Tetrahydrobiopterin, superoxide, and vascular dysfunction

Replicative Endothelial Cell Senescence May Lead to Endothelial Dysfunction by Increasing the BH2/BH4 Ratio Induced by Oxidative Stress, Reducing BH4 Availability, and Decreasing the Expression of eNOS

Vascular aging is associated with the development of cardiovascular complications, in which endothelial cell senescence (ES) may play a critical role. Nitric oxide (NO) prevents human ES through inhibition of oxidative stress, and inflammatory signaling by mechanisms yet to be elucidated. Endothelial cells undergo an irreversible growth arrest and alter their functional state after a finite number of divisions, a phenomenon called replicative senescence. We assessed the contribution of NO during replicative senescence of human aortic (HAEC) and coronary (CAEC) endothelial cells, in which accumulation of the senescence marker SA-β-Gal was quantified by β-galactosidase staining on cultured cells. We found a negative correlation in passaged cell cultures from P0 to P12, between a reduction in NO production with increased ES and the formation of reactive oxygen (ROS) and nitrogen (ONOO-) species, indicative of oxidative and nitrosative stress. The effect of ES was evidenced by reduced expression of endothelial Nitric Oxide Synthase (eNOS), Interleukin Linked Kinase (ILK), and Heat shock protein 90 (Hsp90), alongside a significant increase in the BH2/BH4 ratio, inducing the uncoupling of eNOS, favoring the production of superoxide and peroxynitrite species, and fostering an inflammatory environment, as confirmed by the levels of Cyclophilin A (CypA) and its receptor Extracellular Matrix Metalloprotease Inducer (EMMPRIN). NO prevents ES by preventing the uncoupling of eNOS, in which oxidation of BH4, which plays a key role in eNOS producing NO, may play a critical role in launching the release of free radical species, triggering an aging-related inflammatory response.

BH4 as a Therapeutic Target for ADHD: Relevance to Neurotransmitters and Stress-Driven Symptoms

Tetrahydrobiopterin (BH4) is a critical cofactor in a variety of metabolic pathways that have been linked to ADHD. There have been no previous studies utilizing BH4 as a supplement for ADHD. BH4 has been approved as a treatment for phenylketonuria (PKU). Individuals with PKU and ADHD appear to have low DA levels in common, suggesting that the hypodopaminergic state seen in both illnesses could be a relationship between the two. Clinical research involving supplementation of BH4 has shown low occurrence of adverse. In experiments, BH4 has also been found to have good blood-brain barrier permeability. BH4 also has the ability in scavenging ROS activity, which is an implication of stress and is seen in ADHD. BH4's significance in ADHD is reviewed in this paper because of its involvement in numerous neurodevelopmental metabolic pathways, and we anticipate that exogenous BH4 can be used to treat ADHD.

Insights into Molecular Structure of Pterins Suitable for Biomedical Applications

Pterins are an inseparable part of living organisms. Pterins participate in metabolic reactions mostly as tetrahydropterins. Dihydropterins are usually intermediates of these reactions, whereas oxidized pterins can be biomarkers of diseases. In this review, we analyze the available data on the quantum chemistry of unconjugated pterins as well as their photonics. This gives a comprehensive overview about the electronic structure of pterins and offers some benefits for biomedicine applications: (1) one can affect the enzymatic reactions of aromatic amino acid hydroxylases, NO synthases, and alkylglycerol monooxygenase through UV irradiation of H₄pterins since UV provokes electron donor reactions of H₄pterins; (2) the emission properties of H₂pterins and oxidized pterins can be used in fluorescence diagnostics; (3) two-photon absorption (TPA) should be used in such pterin-related infrared therapy because single-photon absorption in the UV range is inefficient and scatters in vivo; (4) one can affect pathogen organisms through TPA excitation of H₄pterin cofactors, such as the molybdenum cofactor, leading to its detachment from proteins and subsequent oxidation; (5) metal nanostructures can be used for the UV-vis, fluorescence, and Raman spectroscopy detection of pterin biomarkers. Therefore, we investigated both the biochemistry and physical chemistry of pterins and suggested some potential prospects for pterin-related biomedicine.

Cellular Stress-Induced Metabolites in Escherichia coli

Escherichia coli isolates commonly inhabit the human microbiota, yet the majority of E. coli's small-molecule repertoire remains uncharacterized. We previously employed erythromycin-induced translational stress to facilitate the characterization of autoinducer-3 (AI-3) and structurally related pyrazinones derived from "abortive" tRNA synthetase reactions in pathogenic, commensal, and probiotic E. coli isolates. In this study, we explored the "missing" tryptophan-derived pyrazinone reaction and characterized two other families of metabolites that were similarly upregulated under erythromycin stress. Strikingly, the abortive tryptophanyl-tRNA synthetase reaction leads to a tetracyclic indole alkaloid metabolite (1) rather than a pyrazinone. Furthermore, erythromycin induced two naphthoquinone-functionalized metabolites (MK-hCys, 2; and MK-Cys, 3) and four lumazines (7-10). Using genetic and metabolite analyses coupled with biomimetic synthesis, we provide support that the naphthoquinones are derived from 4-dihydroxy-2-naphthoic acid (DHNA), an intermediate in the menaquinone biosynthetic pathway, and the amino acids homocysteine and cysteine. In contrast, the lumazines are dependent on a flavin intermediate and α-ketoacids from the aminotransferases AspC and TyrB. We show that one of the lumazine members (9), an indole-functionalized analogue, possesses antioxidant properties, modulates the anti-inflammatory fate of isolated TH17 cells, and serves as an aryl-hydrocarbon receptor (AhR) agonist. These three systems described here serve to illustrate that new metabolic branches could be more commonly derived from well-established primary metabolic pathways.

The Role of Reactive Species on Innate Immunity

This review examines the role of reactive species RS (of oxygen ROS, nitrogen RNS and halogen RHS) on innate immunity. The importance of these species in innate immunity was first recognized in phagocytes that underwent a “respiratory burst” after activation. The anion superoxide ^•O₂⁻ and hydrogen peroxide H₂O₂ are detrimental to the microbial population. NADPH oxidase NOx, as an ^•O₂⁻ producer is essential for microbial destruction, and patients lacking this functional oxidase are more susceptible to microbial infections. Reactive nitrogen species RNS (the most important are nitric oxide radical -^•NO, peroxynitrite ONOO^— and its derivatives), are also harmful to microorganisms, including bacteria, viruses, and parasites. Hypochlorous acid HOCl and hypothiocyanous acid HOSCN synthesized through the enzyme myeloperoxidase MPO, which catalyzes the reaction between H₂O₂ and Cl⁻ or SCN⁻, are important inorganic bactericidal molecules, effective against a wide range of microbes. This review also discusses the role of antimicrobial peptides AMPs and their induction of ROS. In summary, reactive species RS are the heart of the innate immune system, and they are necessary for microbial lysis in infections that can affect mammals throughout their lives.

Tetrahydrobiopterin in Cell Function and Death Mechanisms

Significance: Tetrahydrobiopterin (BH4) is most well known as a required cofactor for enzymes regulating cellular redox homeostasis, aromatic amino acid metabolism, and neurotransmitter synthesis. Less well known are the effects dependent on the cofactor's availability, factors governing its synthesis and recycling, redox implications of the cofactor itself, and protein-protein interactions that underlie cell death. This review provides an understanding of the recent advances implicating BH4 in the mechanisms of cell death and suggestions of possible therapeutic interventions. Recent Advances: The levels of BH4 often reflect the sum of synthetic and recycling enzyme activities. Enhanced expression of GTP cyclohydrolase, the rate-limiting enzyme in biosynthesis, increases BH4, leading to improved cell function and survival. Pharmacologically increasing BH4 levels has similar beneficial effects, leading to enhanced production of neurotransmitters and nitric oxide or reducing oxidant levels. The GTP cyclohydrolase-BH4 pairing has been implicated in a type of cell death, ferroptosis. At the cellular level, BH4 counteracts anticancer therapies directed to enhance ferroptosis via glutathione peroxidase 4 (GPX4) activity inhibition. Critical Issues: Because of the multitude of intertwined mechanisms, a clear relationship between BH4 and cell death is not well understood yet. The possibility that the cofactor directly influences cell viability has not been excluded in previous studies when modulating BH4-producing enzymes. Future Directions: The importance of cellular BH4 variations and BH4 biosynthetic enzymes to cell function and viability makes it essential to better characterize temporal changes, cofactor activity, and the influence on redox status, which in turn would help develop novel therapies. Antioxid. Redox Signal. 37, 171-183.

Measurement of Tetrahydrobiopterin in Animal Tissue Samples by HPLC with Electrochemical Detection-Protocol Optimization and Pitfalls

Tetrahydrobiopterin (BH4) is an essential cofactor of all nitric oxide synthase isoforms, thus determination of BH4 levels can provide important mechanistic insight into diseases. We established a protocol for high-performance liquid chromatography/electrochemical detection (HPLC/ECD)-based determination of BH4 in tissue samples. We first determined the optimal storage and work-up conditions for authentic BH4 and its oxidation product dihydrobiopterin (BH2) under various conditions (pH, temperature, presence of antioxidants, metal chelators, and storage time). We then applied optimized protocols for detection of BH4 in tissues of septic (induced by lipopolysaccharide [LPS]) rats. BH4 standards in HCl are stabilized by addition of 1,4-dithioerythritol (DTE) and diethylenetriaminepentaacetic acid (DTPA), while HCl was sufficient for BH2 standard stabilization. Overnight storage of BH4 standard solutions at room temperature in HCl without antioxidants caused complete loss of BH4 and the formation of BH2. We further optimized the protocol to separate ascorbate and the BH4 tissue sample and found a significant increase in BH4 in the heart and kidney as well as higher BH4 levels by trend in the brain of septic rats compared to control rats. These findings correspond to reports on augmented nitric oxide and BH4 levels in both animals and patients with septic shock.

Priapism caused by partial deficiency of tetrahydrobiopterin through hypofunction of the sympathetic neurons in sepiapterin reductase gene-disrupted mice

6R-L-erythro-5,6,7,8-tetrahydrobiopterin (BH4) is an essential cofactor for aromatic L-amino acid hydroxylases, including tyrosine hydroxylase (TH), alkylglycerol monooxygenase, and three types of nitric oxide (NO) synthases (NOS). Sepiapterin reductase (SPR) catalyzes the third step of BH4 biosynthesis. SPR gene-disrupted (Spr-/- ) mice exhibit a dystonic posture, low body weight, hyperphenylalaninemia, and unstable hypertension with endothelial dysfunction. In this study, we found that Spr-/- mice suffered from a high incidence of severe priapism. Their erections persisted for months. The biopterin, BH4, and norepinephrine contents, and TH protein levels in the penile tissue of Spr-/- mice without and with priapism were significantly reduced compared to those of Spr+/+ mice. In contrast, their neural NOS (nNOS) protein levels were increased, and the cyclic guanosine monophosphate (cGMP) levels were remarkably elevated in the penises of Spr-/- mice with priapism. The symptoms were relieved by repeated administration of BH4. The biopterin, BH4, and norepinephrine contents were increased in penile homogenates from BH4-supplemented Spr-/- mice, and the TH protein levels tended to increase, and their nitrite plus nitrate levels were significantly lower than those of vehicle-treated Spr-/- mice and were approximately the same as vehicle- and BH4-supplemented Spr+/+ mice. Thus, we deduced that the priapism of Spr-/- mice is primarily caused by hypofunction of the sympathetic neurons due to cofactor depletion and the loss of TH protein and, further, dysregulation of the NO/cGMP signaling pathway, which would be caused by disinhibition of nNOS-containing neurons and/or abnormal catabolism of cyclic nucleotides is suggested.

No effect of acute tetrahydrobiopterin (BH4) supplementation on vascular dysfunction in the old

As a deficiency in tetrahydrobiopterin (BH4), a cofactor for endothelial nitric oxide synthase, has been implicated in the age-related decline in vascular function, this study aimed to determine the impact of acute BH4 supplementation on flow-mediated vasodilation (FMD) in old adults. Two approaches were used: 1) A multiday, double-blind, placebo-controlled, crossover design measuring, FMD [ΔFMD (mm), %FMD (%)] and shear rate area under the curve (SR AUC) in nine old subjects (73 ± 8 yr) with either placebo (placebo) or BH4 (≈10 mg/kg, post), and 2) a single experimental day measuring FMD in an additional 13 old subjects (74 ± 7 yr) prior to (pre) and 4.5 h after ingesting BH4 (≈10 mg/kg). With the first experimental approach, acute BH4 intake did not significantly alter FMD (ΔFMD: 0.17 ± 0.03 vs. 0.13 ± 0.02 mm; %FMD: 3.3 ± 0.61 vs. 2.9 ± 0.4%) or SR AUC (30,280 ± 4,428 vs. 37,877 ± 9,241 s-1) compared with placebo. Similarly, with the second approach, BH4 did not significantly alter FMD (ΔFMD: 0.09 ± 0.02 vs. 0.12 ± 0.03 mm; %FMD: 2.2 ± 0.6 vs. 2.9 ± 0.6%) or SR AUC (37,588 ± 6,753 vs. 28,996 ± 3,735 s-1) compared with pre. Moreover, when the two data sets were combined, resulting in a greater sample size, there was still no evidence of an effect of BH4 on vascular function in these old subjects. Importantly, both plasma BH4 and 7,8-dihydrobiopterin (BH2), the oxidized form of BH4, increased significantly with acute BH4 supplementation. Consequently, the ratio of BH4/BH2, recognized to impact vascular function, was unchanged. Thus, acute BH4 supplementation does not correct vascular dysfunction in the old.NEW & NOTEWORTHY Despite two different experimental approaches, acute BH4 supplementation did not affect vascular function in older adults, as measured by flow-mediated vasodilation. Plasma levels of both BH4 and BH2, the BH4 oxidized form, significantly increased after acute BH4 supplementation, resulting in an unchanged ratio of BH4/BH2, a key determining factor for endothelial nitric oxide synthase coupling. Therefore, likely due to the elevated oxidative stress with advancing age, acute BH4 supplementation does not correct vascular dysfunction in the old.

Endogenous Hemoprotein-Dependent Signaling Pathways of Nitric Oxide and Nitrite

Interdisciplinary research at the interface of chemistry, physiology, and biomedicine have uncovered pivotal roles of nitric oxide (NO) as a signaling molecule that regulates vascular tone, platelet aggregation, and other pathways relevant to human health and disease. Heme is central to physiological NO signaling, serving as the active site for canonical NO biosynthesis in nitric oxide synthase (NOS) enzymes and as the highly selective NO binding site in the soluble guanylyl cyclase receptor. Outside of the primary NOS-dependent biosynthetic pathway, other hemoproteins, including hemoglobin and myoglobin, generate NO via the reduction of nitrite. This auxiliary hemoprotein reaction unlocks a "second axis" of NO signaling in which nitrite serves as a stable NO reservoir. In this Forum Article, we highlight these NO-dependent physiological pathways and examine complex chemical and biochemical reactions that govern NO and nitrite signaling in vivo. We focus on hemoprotein-dependent reaction pathways that generate and consume NO in the presence of nitrite and consider intermediate nitrogen oxides, including NO2, N2O3, and S-nitrosothiols, that may facilitate nitrite-based signaling in blood vessels and tissues. We also discuss emergent therapeutic strategies that leverage our understanding of these key reaction pathways to target NO signaling and treat a wide range of diseases.

Metastatic Melanoma Progression Is Associated with Endothelial Nitric Oxide Synthase Uncoupling Induced by Loss of eNOS:BH4 Stoichiometry

Melanoma is the most aggressive type of skin cancer due to its high capability of developing metastasis and acquiring chemoresistance. Altered redox homeostasis induced by increased reactive oxygen species is associated with melanomagenesis through modulation of redox signaling pathways. Dysfunctional endothelial nitric oxide synthase (eNOS) produces superoxide anion (O2-•) and contributes to the establishment of a pro-oxidant environment in melanoma. Although decreased tetrahydrobiopterin (BH4) bioavailability is associated with eNOS uncoupling in endothelial and human melanoma cells, in the present work we show that eNOS uncoupling in metastatic melanoma cells expressing the genes from de novo biopterin synthesis pathway Gch1, Pts, and Spr, and high BH4 concentration and BH4:BH2 ratio. Western blot analysis showed increased expression of Nos3, altering the stoichiometry balance between eNOS and BH4, contributing to NOS uncoupling. Both treatment with L-sepiapterin and eNOS downregulation induced increased nitric oxide (NO) and decreased O2• levels, triggering NOS coupling and reducing cell growth and resistance to anoikis and dacarbazine chemotherapy. Moreover, restoration of eNOS activity impaired tumor growth in vivo. Finally, NOS3 expression was found to be increased in human metastatic melanoma samples compared with the primary site. eNOS dysfunction may be an important mechanism supporting metastatic melanoma growth and hence a potential target for therapy.

The Role of the BH4 Cofactor in Nitric Oxide Synthase Activity and Cancer Progression: Two Sides of the Same Coin

Cancer development is associated with abnormal proliferation, genetic instability, cell death resistance, metabolic reprogramming, immunity evasion, and metastasis. These alterations are triggered by genetic and epigenetic alterations in genes that control cell homeostasis. Increased reactive oxygen and nitrogen species (ROS, RNS) induced by different enzymes and reactions with distinct molecules contribute to malignant transformation and tumor progression by modifying DNA, proteins, and lipids, altering their activities. Nitric oxide synthase plays a central role in oncogenic signaling modulation and redox landscape. Overexpression of the three NOS isoforms has been found in innumerous types of cancer contributing to tumor growth and development. Although the main function of NOS is the production of nitric oxide (NO), it can be a source of ROS in some pathological conditions. Decreased tetrahydrobiopterin (BH4) cofactor availability is involved in NOS dysfunction, leading to ROS production and reduced levels of NO. The regulation of NOSs by BH4 in cancer is controversial since BH4 has been reported as a pro-tumoral or an antitumoral molecule. Therefore, in this review, the role of BH4 in the control of NOS activity and its involvement in the capabilities acquired along tumor progression of different cancers was described.

Decreased Expression and Uncoupling of Endothelial Nitric Oxide Synthase in the Cerebral Cortex of Rats with Thioacetamide-Induced Acute Liver Failure

Acute liver failure (ALF) is associated with deregulated nitric oxide (NO) signaling in the brain, which is one of the key molecular abnormalities leading to the neuropsychiatric disorder called hepatic encephalopathy (HE). This study focuses on the effect of ALF on the relatively unexplored endothelial NOS isoform (eNOS). The cerebral prefrontal cortices of rats with thioacetamide (TAA)-induced ALF showed decreased eNOS expression, which resulted in an overall reduction of NOS activity. ALF also decreased the content of the NOS cofactor, tetrahydro-L-biopterin (BH4), and evoked eNOS uncoupling (reduction of the eNOS dimer/monomer ratio). The addition of the NO precursor L-arginine in the absence of BH4 potentiated ROS accumulation, whereas nonspecific NOS inhibitor L-NAME or EDTA attenuated ROS increase. The ALF-induced decrease of eNOS content and its uncoupling concurred with, and was likely causally related to, both increased brain content of reactive oxidative species (ROS) and decreased cerebral cortical blood flow (CBF) in the same model.

How does ascorbate improve endothelial dysfunction? - A computational analysis

Low levels of ascorbate (Asc) are observed in cardiovascular and neurovascular diseases. Asc has therapeutic potential for the treatment of endothelial dysfunction, which is characterized by a reduction in nitric oxide (NO) bioavailability and increased oxidative stress in the vasculature. However, the potential mechanisms remain poorly understood for the Asc mitigation of endothelial dysfunction. In this study, we developed an endothelial cell based computational model integrating endothelial cell nitric oxide synthase (eNOS) biochemical pathway with downstream reactions and interactions of oxidative stress, tetrahydrobiopterin (BH4) synthesis and biopterin ratio ([BH4]/[TBP]), Asc and glutathione (GSH). We quantitatively analyzed three Asc mediated mechanisms that are reported to improve/maintain endothelial cell function. The mechanisms include the reduction of •BH3 to BH4, direct scavenging of superoxide (O2•-) and peroxynitrite (ONOO-) and increasing eNOS activity. The model predicted that Asc at 0.1-100 μM concentrations improved endothelial cell NO production, total biopterin and biopterin ratio in a dose dependent manner and the extent of cellular oxidative stress. Asc increased BH4 availability and restored eNOS coupling under oxidative stress conditions. Asc at concentrations of 1-10 mM reduced O2•- and ONOO- levels and could act as an antioxidant. We predicted that glutathione peroxidase and peroxiredoxin in combination with GSH and Asc can restore eNOS coupling and NO production under oxidative stress conditions. Asc supplementation may be used as an effective therapeutic strategy when BH4 levels are depleted. This study provides detailed understanding of the mechanism responsible and the optimal cellular Asc levels for improvement in endothelial dysfunction.

Sickle Cell Disease: Role of Oxidative Stress and Antioxidant Therapy

Sickle cell disease (SCD) is the most common hereditary disorder of hemoglobin (Hb), which affects approximately a million people worldwide. It is characterized by a single nucleotide substitution in the β-globin gene, leading to the production of abnormal sickle hemoglobin (HbS) with multi-system consequences. HbS polymerization is the primary event in SCD. Repeated polymerization and depolymerization of Hb causes oxidative stress that plays a key role in the pathophysiology of hemolysis, vessel occlusion and the following organ damage in sickle cell patients. For this reason, reactive oxidizing species and the (end)-products of their oxidative reactions have been proposed as markers of both tissue pro-oxidant status and disease severity. Although more studies are needed to clarify their role, antioxidant agents have been shown to be effective in reducing pathological consequences of the disease by preventing oxidative damage in SCD, i.e., by decreasing the oxidant formation or repairing the induced damage. An improved understanding of oxidative stress will lead to targeted antioxidant therapies that should prevent or delay the development of organ complications in this patient population.

Sulfamethoxazole drug stress upregulates antioxidant immunomodulatory metabolites in Escherichia coli

Escherichia coli is an important model organism in microbiology and a prominent member of the human microbiota¹. Environmental isolates readily colonize the gastrointestinal tract of humans and other animals, and they can serve diverse probiotic, commensal and pathogenic roles in the host^2-4. Although certain strains have been associated with the severity of inflammatory bowel disease (IBD)^2,5, the diverse immunomodulatory phenotypes remain largely unknown at the molecular level. Here, we decode a previously unknown E. coli metabolic pathway that produces a family of hybrid pterin-phenylpyruvate conjugates, which we named the colipterins. The metabolites are upregulated by subinhibitory levels of the antifolate sulfamethoxazole, which is used to treat infections including in patients with IBD^6,7. The genes folX/M and aspC/tyrB involved in monapterin biosynthesis^8-10 and aromatic amino acid transamination,¹¹ respectively, were required to initiate the colipterin pathway. We show that the colipterins are antioxidants, harbour diverse immunological activities in primary human tissues, activate anti-inflammatory interleukin-10 and improve colitis symptoms in a colitis mouse model. Our study defines an antifolate stress response in E. coli and links its associated metabolites to a major immunological marker of IBD.

Experimental and Clinical Evidence of Endothelial Dysfunction in Inflammatory Bowel Disease

The endothelium has a crucial role in proper hemodynamics. Inflammatory bowel disease (IBD) is mainly a chronic inflammatory condition of the gastrointestinal tract. However, considerable evidence points to high cardiovascular risk in patients with IBD. This review positions the basic mechanisms of endothelial dysfunction in the IBD setting (both clinical and experimental). Furthermore, we review the main effects of drugs used to treat IBD in endothelial (dys)function. Moreover, we leave challenging points for enlarging the therapeutic arsenal for IBD with new or repurposed drugs that target endothelial dysfunction besides inflammation.

Neuronal vulnerability to fetal hypoxia-reoxygenation injury and motor deficit development relies on regional brain tetrahydrobiopterin levels

Hypertonia is pathognomonic of cerebral palsy (CP), often caused by brain injury before birth. To understand the early driving events of hypertonia, we utilized magnetic resonance imaging (MRI) assessment of early critical brain injury in rabbit fetuses (79% term) that will predict hypertonia after birth following antenatal hypoxia-ischemia. We examined if individual variations in the tetrahydrobiopterin cofactor in the parts of the brain controlling motor function could indicate a role in specific damage to motor regions and disruption of circuit integration as an underlying mechanism for acquiring motor disorders, which has not been considered before. The rabbit model mimicked acute placental insufficiency and used uterine ischemia at a premature gestation. MRI during the time of hypoxia-ischemia was used to differentiate which individual fetal brains would become hypertonic. Four brain regions collected immediately after hypoxia-ischemia or 48 h later were analyzed in a blinded fashion. Age-matched sham-operated animals were used as controls. Changes in the reactive nitrogen species and gene expression of the tetrahydrobiopterin biosynthetic enzymes in brain regions were also studied. We found that a combination of low tetrahydrobiopterin content in the cortex, basal ganglia, cerebellum, and thalamus brain regions, but not a unique low threshold of tetrahydrobiopterin, contributed etiologically to hypertonia. The biggest contribution was from the thalamus. Evidence for increased reactive nitrogen species was found in the cortex. By 48 h, tetrahydrobiopterin and gene expression levels in the different parts of the brain were not different between MRI stratified hypertonia and non-hypertonia groups. Sepiapterin treatment given to pregnant dams immediately after hypoxia-ischemia ameliorated hypertonia and death. We conclude that a developmental tetrahydrobiopterin variation is necessary with fetal hypoxia-ischemia and is critical for disrupting normal motor circuits that develop into hypertonia. The possible mechanistic pathway involves reactive nitrogen species.

A theoretical study of 5,6,7,8-tetrahydro-6-hydroxymethylpterin: insight into intrinsic photoreceptor properties of 6-substituted tetrahydropterins

Tetrahydropterins are essential biological cofactors, which play a crucial role in DNA and RNA syntheses, NO synthesis, hydroxylation of aromatic amino acids, etc. In the last few years, it has been shown that 6-substituted "unconjugated" tetrahydropterins can also play a photoreceptor chromophoric role in plants and cyanobacteria. However, the nature of the initial light signal transduction act in which H4pterins participate is unknown. Our quantum chemical calculations have shown the possibility of the fast internal conversion of excited states of H4pterins. The potential energy surface scan along the 1ππ* state shows no energy barrier leading to 1ππ*/S0 conical intersection, this explains the absence of fluorescence for H4pterins. Other trajectories of the internal conversion relate to the stretching vibrations of the N-H bonds of the pyrimidine ring for the Rydberg state. The presence of several trajectories of nonradiative quenching of the photoexcited singlet states provides the photostability of the molecule. It was demonstrated for the first time that the nature of the excited states of H4pterins is similar to the nature of the excited states of guanine.

Sources of Vascular Nitric Oxide and Reactive Oxygen Species and Their Regulation

Nitric oxide (NO) is a small free radical with critical signaling roles in physiology and pathophysiology. The generation of sufficient NO levels to regulate the resistance of the blood vessels and hence the maintenance of adequate blood flow is critical to the healthy performance of the vasculature. A novel paradigm indicates that classical NO synthesis by dedicated NO synthases is supplemented by nitrite reduction pathways under hypoxia. At the same time, reactive oxygen species (ROS), which include superoxide and hydrogen peroxide, are produced in the vascular system for signaling purposes, as effectors of the immune response, or as byproducts of cellular metabolism. NO and ROS can be generated by distinct enzymes or by the same enzyme through alternate reduction and oxidation processes. The latter oxidoreductase systems include NO synthases, molybdopterin enzymes, and hemoglobins, which can form superoxide by reduction of molecular oxygen or NO by reduction of inorganic nitrite. Enzymatic uncoupling, changes in oxygen tension, and the concentration of coenzymes and reductants can modulate the NO/ROS production from these oxidoreductases and determine the redox balance in health and disease. The dysregulation of the mechanisms involved in the generation of NO and ROS is an important cause of cardiovascular disease and target for therapy. In this review we will present the biology of NO and ROS in the cardiovascular system, with special emphasis on their routes of formation and regulation, as well as the therapeutic challenges and opportunities for the management of NO and ROS in cardiovascular disease.

New Therapeutic Implications of Endothelial Nitric Oxide Synthase (eNOS) Function/Dysfunction in Cardiovascular Disease

The Global Burden of Disease Study identified cardiovascular risk factors as leading causes of global deaths and life years lost. Endothelial dysfunction represents a pathomechanism that is associated with most of these risk factors and stressors, and represents an early (subclinical) marker/predictor of atherosclerosis. Oxidative stress is a trigger of endothelial dysfunction and it is a hall-mark of cardiovascular diseases and of the risk factors/stressors that are responsible for their initiation. Endothelial function is largely based on endothelial nitric oxide synthase (eNOS) function and activity. Likewise, oxidative stress can lead to the loss of eNOS activity or even “uncoupling” of the enzyme by adverse regulation of well-defined “redox switches” in eNOS itself or up-/down-stream signaling molecules. Of note, not only eNOS function and activity in the endothelium are essential for vascular integrity and homeostasis, but also eNOS in perivascular adipose tissue plays an important role for these processes. Accordingly, eNOS protein represents an attractive therapeutic target that, so far, was not pharmacologically exploited. With our present work, we want to provide an overview on recent advances and future therapeutic strategies that could be used to target eNOS activity and function in cardiovascular (and other) diseases, including life style changes and epigenetic modulations. We highlight the redox-regulatory mechanisms in eNOS function and up- and down-stream signaling pathways (e.g., tetrahydrobiopterin metabolism and soluble guanylyl cyclase/cGMP pathway) and their potential pharmacological exploitation.

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.

Inorganic Polyphosphate Is Essential for Salmonella Typhimurium Virulence and Survival in Dictyostelium discoideum

Inorganic polyphosphate (polyP) deficiency in enteric bacterial pathogens reduces their ability to invade and establish systemic infections in different hosts. For instance, inactivation of the polyP kinase gene (ppk) encoding the enzyme responsible for polyP biosynthesis reduces invasiveness and intracellular survival of Salmonella enterica serovar Typhimurium (S. Typhimurium) in epithelial cells and macrophages in vitro. In addition, the virulence in vivo of a S. Typhimurium Δppk mutant is significantly reduced in a murine infection model. In spite of these observations, the role played by polyP during the Salmonella-host interaction is not well understood. The social amoeba Dictyostelium discoideum has proven to be a useful model for studying relevant aspects of the host-pathogen interaction. In fact, many intracellular pathogens can survive within D. discoideum cells using molecular mechanisms also required to survive within macrophages. Recently, we established that S. Typhimurium is able to survive intracellularly in D. discoideum and identified relevant genes linked to virulence that are crucial for this process. The aim of this study was to determine the effect of a polyP deficiency in S. Typhimurium during its interaction with D. discoideum. To do this, we evaluated the intracellular survival of wild-type and Δppk strains of S. Typhimurium in D. discoideum and the ability of these strains to delay the social development of the amoeba. In contrast to the wild-type strain, the Δppk mutant was unable to survive intracellularly in D. discoideum and enabled the social development of the amoeba. Both phenotypes were complemented using a plasmid carrying a copy of the ppk gene. Next, we simultaneously evaluated the proteomic response of both S. Typhimurium and D. discoideum during host-pathogen interaction via global proteomic profiling. The analysis of our results allowed the identification of novel molecular signatures that give insight into Salmonella-Dictyostelium interaction. Altogether, our results indicate that inorganic polyP is essential for S. Typhimurium virulence and survival in D. discoideum. In addition, we have validated the use of global proteomic analyses to simultaneously evaluate the host-pathogen interaction of S. Typhimurium and D. discoideum. Furthermore, our infection assays using these organisms can be exploited to screen for novel anti-virulence molecules targeting inorganic polyP biosynthesis.

Chronic Kidney Disease and Disproportionally Increased Cardiovascular Damage: Does Oxidative Stress Explain the Burden?

Chronic kidney disease (CKD) patients are among the groups at the highest risk for cardiovascular disease and significantly shortened remaining lifespan. CKD enhances oxidative stress in the organism with ensuing cardiovascular damage. Oxidative stress in uremia is the consequence of higher reactive oxygen species (ROS) production, whereas attenuated clearance of pro-oxidant substances and impaired antioxidant defenses play a complementary role. The pathophysiological mechanism underlying the increased ROS production in CKD is at least partly mediated by upregulation of the intrarenal angiotensin system. Enhanced oxidative stress in the setting of the uremic milieu promotes enzymatic modification of circulating lipids and lipoproteins, protein carbamylation, endothelial dysfunction via disruption of nitric oxide (NO) pathways, and activation of inflammation, thus accelerating atherosclerosis. Left ventricular hypertrophy (LVH) and heart failure are hallmarks of CKD. NADPH oxidase activation, xanthine oxidase, mitochondrial dysfunction, and NO-ROS are the main oxidative pathways leading to LVH and the cardiorenal syndrome. Finally, a subset of antioxidant enzymes, the paraoxonases (PON), deserves special attention due to abundant clinical evidence accumulated regarding reduced serum PON1 activity in CKD as a contributor to the increased burden of cardiovascular disease. Future, meticulously designed studies are needed to assess the effects of antioxidant therapy on patients with CKD.

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.

Tetrahydrobiopterin in antenatal brain hypoxia-ischemia-induced motor impairments and cerebral palsy

Antenatal brain hypoxia-ischemia, which occurs in cerebral palsy, is considered a significant cause of motor impairments in children. The mechanisms by which antenatal hypoxia-ischemia causes brain injury and motor deficits still need to be elucidated. Tetrahydrobiopterin is an important enzyme cofactor that is necessary to produce neurotransmitters and to maintain the redox status of the brain. A genetic deficiency of this cofactor from mutations of biosynthetic or recycling enzymes is a well-recognized factor in the development of childhood neurological disorders characterized by motor impairments, developmental delay, and encephalopathy. Experimental hypoxia-ischemia causes a decline in the availability of tetrahydrobiopterin in the immature brain. This decline coincides with the loss of brain function, suggesting this occurrence contributes to neuronal dysfunction and motor impairments. One possible mechanism linking tetrahydrobiopterin deficiency, hypoxia-ischemia, and neuronal injury is oxidative injury. Evidence of the central role of the developmental biology of tetrahydrobiopterin in response to hypoxic ischemic brain injury, especially the development of motor deficits, is discussed.

Astragaloside IV improves the isoproterenol-induced vascular dysfunction via attenuating eNOS uncoupling-mediated oxidative stress and inhibiting ROS-NF-κB pathways

OBJECTIVE

Oxidative stress and inflammation are regarded as two important triggers of endothelial dysfunction and play pivotal role in progression of vascular damage associated with cardiac hypertrophy. Our previous studies demonstrated that astragaloside IV (AsIV) could protect against cardiac hypertrophy in rats induced by isoproterenol (Iso), but its effects on the aorta are not known. In present study, we aimed to assess the effects of AsIV on Isoinduced vascular dysfunction.

METHODS

Sprague-Dawley (SD) rats were treated with Iso (10mg/kg/d) alone or in combination with AsIV (50mg/kg/d).

RESULTS

Compared with Isotreated alone, AsIV significantly reduced the ratios of heart weight/body weight and left ventricular weight/body weight. AsIV ameliorated the increased vasoconstriction response to phenylephrine induced by Iso and suppressed superoxide anion generation in rat aorta, increased endothelial nitric oxide synthase (eNOS) dimer/monomer ratio and its critical cofactor tetrahydrobiopterin (BH4) content in aorta as well as the NO production in the serum, reduced the plasmatic peroxynitrite (ONOO-). Moreover, in contrast with Isotreatment alone, AsIV decreased the ratio of nuclear-to-cytosolic protein expression of the NF-κB p65 subunit while enhanced its inhibited protein expression of IκB-α, down-regulated mRNA expression of IL-1β, IL-6 and TNF-α of the aorta.

CONCLUSIONS

The present study suggested that AsIV protects against Isoinduced vascular dysfunction probably via attenuating eNOS uncoupling-mediated oxidative stress and inhibiting ROS-NF-κB pathways.

Jak2/Stat1 pathway mediated tetrahydrobiopterin up-regulation contributes to nitric oxide overproduction in high-glucose cultured rat mesangial cells

Nitric oxide (NO) is crucial for the progression of early diabetic nephropathy (DN). It is important to clarify the mechanism for the production of NO in mesangial cells (MCs). In this study, the amounts/activities of related factors such as reactive oxygen species (ROS), NO, 3 isoforms of nitric oxide synthase (NOS), tetrahydrobiopterin (BH4), GTP cyclohydrolase I (GTPCH I), Jak2, and Stat1 were determined using high-glucose cultured rat MCs. The results showed that the production of BH4 under oxidative stress was strongly stimulated by its rate-limiting enzyme GTP cyclohydrolase, which increased the expression and activity of inducible NOS to facilitate NO synthesis. Furthermore, the relative quantities of activated-Jak2 and activated-Stat1 were increased. Therefore, Jak2/Stat1 pathway mediated BH4 up-regulation can contribute to excessive NO in high-glucose cultured MCs. Our results will be helpful for screening new targets to improve the therapy for early DN.

Cell type-specific recycling of tetrahydrobiopterin by dihydrofolate reductase explains differential effects of 7,8-dihydrobiopterin on endothelial nitric oxide synthase uncoupling

(6R)-5,6,7,8-Tetrahydro-L-biopterin (BH4) availability regulates nitric oxide and superoxide formation by endothelial nitric oxide synthase (eNOS). At low BH4 or low BH4 to 7,8-dihydrobiopterin (BH2) ratios the enzyme becomes uncoupled and generates superoxide at the expense of NO. We studied the effects of exogenously added BH2 on intracellular BH4/BH2 ratios and eNOS activity in different types of endothelial cells. Incubation of porcine aortic endothelial cells with BH2 increased BH4/BH2 ratios from 8.4 (controls) and 0.5 (BH4-depleted cells) up to ~20, demonstrating efficient reduction of BH2. Uncoupled eNOS activity observed in BH4-depleted cells was prevented by preincubation with BH2. Recycling of BH4 was much less efficient in human endothelial cells isolated from umbilical veins or derived from dermal microvessels (HMEC-1 cells), which exhibited eNOS uncoupling and low BH4/BH2 ratios under basal conditions and responded to exogenous BH2 with only moderate increases in BH4/BH2 ratios. The kinetics of dihydrofolate reductase-catalyzed BH4 recycling in endothelial cytosols showed that the apparent BH2 affinity of the enzyme was 50- to 300-fold higher in porcine than in human cell preparations. Thus, the differential regulation of eNOS uncoupling in different types of endothelial cells may be explained by striking differences in the apparent BH2 affinity of dihydrofolate reductase.

Mitochondria-targeted spin traps: synthesis, superoxide spin trapping, and mitochondrial uptake

Development of reliable methods and site-specific detection of free radicals is an active area of research. Here, we describe the synthesis and radical-trapping properties of new derivatives of DEPMPO and DIPPMPO, bearing a mitochondria-targeting triphenylphosphonium cationic moiety or guanidinium cationic group. All of the spin traps prepared have been observed to efficiently trap superoxide radical anions in a cell-free system. The superoxide spin adducts exhibited similar spectral properties, indicating no significant differences in the geometry of the cyclic nitroxide moieties of the spin adducts. The superoxide adduct stability was measured and observed to be highest (t1/2 = 73 min) for DIPPMPO nitrone linked to triphenylphosphonium moiety via a short carbon chain (Mito-DIPPMPO). The experimental results and DFT quantum chemical calculations indicate that the cationic property of the triphenylphosphonium group may be responsible for increased superoxide trapping efficiency and adduct stability of Mito-DIPPMPO, as compared to the DIPPMPO spin trap. The studies of uptake of the synthesized traps into isolated mitochondria indicated the importance of both cationic and lipophilic properties, with the DEPMPO nitrone linked to the triphenylphosphonium moiety via a long carbon chain (Mito10-DEPMPO) exhibiting the highest mitochondrial uptake. We conclude that, of the synthesized traps, Mito-DIPPMPO and Mito10-DEPMPO are the best candidates for potential mitochondria-specific spin traps for use in biologically relevant systems.

Developmental susceptibility of neurons to transient tetrahydrobiopterin insufficiency and antenatal hypoxia-ischemia in fetal rabbits

Tetrahydrobiopterin (BH4) is important for normal brain development as congenital BH4 deficiencies manifest movement disorders at various childhood ages. BH4 transitions from very low levels in fetal brains to higher "adult" levels postnatally, with the highest levels in the thalamus. Maternal supplementation with the BH4 precursor sepiapterin reduces postnatal motor deficits and perinatal deaths after 40-min fetal hypoxia-ischemia (HI) at 70% gestation, suggesting that brain BH4 is important in improving function after HI. We tested the hypothesis that the intrinsically low concentrations of BH4 made fetal neurons vulnerable to added insults. Brains were obtained from naïve fetal rabbits or after 40-min HI, at 70% (E22) and 92% gestation (E29). Neuronal cultures were prepared from basal ganglia, cortex, and thalamus, regions with different intrinsic levels of BH4. Cultures were grown with or without added BH4 for 48h. Cell survival and mitochondrial function were determined by flow cytometry. At E22, thalamic cells had the lowest survival rate in a BH4-free milieu, in both control and HI groups, whereas BH4 supplementation ex vivo increased neuronal survival only in HI cells. Neuronal survival was similar in all regions without BH4 at E29. BH4 supplementation increased cell survival and cells with intact mitochondrial membrane potential, from basal ganglia and cortex, but not thalamus. After E29 HI, however, the benefit of BH4 was limited to cortical neurons. We conclude that BH4 is important for fetal neuronal survival after HI especially in the premature thalamus. Supplementation of BH4 has a greater benefit at an earlier gestational age.

Does vitamin C enhance nitric oxide bioavailability in a tetrahydrobiopterin-dependent manner? In vitro, in vivo and clinical studies

Ascorbate (Asc) has been shown to increase nitric oxide (NO) bioavailability and thereby improve endothelial function in patients showing signs of endothelial dysfunction. Tetrahydrobiopterin (BH₄) is a co-factor of endothelial nitric oxide synthase (eNOS) which may easily become oxidized to the inactive form dihydrobiopterin (BH₂). Asc may increase NO bioavailability by a number of mechanisms involving BH₄ and eNOS. Asc increases BH₄ bioavailability by either reducing oxidized BH₄ or preventing BH₄ from becoming oxidized in the first place. Asc could also increase NO bioavailability in a BH₄-independent manner by increasing eNOS activity by changing its phosphorylation and S-nitrosylation status or by upregulating eNOS expression. In this review, we discuss the putative mechanisms by which Asc may increase NO bioavailability through its interactions with BH₄ and eNOS.

Mitochondrial redox signaling: Interaction of mitochondrial reactive oxygen species with other sources of oxidative stress

SIGNIFICANCE

Oxidative stress is a well established hallmark of cardiovascular disease and there is strong evidence for a causal role of reactive oxygen and nitrogen species (RONS) therein.

RECENT ADVANCES

Improvement of cardiovascular complications by genetic deletion of RONS producing enzymes and overexpression of RONS degrading enzymes proved the involvement of these species in cardiovascular disease at a molecular level. Vice versa, overexpression of RONS producing enzymes as well as deletion of antioxidant enzymes was demonstrated to aggravate cardiovascular complications.

CRITICAL ISSUES

With the present overview we present and discuss different pathways how mitochondrial RONS interact (crosstalk) with other sources of oxidative stress, namely NADPH oxidases, xanthine oxidase and an uncoupled nitric oxide synthase. The potential mechanisms of how this crosstalk proceeds are discussed in detail. Several examples from the literature are summarized (including hypoxia, angiotensin II mediated vascular dysfunction, cellular starvation, nitrate tolerance, aging, hyperglycemia, β-amyloid stress and others) and the underlying mechanisms are put together to a more general concept of redox-based activation of different sources of RONS via enzyme-specific "redox switches". Mitochondria play a key role in this concept providing redox triggers for oxidative damage in the cardiovascular system but also act as amplifiers to increase the burden of oxidative stress.

FUTURE DIRECTIONS

Based on these considerations, the characterization of the role of mitochondrial RONS formation in cardiac disease as well as inflammatory processes but also the role of mitochondria as potential therapeutic targets in these pathophysiological states should be addressed in more detail in the future.

Oxidative stress in sickle cell disease: an overview of erythrocyte redox metabolism and current antioxidant therapeutic strategies

Erythrocytes have an environment of continuous pro-oxidant generation due to the presence of hemoglobin (Hb), which represents an additional and quantitatively significant source of superoxide (O2(-)) generation in biological systems. To counteract oxidative stress, erythrocytes have a self-sustaining antioxidant defense system. Thus, red blood cells uniquely function to protect Hb via a selective barrier allowing gaseous and other ligand transport as well as providing antioxidant protection not only to themselves but also to other tissues and organs in the body. Sickle hemoglobin molecules suffer repeated polymerization/depolymerization generating greater amounts of reactive oxygen species, which can lead to a cyclic cascade characterized by blood cell adhesion, hemolysis, vaso-occlusion, and ischemia-reperfusion injury. In other words, sickle cell disease is intimately linked to a pathophysiologic condition of multiple sources of pro-oxidant processes with consequent chronic and systemic oxidative stress. For this reason, newer therapeutic agents that can target oxidative stress may constitute a valuable means for preventing or delaying the development of organ complications.

Bioluminescent detection of peroxynitrite with a boronic acid-caged luciferin

Peroxynitrite, a highly reactive biological oxidant, is formed under pathophysiologic conditions from the diffusion-limited reaction of nitric oxide and superoxide radical anion. Peroxynitrite has been implicated as the mediator of nitric oxide toxicity in many diseases and as an important signaling disrupting molecule (L. Liaudet et al., Front. Biosci.14, 4809-4814, 2009) [1]. Biosensors effective at capturing peroxynitrite in a specific and fast enough manner for detection, along with readouts compatible with in vivo studies, are lacking. Here we report that the boronic acid-based bioluminescent system PCL-1 (peroxy-caged luciferin-1), previously reported as a chemoselective sensor for hydrogen peroxide (G.C. Van de Bittner et al., Proc. Natl. Acad. Sci. USA107, 21316-21321, 2010) [2], reacts with peroxynitrite stoichiometrically with a rate constant of 9.8±0.3×10(5)M(-1)s(-1) and a bioluminescence detection limit of 16nM, compared to values of 1.2±0.3M(-1)s(-1) and 231nM for hydrogen peroxide. Further, we demonstrate bioluminescent detection of peroxynitrite in the presence of physiological competitors: carbon dioxide, glutathione, albumin, and catalase. We also demonstrate the utility of this method to assess peroxynitrite formation in mammalian cells by measuring peroxynitrite generated under normal culture conditions after stimulation of macrophages with bacterial endotoxin lipopolysaccharide. Thus, the PCL-1 method for measuring peroxynitrite generation shows superior selectivity over other oxidants under in vivo conditions.

Evidence for therapeutic intervention in the prevention of cerebral palsy: hope from animal model research

Knowledge translation, as defined by the Canadian Institute of Health Research, is defined as the exchange, synthesis, and ethically sound application of knowledge--within a complex system of interactions among researchers and users--to accelerate the capture of the benefits of research through improved health, more effective services and products, and a strengthened healthcare system. The requirement for this to occur lies in the ability to continue to determine mechanistic actions at the molecular level, to understand how they fit at the in vitro and in vivo levels, and for disease states, to determine their safety, efficacy, and long-term potential at the preclinical animal model level. In this regard, particularly as it relates to long-term disabilities such as cerebral palsy that begin in utero, but only express their full effect in adulthood, animal models must be used to understand and rapidly evaluate mechanisms of injury and therapeutic interventions. In this review, we hope to provide the reader with a background of animal data upon which therapeutic interventions for the prevention and treatment of cerebral palsy, benefit this community, and increasingly do so in the future.

Aged garlic extract restores nitric oxide bioavailability in cultured human endothelial cells even under conditions of homocysteine elevation

ETHNOPHARMACOLOGICAL RELEVANCE

Supplementation with aged garlic extract (AGE) has been shown to restore impaired endothelium-dependent vasodilator response in subjects with acutely elevated plasma homocysteine (Hcy) levels after an oral methionine load and in patients with chronic coronary artery disease. Moreover, AGE has been shown to inhibit the progression of coronary calcifications in patients with coronary artery disease. The molecular mechanisms, by which AGE preserves endothelial function is unknown. Our objective was to explore whether AGE preserves endothelial nitric oxide (NO) output even under conditions of elevated Hcy levels by preventing oxidative inactivation of the NO synthase cofactor tetrahydrobiopterin.

MATERIAL AND METHODS

Endothelial (EA.hy 926) cells were incubated with hypoxanthine, aminopterin, thymidine and methionine (HAT/MET) to increase cellular Hcy levels, and with and without AGE. Agonist stimulated NO output was measured using the fluorescent probe DAF-2, and cellular thiol levels (Hcy, cysteine, reduced and oxidized glutathione) and cellular tetrahydrobiopterin levels were measured by high performance liquid chromatography.

RESULTS

HAT/MET incubation resulted in significantly increased cellular Hcy levels, unaffected by coincubation with AGE. Elevated Hcy went along with significantly decreased NO output (to 34.4 ± 4.4% of control) and levels of tetrahydrobiopterin (from 4.67 ± 2.17 to 2.17 ± 0.97 pmol/mg). Incubation with AGE (5mg/mL) in HAT/MET-treated cells prevented the declines in NO output and tetrahydrobiopterin levels. AGE increased cellular levels of cysteine and total glutathione, and prevented glutathione and tetrahydrobiopterin oxidation induced by elevated Hcy.

CONCLUSION

Incubation with AGE preserved normal NO output from endothelial cells even under conditions of elevated Hcy levels by increasing cellular thiol antioxidant and prevention of tetrahydrobiopterin oxidation. This suggests that AGE might be useful in the prevention of endothelial dysfunction.

Activation of cGMP/protein kinase G pathway in postconditioned myocardium depends on reduced oxidative stress and preserved endothelial nitric oxide synthase coupling

BACKGROUND

The cGMP/protein kinase G (PKG) pathway is involved in the cardioprotective effects of postconditioning (PoCo). Although PKG signaling in PoCo has been proposed to depend on the activation of the phosphatidylinositol 3-kinase (PI3K)/Akt cascade, recent data bring into question a causal role of reperfusion injury signaling kinase (RISK) in PoCo protection. We hypothesized that PoCo increases PKG activity by reducing oxidative stress-induced endothelial nitric oxide synthase (NOS) uncoupling at the onset of reperfusion.

METHODS AND RESULTS

Isolated rat hearts were submitted to 40 minutes of ischemia and reperfusion with and without a PoCo protocol. PoCo reduced infarct size by 48% and cGMP depletion. Blockade of cGMP synthesis (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) and inhibition of PKG (KT5823) or NOS (l-NAME) abolished protection, but inhibition of PI3K/Akt cascade (LY294002) did not (n=5 to 7 per group). Phosphorylation of the RISK pathway was higher in PoCo hearts. However, this difference is due to increased cell death in control hearts because in hearts reperfused with the contractile inhibitor blebbistatin, a drug effective in preventing cell death at the onset of reperfusion, RISK phosphorylation increased during reperfusion without differences between control and PoCo groups. In these hearts, PoCo reduced the production of superoxide (O2(-)) and protein nitrotyrosylation and increased nitrate/nitrite levels in parallel with a significant decrease in the oxidation of tetrahydrobiopterin (BH4) and in the monomeric form of endothelial NOS.

CONCLUSIONS

These results demonstrate that PoCo activates the cGMP/PKG pathway via a mechanism independent of the PI3K/Akt cascade and dependent on the reduction of O2(-) production at the onset of reperfusion, resulting in attenuated oxidation of BH4 and reduced NOS uncoupling.

Impact of SOD in eNOS uncoupling: a two-edged sword between hydrogen peroxide and peroxynitrite

In endothelial cell dysfunction, the uncoupling of eNOS results in higher superoxide (O(2)(•-)) and lower NO production and a reduction in NO availability. Superoxide reacts with NO to form a potent oxidizing agent peroxynitrite (ONOO(-)) resulting in nitrosative and nitroxidative stresses and dismutates to form hydrogen peroxide. Studies have shown superoxide dismutase (SOD) plays an important role in reduction of O(2)(•-) and ONOO(-) during eNOS uncoupling. However, the administration or over-expression of SOD was ineffective or displayed deleterious effects in some cases. An understanding of interactions of the two enzyme systems eNOS and SOD is important in determining endothelial cell function. We analyzed complex biochemical interactions involving eNOS and SOD in eNOS uncoupling. A computational model of biochemical pathway of the eNOS-related NO and O(2)(•-) production and downstream reactions involving NO, O(2)(•-), ONOO(-), H(2)O(2) and SOD was developed. The effects of SOD concentration on the concentration profiles of NO, O(2)(•-), ONOO(-) and H(2)O(2) in eNOS coupling/uncoupling were investigated. The results include (i) SOD moderately improves NO production and concentration during eNOS uncoupling, (ii) O(2)(•-) production rate is independent of SOD concentration, (iii) Increase in SOD concentration from 0.1 to 100 μM reduces O(2)(•-) concentration by 90% at all [BH(4)]/[TBP] ratios, (iv) SOD reduces ONOO(-) concentration and increases H(2)O(2) concentration during eNOS uncoupling, (v) Catalase can reduce H(2)O(2) concentration and (vi) Dismutation rate by SOD is the most sensitive parameter during eNOS uncoupling. Thus, SOD plays a dual role in eNOS uncoupling as an attenuator of nitrosative/nitroxidative stress and an augmenter of oxidative stress.

Tetrahydrobiopterin protects soluble guanylate cyclase against oxidative inactivation

Tetrahydrobiopterin (BH4) is a major endogenous vasoprotective agent that improves endothelial function by increasing nitric oxide (NO) synthesis and scavenging of superoxide and peroxynitrite. Therefore, administration of BH4 is considered a promising therapy for cardiovascular diseases associated with endothelial dysfunction and oxidative stress. Here we report on a novel function of BH4 that might contribute to the beneficial vascular effects of the pteridine. Treatment of cultured porcine aortic endothelial cells with nitroglycerin (GTN) or 1H-[1,2,4]-oxadiazolo[4,3-a]quinoxaline-1-one (ODQ) resulted in heme oxidation of soluble guanylate cyclase (sGC), as evident from diminished NO-induced cGMP accumulation that was paralleled by increased cGMP response to a heme- and NO-independent activator of soluble guanylate cyclase [4-([(4-carboxybutyl)[2-(5-fluoro-2-([4'-(trifluoromethyl)biphenyl-4-yl]methoxy)phenyl)ethyl]amino]methyl)benzoic acid (BAY 60-2770)]. Whereas scavenging of superoxide and/or peroxynitrite with superoxide dismutase, tiron, Mn(III)tetrakis(4-benzoic acid)porphyrin, and urate had no protective effects, supplementation of the cells with BH4, either by application of BH4 directly or of its precursors dihydrobiopterin or sepiapterin, completely prevented the inhibition of NO-induced cGMP accumulation by GTN and ODQ. Tetrahydroneopterin had the same effect, and virtually identical results were obtained with RFL-6 fibroblasts, suggesting that our observation reflects a general feature of tetrahydropteridines that is unrelated to NO synthase function and not limited to endothelial cells. Protection of sGC against oxidative inactivation may contribute to the known beneficial effects of BH4 in cardiovascular disorders associated with oxidative stress.

Uncoupling of eNOS causes superoxide anion production and impairs NO signaling in the cerebral microvessels of hph-1 mice

In this study, we used the GTP cyclohydrolase I-deficient mice, i.e., hyperphenylalaninemic (hph-1) mice, to test the hypothesis that the loss of tetrahydrobiopterin (BH(4)) in cerebral microvessels causes endothelial nitric oxide synthase (eNOS) uncoupling, resulting in increased superoxide anion production and inhibition of endothelial nitric oxide signaling. Both homozygous mutant (hph-1(-/-)) and heterozygous mutant (hph-1(+/-) mice) demonstrated reduction in GTP cyclohydrolase I activity and reduced bioavailability of BH(4). In the cerebral microvessels of hph-1(+/-) and hph-1(-/-) mice, increased superoxide anion production was inhibited by supplementation of BH(4) or NOS inhibitor- L- N(G) -nitro arginine-methyl ester, indicative of eNOS uncoupling. Expression of 3-nitrotyrosine was significantly increased, whereas NO production and cGMP levels were significantly reduced. Expressions of antioxidant enzymes namely copper and zinc superoxide dismutase, manganese superoxide dismutase, and catalase were not affected by uncoupling of eNOS. Reduced levels of BH(4), increased superoxide anion production, as well as inhibition of NO signaling were not different between the microvessels of male and female mice. The results of our study are the first to demonstrate that, regardless of gender, reduced BH(4) bioavailability causes eNOS uncoupling, increases superoxide anion production, inhibits eNOS/cGMP signaling, and imposes significant oxidative stress in the cerebral microvasculature.

Interference in mevalonate pathway ameliorates homocysteine-induced endothelium-dysfunction

Homocysteine is a risk factor for atherosclerosis and hypertension and induces endothelium-dysfunction. Accumulation of cholesterol and reactive oxygen species plays a key role in the endothelium-dysfunction. This study investigated the hypothesis of an involvement of mevalonate pathway and oxidative pathway in homocysteine-induced endothelial damage. Homocysteine induced impairment of the endothelium-dependent vasorelaxation of rat aortic rings by isometric tension, while it also reduced the nitric oxide level and the nitric oxide synthase activity in human umbilical vein endothelial cells, followed by accumulation of superoxide anion and cholesterol. However, the level of asymmetric dimethylarginine remained unaffected by homocysteine. The adverse effect of homocysteine on endothelial function was found to be partially enhanced either by squalestatin-reducing cholesterol or by superoxide dismutase-reducing superoxide anion. Moreover, this effect of homocysteine could be completely ameliorated by simvastatin, very similar to that of cotreatment of squalestatin and superoxide dismutase. Respectively, mevalonolactone partly or squalene fully attenuated the effect of simvastatin or squalestatin on homocysteine-induced endothelial dysfunction. In conclusion, our results suggested that the mevalonate pathway mediates homocysteine-induced endothelium dysfunction besides the oxidative pathway. Interference in the mevalonate pathway and oxidative pathway provides effective protection of endothelial function.

Tetrahydrobiopterin is functionally distinguishable from tetrahydrodictyopterin in Dictyostelium discoideum Ax2

Dictyostelium discoideum Ax2 produces both L-erythro-tetrahydrobiopterin (BH4) and its stereoisomer D-threo-BH4 (DH4). The putative cofactor function of them for phenylalanine hydroxylase (PAH) was investigated through genetic manipulation and quantitative determination of pteridines. In addition to establishing that dihydropteridine reductase (DHPR) and dihydrofolate reductase (DHFR) constitute the regeneration pathway of both BH4 and DH4, the results suggested that BH4 is a preferential cofactor for PAH in vivo, not a secondary product of DH4, which functions mainly as an antioxidant. Our result also demonstrated that PAH may be essential for Dictyostelium growth in nature, and thus it appears that the organism has evolved a strategy to maintain BH4 level via regeneration pathway at the expense of DH4 under oxidative stress conditions.

Bi-modal dose-dependent cardiac response to tetrahydrobiopterin in pressure-overload induced hypertrophy and heart failure

The exogenous administration of tetrahydrobiopterin (BH4), an essential cofactor of nitric oxide synthase (NOS), has been shown to reduce left ventricular hypertrophy, fibrosis, and cardiac dysfunction in mice with pre-established heart disease induced by pressure-overload. In this setting, BH4 re-coupled endothelial NOS (eNOS), with subsequent reduction of NOS-dependent oxidative stress and reversal of maladaptive remodeling. However, recent studies suggest the effective BH4 dosing may be narrower than previously thought, potentially due to its oxidation upon oral consumption. Accordingly, we assessed the dose response of daily oral synthetic sapropterin dihydrochloride (6-R-l-erythro-5,6,7,8-tetrahydrobiopterin, 6R-BH4) on pre-established pressure-overload cardiac disease. Mice (n=64) were administered 0-400mg/kg/d BH4 by ingesting small pre-made pellets (consumed over 15-30 min). In a dose range of 36-200mg/kg/d, 6R-BH4 suppressed cardiac chamber remodeling, hypertrophy, fibrosis, and oxidative stress with pressure-overload. However, at both lower and higher doses, BH4 had less or no ameliorative effects. The effective doses correlated with a higher myocardial BH4/BH2 ratio. However, BH2 rose linearly with dose, and at the 400mg/kg/d, this lowered the BH4/BH2 ratio back toward control. These results expose a potential limitation for the clinical use of BH4, as variability of cellular redox and perhaps heart disease could produce a variable therapeutic window among individuals. This article is part of a special issue entitled ''Key Signaling Molecules in Hypertrophy and Heart Failure.''