate-limiting enzyme for the synthesis of BH4, in vascular endothelial cells. The aim of this study was to examine the underlying mechanism of H(2)O(2)-induced BH4 synthesis in vascular endothelial cells. The increases in BH4 levels induced by H(2)O(2) were strongly reduced by a Janus kinase-2 (Jak2) inhibitor, AG490. The H(2)O(2)-induced increases in GTPCH mRNA expression and GTPCH activity were also blocked by treatment with AG490. H(2)O(2) elicited an increase in the level of phosphorylated Jak2, suggesting that the induction of BH4 by H(2)O(2) was mediated by the Jak2 pathway. Signal transducers and activators of transcription (Stats) are the best-known substrates for Jak2. The H(2)O(2)-induecd increases in BH4 levels were reduced by treatment with fludarabine, which is shown to cause a specific depletion of Stat1 protein but not of other Stats. Moreover, H(2)O(2) caused the DNA binding of Stat1, and this was inhibited by AG490. Stat1 phosphorylation was enhanced by H(2)O(2) treatment, and the phosphorylation was attenuated by AG490. These findings suggest that the stimulation of BH4 synthesis through the induction of GTPCH is mediated at least in-part by the Jak2-Stat1 pathway.

Regulation of tetrahydrobiopterin biosynthesis by shear stress

An essential cofactor for the endothelial NO synthase is tetrahydrobiopterin (H4B). In the present study, we show that in human endothelial cells, laminar shear stress dramatically increases H4B levels and enzymatic activity of GTP cyclohydrolase (GTPCH)-1, the first step of H4B biosynthesis. In contrast, protein levels of GTPCH-1 were not affected by shear. Shear did not change protein expression or activity of the downstream enzymes 6-pyruvoyl-tetrahydropterin synthase and sepiapterin reductase and decreased protein levels of the salvage enzyme dihydrofolate reductase. Oscillatory shear only modestly affected H4B levels and GPTCH-1 activity. We also demonstrate that laminar, but not oscillatory shear stress, stimulates phosphorylation of GTPCH-1 on serine 81 and that this is mediated by the alpha prime (alpha') subunit of casein kinase 2. The increase in H4B caused by shear is essential in allowing proper function of endothelial NO synthase because GPTCH-1 blockade with 2,4-diamino-6-hydroxypyrimidine during shear inhibited dimer formation of endothelial NO synthase, increased endothelial cell superoxide production, and prevented the increase in NO production caused by shear. Thus, shear stress not only increases endothelial NO synthase levels but also stimulates production of H4B by markedly enhancing GTPCH-1 activity via casein kinase 2-dependent phosphorylation on serine 81. These findings illustrate a new function of casein kinase 2 in the endothelium and provide insight into regulation of GTPCH-1 activity.

Alterations in gene expression in rat skin exposed to 56Fe ions and dietary vitamin A acetate

The purpose of the present work was to examine gene expression patterns in rat skin exposed to a beam of (56)Fe ions, a surrogate for the high-energy, heavy-ion galactic radiation background, as a basis for obtaining a better understanding of the possible mechanism(s) behind the radioprotective activity of vitamin A. A 2 x 4-cm rectangle of dorsal rat skin was exposed to 1.01 GeV/nucleon (56)Fe ions generated by the Alternating Gradient Synchrotron at Brookhaven National Laboratory. Gene expression patterns were monitored in either the presence or absence of a 250-ppm dietary supplement of vitamin A acetate in powdered lab chow. Although vitamin A and other retinoids show anti-carcinogenic activity in several animal models, the underlying changes in gene expression have not been examined extensively. At either 1 or 7 day after irradiation, a 1-cm square of irradiated and control rat skin was excised and analyzed using the Affymetrix rat microarray (RG_U34A) system. Microarray responses were displayed and processed by GeneSpring 7.0 and GOTree software. At 1 day after 3 Gy of (56)Fe-ion irradiation, the expression of 110 genes was significantly up-regulated (P < = 0.05) in comparison to levels in control rat skin, while no genes were altered by the vitamin A acetate supplement alone. Combined with (56)Fe-ion radiation, the vitamin A acetate supplement blocked the expression of 88 (80%) of the 110 genes and eliminated 16 of 18 gene categories that were significantly altered (all increased) by the (56)Fe-ion radiation. Categories with large numbers of genes eliminated by the retinoid included response to stress, 33 genes; response to biotic stimulus, 38 genes; signal transduction, 35 genes; and regulation of cellular/physiological process, 40 genes. Even for immune response and response to biotic stimulus, the only two categories that remained significantly altered in the presence of the vitamin, the combined number of altered genes was reduced from 74 to 13. No significant alterations in gene expression were found at 7 days relative to the numbers in controls. The results indicate that at 1 day dietary vitamin A acetate strongly interfered with (56)Fe-ion-induced gene expression within the broad categories of stimulus- and stress-related genes, implying that the latter gene categories likely play a role in the radioprotective action of the vitamin.

Mechanisms of H2O2-induced oxidative stress in endothelial cells

Hydrogen peroxide, produced by inflammatory and vascular cells, induces oxidative stress that may contribute to endothelial dysfunction. In smooth muscle cells, H(2)O(2) induces production of O(2)*(-) by activating NADPH oxidase. However, the mechanisms whereby H(2)O(2) induces oxidative stress in endothelial cells are poorly understood. We examined the effects of H(2)O(2) on O(2)*(-) levels on porcine aortic endothelial cells (PAEC). Treatment with 60 micromol/L H(2)O(2) markedly increased intracellular O(2)*(-) levels (determined by conversion of dihydroethidium to hydroxyethidium) and produced cytotoxicity (determined by propidium iodide staining) in PAEC. Overexpression of human manganese superoxide dismutase in PAEC reduced O(2)*(-) levels and attenuated cytotoxicity resulting from treatment with H(2)O(2). L-NAME, an inhibitor of nitric oxide synthase (NOS), and apocynin, an inhibitor of NADPH oxidase, reduced O(2)*(-) levels in PAEC treated with H(2)O(2), suggesting that both NOS and NADPH oxidase contribute to H(2)O(2)-induced O(2)*(-) in PAEC. Inhibition of NADPH oxidase using apocynin and NOS rescue with L-sepiapterin together reduced O(2)*(-) levels in PAEC treated with H(2)O(2) to control levels. This suggests interaction-distinct NOS and NADPH oxidase pathways to superoxide. We conclude that H(2)O(2) produces oxidative stress in endothelial cells by increasing intracellular O(2)*(-) levels through NOS and NADPH oxidase. These findings suggest a complex interaction between H(2)O(2) and oxidant-generating enzymes that may contribute to endothelial dysfunction.

Reduction of myocardial infarct size by tetrahydrobiopterin: possible involvement of mitochondrial KATP channels activation through nitric oxide production

This study examined whether intravenous administration of tetrahydrobiopterin (BH4) reduces myocardial infarct size following ischemia/reperfusion (I/R) in rats, and the mechanisms of its protective effect were also investigated. Rats were subjected to 30 minutes of ischemia by ligation of the left coronary artery and 2 hours of reperfusion. The infarct size was determined as a percentage of the area at risk by triphenyltetrazolium staining. Intravenous administration of BH4 (0.01 mg/kg-1 mg/kg) significantly reduced the myocardial infarct size. Nitrite plus nitrate (NOx) and cGMP levels in the hearts were significantly increased by the treatment with BH4, and the infarct size-limiting effect of BH4 was abolished by the co-administration of NG-nitro-L-arginine methyl ester, a specific inhibitor of nitric oxide synthase, or 5-hydroxydecanoic acid, a specific inhibitor of mitochondrial ATP-sensitive potassium channel (mitoKATP channel). These findings suggest that BH4 has a cardioprotective effect against I/R in vivo, and its protective effect appeared to be involved in the opening of mitoKATP channels through increased nitric oxide production.

Whole-genome transcriptional analysis of heavy metal stresses in Caulobacter crescentus

The bacterium Caulobacter crescentus and related stalk bacterial species are known for their distinctive ability to live in low-nutrient environments, a characteristic of most heavy metal-contaminated sites. Caulobacter crescentus is a model organism for studying cell cycle regulation with well-developed genetics. We have identified the pathways responding to heavy-metal toxicity in C. crescentus to provide insights for the possible application of Caulobacter to environmental restoration. We exposed C. crescentus cells to four heavy metals (chromium, cadmium, selenium, and uranium) and analyzed genome-wide transcriptional activities postexposure using an Affymetrix GeneChip microarray. C. crescentus showed surprisingly high tolerance to uranium, a possible mechanism for which may be the formation of extracellular calcium-uranium-phosphate precipitates. The principal response to these metals was protection against oxidative stress (up-regulation of manganese-dependent superoxide dismutase sodA). Glutathione S-transferase, thioredoxin, glutaredoxins, and DNA repair enzymes responded most strongly to cadmium and chromate. The cadmium and chromium stress response also focused on reducing the intracellular metal concentration, with multiple efflux pumps employed to remove cadmium, while a sulfate transporter was down-regulated to reduce nonspecific uptake of chromium. Membrane proteins were also up-regulated in response to most of the metals tested. A two-component signal transduction system involved in the uranium response was identified. Several differentially regulated transcripts from regions previously not known to encode proteins were identified, demonstrating the advantage of evaluating the transcriptome by using whole-genome microarrays.

Oxidative stress and nitric oxide deficiency in the kidney: a critical link to hypertension?

There is growing evidence that oxidative stress contributes to hypertension. Oxidative stress can precede the development of hypertension. In almost all models of hypertension, there is oxidative stress that, if corrected, lowers BP, whereas creation of oxidative stress in normal animals can cause hypertension. There is overexpression of the p22(phox) and Nox-1 components of NADPH oxidase and reduced expression of extracellular superoxide dismutase (EC-SOD) in the kidneys of ANG II-infused rodents, whereas there is overexpression of p47(phox) and gp91(phox) and reduced expression of intracellular SOD with salt loading. Several mechanisms have been identified that can make oxidative stress self-sustaining. Reactive oxygen species (ROS) can enhance afferent arteriolar tone and reactivity both indirectly via potentiation of tubuloglomerular feedback and directly by microvascular mechanisms that diminish endothelium-derived relaxation factor/nitric oxide responses, generate a cyclooxygenase-2-dependent endothelial-derived contracting factor that activates thromboxane-prostanoid receptors, and enhance vascular smooth muscle cells reactivity. ROS can diminish the efficiency with which the kidney uses O(2) for Na(+) transport and thereby diminish the P(O(2)) within the kidney cortex. This may place a break on further ROS generation yet could further enhance vasculopathy and hypertension. There is a tight relationship between oxidative stress in the kidney and the development and maintenance of hypertension.

Inhaled nitric oxide induced NOS inhibition and rebound pulmonary hypertension: a role for superoxide and peroxynitrite in the intact lamb

Previous in vivo studies indicate that inhaled nitric oxide (NO) decreases nitric oxide synthase (NOS) activity and that this decrease is associated with significant increases in pulmonary vascular resistance (PVR) upon the acute withdrawal of inhaled NO (rebound pulmonary hypertension). In vitro studies suggest that superoxide and peroxynitrite production during inhaled NO therapy may mediate these effects, but in vivo data are lacking. The objective of this study was to determine the role of superoxide in the decrease in NOS activity and rebound pulmonary hypertension associated with inhaled NO therapy in vivo. In control lambs, 24 h of inhaled NO (40 ppm) decreased NOS activity by 40% (P<0.05) and increased endothelin-1 levels by 64% (P<0.05). Withdrawal of NO resulted in an acute increase in PVR (60.7%, P<0.05). Associated with these changes, superoxide and peroxynitrite levels increased more than twofold (P<0.05) following 24 h of inhaled NO therapy. However, in lambs treated with polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) during inhaled NO therapy, there was no change in NOS activity, no increase in superoxide or peroxynitrite levels, and no increase in PVR upon the withdrawal of inhaled NO. In addition, endothelial NOS nitration was 18-fold higher (P<0.05) in control lambs than in PEG-SOD-treated lambs following 24 h of inhaled NO. These data suggest that superoxide and peroxynitrite participate in the decrease in NOS activity and rebound pulmonary hypertension associated with inhaled NO therapy. Reactive oxygen species scavenging may be a useful therapeutic strategy to ameliorate alterations in endogenous NO signaling during inhaled NO therapy.

Endothelial dihydrofolate reductase: critical for nitric oxide bioavailability and role in angiotensin II uncoupling of endothelial nitric oxide synthase

Recent studies demonstrate that oxidative inactivation of tetrahydrobiopterin (H4B) may cause uncoupling of endothelial nitric oxide synthase (eNOS) to produce superoxide (O2*-). H4B was found recyclable from its oxidized form by dihydrofolate reductase (DHFR) in several cell types. Functionality of the endothelial DHFR, however, remains completely unknown. Here we present findings that specific inhibition of endothelial DHFR by RNA interference markedly reduced endothelial H4B and nitric oxide (NO.) bioavailability. Furthermore, angiotensin II (100 nmol/liter for 24 h) caused a H4B deficiency that was mediated by H2O2-dependent down-regulation of DHFR. This response was associated with a significant increase in endothelial O2*- production, which was abolished by eNOS inhibitor N-nitro-L-arginine-methyl ester or H2O2 scavenger polyethylene glycol-conjugated catalase, strongly suggesting H2O2-dependent eNOS uncoupling. Rapid and transient activation of endothelial NAD(P)H oxidases was responsible for the initial burst production of O2* (Rac1 inhibitor NSC 23766 but not an N-nitro-L-arginine-methyl ester-attenuated ESR O2*- signal at 30 min) in response to angiotensin II, preceding a second peak in O2*- production at 24 h that predominantly depended on uncoupled eNOS. Overexpression of DHFR restored NO. production and diminished eNOS production of O2*- in angiotensin II-stimulated cells. In conclusion, these data represent evidence that DHFR is critical for H4B and NO. bioavailability in the endothelium. Endothelial NAD(P)H oxidase-derived H2O2 down-regulates DHFR expression in response to angiotensin II, resulting in H4B deficiency and uncoupling of eNOS. This signaling cascade may represent a universal mechanism underlying eNOS dysfunction under pathophysiological conditions associated with oxidant stress.

Tetrahydrobiopterin and nitric oxide synthase dimer levels are not changed following hypoxia-ischemia in the newborn rat

The effect of hypoxia-ischemia on the nitric oxide synthase (NOS) cofactor tetrahydrobiopterin (BH4) and changes in the enzyme dimer state have not previously been studied. Cell-based studies have demonstrated the regulation of nitric oxide (NO) synthesis by intracellular BH4 levels. Activation of NOS requires two NOS polypeptides to form a homodimer. Dimerization results in the creation of high-affinity binding sites for BH4 and L-arginine. Our previous studies have indicated that nNOS activity falls 2 h post-hypoxia-ischemia in the immature rodent model. Thus, the objective of this study was to determine whether changes in nNOS dimeric state could be responsible for the decrease in nNOS activity. Using the immature rat model of HI in conjunction with LT-PAGE and Western blot analysis, we determined the effect of HI on NOS dimer state in hippocampus and cortex and the effects of pharmacologic modulation of NO levels during HI on dimer formation. Using high-performance liquid chromatography (HPLC) and electrospray tandem mass spectrometry (MS-MS), we measured BH4 and L-arginine levels respectively after HI under the same conditions. We found minimal or no changes in either BH4 levels or NOS dimer state at 2 h, 24 h and 7 day recovery from HI on postnatal day 7. In contrast, L-arginine levels were transiently increased in the hypoxic ischemic hemisphere. Thus, our data suggest that the previously described decrease in NOS activity after HI is not associated with depletion of the cofactor BH4, L-arginine substrate or changes in the NOS enzyme dimer state.

Possible involvement of hydroxyl radical on the stimulation of tetrahydrobiopterin synthesis by hydrogen peroxide and peroxynitrite in vascular endothelial cells

We recently described that hydrogen peroxide (H2O2) stimulates the synthesis of tetrahydrobiopterin (BH4) through the induction of the rate-limiting enzyme GTP-cyclohydrolase I (GTPCH), and increases tetrahydrobiopterin content in vascular endothelial cells. Tetrahydrobiopterin is easily oxidized by peroxynitrite (ONOO-), but not by hydrogen peroxide. The aim of this study was to determine the effect of hydroxyl radical and peroxynitrite, which are both toxic biological oxidants, on tetrahydrobiopterin synthesis and the regulation of its content in vascular endothelial cells. In the cell-free assay system, tetrahydrobiopterin was rapidly oxidized by the hydroxyl radical and peroxynitrite, but not by hydrogen peroxide. However, the addition of not only hydrogen peroxide but also the hydroxyl radical and peroxynitrite to vascular endothelial cells transiently decreased tetrahydrobiopterin content, and then markedly increased its content. Interestingly, total biopterin content was also decreased by early treatment with oxidants. Moreover, oxidants induced the expression of GTP-cyclohydrolase I, and the increase of the tetrahydrobiopterin content was blocked by the treatment with GTP-cyclohydrolase I inhibitor. Both the hydrogen peroxide- and peroxynitrite-induced increases in tetrahydrobiopterin content and findings suggest that not only hydrogen peroxide but also the hydroxyl radical and peroxynitrite stimulates tetrahydrobiopterin synthesis through GTP-cyclohydrolase I expression, and that the hydroxyl radical plays a central role in the stimulation of tetrahydrobiopterin synthesis. Moreover, the transient decrease in BH4 to tetrahydrobiopterin.

Changes in tetrahydrobiopterin levels in endothelial cells and adult cardiomyocytes induced by LPS and hydrogen peroxide--a role for GFRP?

Alterations in tetrahydrobiopterin (BH4) levels have significant consequences in vascular pathophysiology. However, the mechanisms regulating BH4 remain poorly understood. The activity of GTP cyclohydrolase I (GTPCH-I), the first enzyme in BH4 biosynthesis, is controlled by protein levels, posttranslational modifications and interaction with GTPCH-I feedback regulatory protein (GFRP). This work examined the correlation between GTPCH-I protein levels and activity and changes in BH4 in human endothelial cells (HAECs) and adult rat cardiomyocytes (ARCM). Changes in BH4 were stimulated with LPS in HAECs and ARCM, and with hydrogen peroxide in HAECs only. Biopterin production by HAECs and ARCM were attained with concentrations of LPS >>1 microg/ml and responses were nonlinear with respect to LPS concentrations. Western blot analysis demonstrated that induction of biopterin synthesis in HAECs and ARCM by LPS does not entail augmentation of constitutive GTPCH-I protein levels. However, LPS diminished GFRP mRNA, suggesting that disruption of GTPCH-I:GFRP complex enhances de novo biopterin synthesis. Conversely, treatment with hydrogen peroxide increased GTPCH-I and GFRP mRNA levels in HAECs while depleting BH4 and GSH, which was counteracted by catalase. This indicates that GFRP may override increases in GTPCH-I protein inhibiting enzyme activity. This conclusion is further supported by depletion of biopterin in cells transiently transfected with GFRP. Thus, allosteric regulation of GTPCH-I activity in the cardiovascular system maybe an important mechanism regulating BH4 levels through GFRP signaling.

Reduction of GTP cyclohydrolase I feedback regulating protein expression by hydrogen peroxide in vascular endothelial cells

We examined the effect of H(2)O(2) on the expression of GTP cyclohydrolase I (GTPCH) feedback regulating protein (GFRP). Addition of H(2)O(2) to endothelial cells decreased GFRP mRNA levels, in contrast to the increase of tetrahydrobiopterin (BH(4)) content and GTPCH mRNA levels. The inhibitors of nitric oxide (NO) synthase and GTPCH had no influence on the decrease of GFRP mRNA levels in H(2)O(2)-treated cells. It is suggested that H(2)O(2) induces BH(4) synthesis through not only induction of GTPCH but also reduction of GFRP. The decrease of GFRP mRNA level appears to be independent of the produced NO and BH(4).

Hemodynamic and biochemical adaptations to vascular smooth muscle overexpression of p22phox in mice

Protein levels and polymorphisms of p22 phox have been suggested to modulate vascular NAD(P)H oxidase activity and vascular production of reactive oxygen species (ROS). We sought to determine whether increasing p22 phox expression would alter vascular ROS production and hemodynamics by targeting p22 phox expression to smooth muscle in transgenic (Tg) mice. Aortas of Tg p22smc mice had increased p22 phox and Nox1 protein levels and produced more superoxide and H2O2. Surprisingly, endothelium-dependent relaxation and blood pressure in Tg p22smc mice were normal. Aortas of Tg p22smc mice produced twofold more nitric oxide (NO) at baseline and sevenfold more NO in response to calcium ionophore as detected by electron spin resonance. Western blot analysis revealed a twofold increase in endothelial NO synthase (eNOS) protein expression in Tg p22smc mice. Both eNOS expression and NO production were normalized by infusion of the glutathione peroxidase mimetic ebselen or by crossing Tg p22smc mice with mice overexpressing catalase. We have previously found that NO stimulates extracellular superoxide dismutase (ecSOD) expression in vascular smooth muscle. In keeping with this, aortic segments from Tg p22smc mice expressed twofold more ecSOD, and chronic treatment with the NOS inhibitor NG-nitro-l-arginine methyl ester normalized this, suggesting that NO regulates ecSOD protein expression in vivo. These data indicate that chronic oxidative stress caused by excessive H2O2 production evokes a compensatory response involving increased eNOS expression and NO production. NO in turn increases ecSOD protein expression and counterbalances increased ROS production leading to the maintenance of normal vascular function and hemodynamics.

Gene Therapy of Endothelial Nitric Oxide Synthase and Manganese Superoxide Dismutase Restores Delayed Wound Healing in Type 1 Diabetic Mice

Background— Nitric oxide (NO) deficiency contributes to diabetic wound healing impairment. The present study tested the hypothesis that increased cutaneous superoxide (O 2 − ) levels in type 1 diabetic mice cause NO deficiency and delayed wound healing.

Methods and Results— Wound healing was markedly delayed in streptozotocin-induced type 1 diabetic mice compared with the normal controls. There were significantly reduced levels of endothelial NO synthase (eNOS) protein and constitutive NOS activity in diabetic wounds, whereas O 2 − levels were markedly increased. A single regimen of cutaneous gene therapy of eNOS or manganese superoxide dismutase (MnSOD) restored such healing delay, with a concomitant suppression of wound O 2 − levels and augmentation of both eNOS protein and constitutive NOS activity. Gene therapy of MnSOD also increased cutaneous MnSOD activity. Cutaneous O 2 − levels were also increased in Ins2 Akita diabetic mice. In vitro glucose treatment of cutaneous tissues from normal mice for 24 hours increased O 2 − levels in a concentration-dependent manner. The enhanced cutaneous O 2 − levels induced by high glucose in both normal and diabetic mice were abolished by the NADPH oxidase inhibitor apocynin and the protein kinase C inhibitor chelerythrine. Furthermore, ex vivo gene transfer of dominant-negative HA-tagged N17Rac1, which inhibits NADPH oxidase subunit Rac1, significantly inhibited cutaneous O 2 − formation induced by high glucose in both normal and Ins2 Akita diabetic mice.

Conclusions— These results indicate that hyperglycemia augments cutaneous O 2 − levels, at least in part, via NADPH oxidase and protein kinase C pathways, resulting in impaired wound healing in type 1 diabetic mice. Gene therapy strategies aimed at restoring cutaneous NO bioavailability may provide an effective means to ameliorate delayed diabetic wound healing.

Human phenylalanine hydroxylase is activated by H2O2: a novel mechanism for increasing the l-tyrosine supply for melanogenesis in melanocytes

Epidermal phenylalanine hydroxylase (PAH) produces L-tyrosine from the essential amino acid L-phenylalanine supporting melanogenesis in human melanocytes. Those PAH activities increase linearly in the different skin phototypes I-VI (Fitzpatrick classification) and also increase up to 24h after UVB light with only one minimal erythemal dose. Since UVB generates also H(2)O(2), we here asked the question whether this reactive oxygen species could influence the activity of pure recombinant human PAH. Under saturating conditions with the substrate L-phenylalanine (1x10(-3)M), the V(max) for enzyme activity increased 4-fold by H(2)O(2) (>2.0x10(-3)M). Lineweaver-Burk analysis identified a mixed activation mechanism involving both the regulatory and catalytic domains of PAH. Hyperchem molecular modelling and Deep View analysis support oxidation of the single Trp(120) residue to 5-OH-Trp(120) by H(2)O(2) causing a conformational change in the regulatory domain. PAH was still activated by H(2)O(2) in the presence of the electron donor/cofactor 6(R)-L-erythro-5,6,7,8-tetrahydrobiopterin despite slow oxidation of this cofactor. In vivo FT-Raman spectroscopy confirmed decreased epidermal phenylalanine in association with increased tyrosine after UVB exposure. Hence, generation of H(2)O(2) by UVB can activate epidermal PAH leading to an increased L-tyrosine pool for melanogenesis.