Tetrahydrobiopterin and nitric oxide: mechanistic and pharmacological aspects

Relative Oral Bioavailability and Food Effects of Two Sepiapterin Formulations in Healthy Participants

Sepiapterin is an orally administered drug in development for the treatment of phenylketonuria, an inborn error of metabolism characterized by the deficiency of the phenylalanine-metabolizing enzyme phenylalanine hydroxylase. This study characterized the pharmacokinetics, safety, and tolerability of 2 clinical sepiapterin formulations (Phase 1/2, Phase 3) and the effects of food on the pharmacokinetics of the Phase 3 formulation in healthy participants. In Part A, 18 participants were randomized to one of 2 treatment sequences, each with 4 dosing periods comprising a single dose (20 or 60 mg/kg) of the Phase 1/2 or the Phase 3 formulation with a low-fat diet. In Part B, 14 participants were randomized to one of 2 sequences, each comprising 4 dosing periods of a single dose (20 or 60 mg/kg) of the Phase 3 formulation under fed (high-fat) or fasted conditions. Following oral administration, sepiapterin was quickly absorbed and rapidly and extensively converted to tetrahydrobiopterin (BH4). BH4 was the major circulating active moiety. Under low-fat conditions, the Phase 3 formulation was bioequivalent to the Phase 1/2 formulation at 20 mg/kg, while slightly lower BH4 exposure (approximately 0.81×) for the Phase 3 formulation was observed at 60 mg/kg. BH4 exposure increased to approximately 1.7× under the low-fat condition and approximately 2.8× under the high-fat condition at a dose of either 20 or 60 mg/kg for the Phase 3 formulation, compared with the fasted condition. Both sepiapterin formulations were well tolerated, with no serious or severe adverse events reported. All treatment-emergent adverse events were mild or moderate in severity.

Nitric Oxide: Physiological Functions, Delivery, and Biomedical Applications

Nitric oxide (NO) is a gaseous molecule that has a central role in signaling pathways involved in numerous physiological processes (e.g., vasodilation, neurotransmission, inflammation, apoptosis, and tumor growth). Due to its gaseous form, NO has a short half-life, and its physiology role is concentration dependent, often restricting its function to a target site. Providing NO from an external source is beneficial in promoting cellular functions and treatment of different pathological conditions. Hence, the multifaceted role of NO in physiology and pathology has garnered massive interest in developing strategies to deliver exogenous NO for the treatment of various regenerative and biomedical complexities. NO-releasing platforms or donors capable of delivering NO in a controlled and sustained manner to target tissues or organs have advanced in the past few decades. This review article discusses in detail the generation of NO via the enzymatic functions of NO synthase as well as from NO donors and the multiple biological and pathological processes that NO modulates. The methods for incorporating of NO donors into diverse biomaterials including physical, chemical, or supramolecular techniques are summarized. Then, these NO-releasing platforms are highlighted in terms of advancing treatment strategies for various medical problems.

The Role of Oxidative Stress in Acute Ischemic Stroke-Related Thrombosis

Acute ischemic stroke is a serious life-threatening disease that affects almost 600 million people each year throughout the world with a mortality of more than 10%, while two-thirds of survivors remain disabled. However, the available treatments for ischemic stroke are still limited to thrombolysis and/or mechanical thrombectomy, and there is an urgent need for developing new therapeutic target. Recently, intravascular oxidative stress, derived from endothelial cells, platelets, and leukocytes, has been found to be tightly associated with stroke-related thrombosis. It not only promotes primary thrombus formation by damaging endothelial cells and platelets but also affects thrombus maturation and stability by modifying fibrin components. Thus, oxidative stress is expected to be a novel target for the prevention and treatment of ischemic stroke. In this review, we first discuss the mechanisms by which oxidative stress promotes stroke-related thrombosis, then summarize the oxidative stress biomarkers of stroke-related thrombosis, and finally put forward an antithrombotic therapy targeting oxidative stress in ischemic stroke.

S-nitrosylation of CSF1 receptor increases the efficacy of CSF1R blockage against prostate cancer

Sustained oxidative stress in castration-resistant prostate cancer (CRPC) cells potentiates the overall tumor microenvironment (TME). Targeting the TME using colony-stimulating factor 1 receptor (CSF1R) inhibition is a promising therapy for CRPC. However, the therapeutic response to sustained CSF1R inhibition (CSF1Ri) is limited as a monotherapy. We hypothesized that one of the underlying causes for the reduced efficacy of CSF1Ri and increased oxidation in CRPC is the upregulation and uncoupling of endothelial nitric oxide synthase (NOS3). Here we show that in high-grade PCa human specimens, NOS3 abundance positively correlates with CSF1-CSF1R signaling and remains uncoupled. The uncoupling diminishes NOS3 generation of sufficient nitric oxide (NO) required for S-nitrosylation of CSF1R at specific cysteine sites (Cys 224, Cys 278, and Cys 830). Exogenous S-nitrosothiol administration (with S-nitrosoglutathione (GSNO)) induces S-nitrosylation of CSF1R and rescues the excess oxidation in tumor regions, in turn suppressing the tumor-promoting cytokines which are ineffectively suppressed by CSF1R blockade. Together these results suggest that NO administration could act as an effective combinatorial partner with CSF1R blockade against CRPC. In this context, we further show that exogenous NO treatment with GSNOR successfully augments the anti-tumor ability of CSF1Ri to effectively reduce the overall tumor burden, decreases the intratumoral percentage of anti-inflammatory macrophages, myeloid-derived progenitor cells and increases the percentage of pro-inflammatory macrophages, cytotoxic T lymphocytes, and effector T cells, respectively. Together, these findings support the concept that the NO-CSF1Ri combination has the potential to act as a therapeutic agent that restores control over TME, which in turn could improve the outcomes of PCa patients.

Die Etablierung eines neuen Forschungskonzepts an einem universitären Standort

Neben der klinischen Tätigkeit haben an einem universitären Standort Forschung und Lehre einen großen Stellenwert. Durch die Etablierung eines neuen Forschungslabors an der Universitätsklinik für Gefäßchirurgie der Medizinischen Universität Innsbruck wurden die infrastrukturellen Voraussetzungen zur Gestaltung eines neuen Forschungsschwerpunkts geschaffen. Die Kooperation mit nationalen und internationalen Partnern war für diesen Prozess essenziell. Nicht nur in der Planung und Ausstattung der Räumlichkeiten, sondern auch in der Entwicklung von Studienprotokollen und zur kritischen Diskussion von Ergebnissen ist der Aufbau eines Netzwerkes von großer Bedeutung. Durch die Etablierung der experimentellen Gefäßchirurgie Innsbruck ist nun die Realisierung von Projekten der Grundlagenforschung und der translationalen Forschung an diesem universitären Standort möglich. Zudem spielt die Lehrforschung eine immer größere Rolle, insbesondere um die Ausbildungsstruktur möglichst praxisnah zu gestalten, Nachwuchs anzuwerben und die immer komplexer werdenden Techniken auch praxisnah zu vermitteln.

Selanzylimidazopyridine abolishes inflammation- and stress-induced depressive-like behaviors and decreases oxidonitrosative stress in the prefrontal cortex and hippocampus of mice

The 3-[(4-methoxyphenyl)selanyl]-2-phenylimidazo[1,2-a] pyridine (MPI), a novel organic selenium compound, has been receiving increased attention due to its antioxidant effects and its ability to protect against depression-like behaviours. However, it remains elusive whether MPI is able to reverse depressive-like symptoms and biochemical alterations in mice. In the present work, we explored the ability of MPI (10 mg/kg, i.g.) to reverse inflammation- and stress-induced depression-like behaviours in mice injected with tumour necrosis factor (TNF-α) or submitted to acute restraint stress. Depression-like behaviours were evaluated by the tail suspension and splash test and the open field test was used to evaluate the locomotor activity of mice. The prefrontal cortex and hippocampus of mice were used for the evaluation of parameters of oxidonitrosative stress. Here, we showed that a single administration of MPI abolished the depressive-like behaviours induced by TNF-α and acute restraint stress without having an effect per se. The oxidative and nitrosative stress presented in mice with depression-like behaviours were also decreased by MPI in the prefrontal cortex and hippocampus. Our findings suggest that MPI presents antidepressant-like activity which is associated with the biochemical regulation of oxidative stress in the prefrontal cortex and hippocampus of mice, arising as a promising strategy for the management of depressive symptoms.

Chronic mercury exposure induces oxidative stress in female rats by endothelial nitric oxide synthase uncoupling and cyclooxygenase-2 activation, without affecting oestrogen receptor function

Mercury has been shown to be a significant health risk factor and is positively associated with cardiovascular diseases. Evidence reveals that men are more likely to develop cardiovascular diseases than women during reproductive age. However, the effects of mercury in females remain poorly investigated, despite the finding that female hormones demonstrate a cardioprotective role. In the present study, we evaluated whether chronic mercury chloride exposure could alter blood pressure and vascular function of the female rat aorta. Ten-week-old female Wistar rats were divided into two groups: control (vehicle) and mercury treated (first dose of 4.6 μg/kg, subsequent daily doses of 0.07 μg/kg), im. Mercury treatment did not modify systolic blood pressure (SBP) but increased vascular reactivity due to the reduction of nitric oxide bioavailability associated with the increase in reactive oxygen species from endothelial nitric oxide synthase (eNOS) uncoupling. Furthermore, increased participation of the cyclooxygenase-2 pathway occurred through an imbalance in thromboxane 2 and prostacyclin 2. However, the oestrogen signalling pathway was not altered in either group. These results demonstrated that chronic exposure to mercury in females induced endothelial dysfunction and, consequently, increased aortic vascular reactivity, causing vascular damage to the female rat aorta and representing a risk of cardiovascular diseases.

Autoxidation and photooxidation of tetrahydrobiopterin: a theoretical study

Pterins are naturally occurring pigments and enzyme cofactors widespread in living organisms. Tetrahydrobiopterin (H4Bip) is a coenzyme of aromatic amino acid hydroxylases, NO-synthases, and alkylglycerol monooxygenases. This coenzyme is prone to oxidation in the presence of molecular oxygen, a so-called autoxidation. The reactions participating in H4Bip autoxidation are well known. However, our study is an attempt to evaluate theoretically the feasibility of reactions participating in autoxidation. To do so, we have calculated the Gibbs free energy of elementary reactions between H4Bip, its derivatives, molecular oxygen, and reactive oxygen species (ROS). In the last few years, we have established the photosensitized oxidation of H4Bip experimentally. Thus, we have also evaluated the feasibility of H4Bip photooxidation reactions, which may occur according to both type-I and type-II photosensitized oxidation. We calculated Fukui indices for H4Bip and found particular atoms in the molecule that interact with nucleophiles (for example, singlet oxygen 1O2) and radicals (in particular, molecular oxygen 3O2). Therefore, we evaluated the probability of H4Bip autoxidation reactions, photooxidation reactions, and the reactivity of particular atoms in H4Bip molecule using the theoretical methods of quantum chemistry.

Tetrahydrobioterin (BH4) Pathway: From Metabolism to Neuropsychiatry

Tetrahydrobipterin (BH4) is a pivotal enzymatic cofactor required for the synthesis of serotonin, dopamine and nitric oxide. BH4 is essential for numerous physiological processes at periphery and central levels, such as vascularization, inflammation, glucose homeostasis, regulation of oxidative stress and neurotransmission. BH4 de novo synthesis involves the sequential activation of three enzymes, the major controlling point being GTP cyclohydrolase I (GCH1). Complementary salvage and recycling pathways ensure that BH4 levels are tightly kept within a physiological range in the body. Even if the way of transport of BH4 and its ability to enter the brain after peripheral administration is still controversial, data showed increased levels in the brain after BH4 treatment. Available evidence shows that GCH1 expression and BH4 synthesis are stimulated by immunological factors, notably pro-inflammatory cytokines. Once produced, BH4 can act as an anti- inflammatory molecule and scavenger of free radicals protecting against oxidative stress. At the same time, BH4 is prone to autoxidation, leading to the release of superoxide radicals contributing to inflammatory processes, and to the production of BH2, an inactive form of BH4, reducing its bioavailability. Alterations in BH4 levels have been documented in many pathological situations, including Alzheimer's disease, Parkinson's disease and depression, in which increased oxidative stress, inflammation and alterations in monoaminergic function are described. This review aims at providing an update of the knowledge about metabolism and the role of BH4 in brain function, from preclinical to clinical studies, addressing some therapeutic implications.

Synthetic Fe/Cu Complexes: Toward Understanding Heme-Copper Oxidase Structure and Function

Heme-copper oxidases (HCOs) are terminal enzymes on the mitochondrial or bacterial respiratory electron transport chain, which utilize a unique heterobinuclear active site to catalyze the 4H+/4e- reduction of dioxygen to water. This process involves a proton-coupled electron transfer (PCET) from a tyrosine (phenolic) residue and additional redox events coupled to transmembrane proton pumping and ATP synthesis. Given that HCOs are large, complex, membrane-bound enzymes, bioinspired synthetic model chemistry is a promising approach to better understand heme-Cu-mediated dioxygen reduction, including the details of proton and electron movements. This review encompasses important aspects of heme-O2 and copper-O2 (bio)chemistries as they relate to the design and interpretation of small molecule model systems and provides perspectives from fundamental coordination chemistry, which can be applied to the understanding of HCO activity. We focus on recent advancements from studies of heme-Cu models, evaluating experimental and computational results, which highlight important fundamental structure-function relationships. Finally, we provide an outlook for future potential contributions from synthetic inorganic chemistry and discuss their implications with relevance to biological O2-reduction.

Brain Kynurenine and BH4 Pathways: Relevance to the Pathophysiology and Treatment of Inflammation-Driven Depressive Symptoms

The prevalence of depressive disorders is growing worldwide, notably due to stagnation in the development of drugs with greater antidepressant efficacy, the continuous large proportion of patients who do not respond to conventional antidepressants, and the increasing rate of chronic medical conditions associated with an increased vulnerability to depressive comorbidities. Accordingly, better knowledge on the pathophysiology of depression and mechanisms underlying depressive comorbidities in chronic medical conditions appears urgently needed, in order to help in the development of targeted therapeutic strategies. In this review, we present evidence pointing to inflammatory processes as key players in the pathophysiology and treatment of depressive symptoms. In particular, we report preclinical and clinical findings showing that inflammation-driven alterations in specific metabolic pathways, namely kynurenine and tetrahydrobiopterin (BH4) pathways, leads to substantial alterations in the metabolism of serotonin, glutamate and dopamine that are likely to contribute to the development of key depressive symptom dimensions. Accordingly, anti-inflammatory interventions targeting kynurenine and BH4 pathways may be effective as novel treatment or as adjuvants of conventional medications rather directed to monoamines, notably when depressive symptomatology and inflammation are comorbid in treated patients. This notion is discussed in the light of recent findings illustrating the tight interactions between known antidepressant drugs and inflammatory processes, as well as their therapeutic implications. Altogether, this review provides valuable findings for moving toward more adapted and personalized therapeutic strategies to treat inflammation-related depressive symptoms.

Nitrate, the oral microbiome, and cardiovascular health: a systematic literature review of human and animal studies

Background

Dietary nitrate is an important source of nitric oxide (NO), a molecule critical for cardiovascular health. Nitrate is sequentially reduced to NO through an enterosalivary nitrate-nitrite-NO pathway that involves the oral microbiome. This pathway is considered an important adjunct pathway to the classical l-arginine-NO synthase pathway.

Objective

The objective of this study was to systematically assess the evidence for dietary nitrate intake and improved cardiovascular health from both human and animal studies.

Design

A systematic literature search was performed according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines by using key search terms in Medline and EMBASE databases and defined inclusion and exclusion criteria.

Results

Thirty-seven articles on humans and 14 articles on animals were included from 12,541 screened references. Data on the effects of dietary nitrate on blood pressure, endothelial function, ischemic reperfusion injury, arterial stiffness, platelet function, and cerebral blood flow in both human and animal models were identified. Beneficial effects of nitrate on vascular health have predominantly been observed in healthy human populations, whereas effects in populations at risk of cardiovascular disease are less clear. Few studies have investigated the long-term effects of dietary nitrate on cardiovascular disease clinical endpoints. In animal studies, there is evidence that nitrate improves blood pressure and endothelial function, particularly in animal models with reduced NO bioavailability. Nitrate dose seems to be a critical factor because there is evidence of cross-talk between the 2 pathways of NO production.

Conclusions

Evidence for a beneficial effect in humans at risk of cardiovascular disease is limited. Furthermore, there is a need to investigate the long-term effects of dietary nitrate on cardiovascular disease clinical endpoints. Further animal studies are required to elucidate the mechanisms behind the observed effects.

Low-density lipoprotein modified by myeloperoxidase oxidants induces endothelial dysfunction

Low-density lipoprotein (LDL) modified by hypochlorous acid (HOCl) produced by myeloperoxidase (MPO) is present in atherosclerotic lesions, where it is implicated in the propagation of inflammation and acceleration of lesion development by multiple pathways, including the induction of endothelial dysfunction. Thiocyanate (SCN^-) ions are utilised by MPO to produce the oxidant hypothiocyanous acid (HOSCN), which reacts with LDL in a different manner to HOCl. Whilst the reactivity of HOCl-modified LDL has been previously studied, the role of HOSCN in the modification of LDL in vivo is poorly defined, although emerging evidence suggests that these particles have distinct biological properties. This is important because elevated plasma SCN^- is linked with both the propagation and prevention of atherosclerosis. In this study, we demonstrate that both HOSCN- and HOCl-modified LDL inhibit endothelium-mediated vasorelaxation ex vivo in rat aortic ring segments. In vitro experiments with human coronary artery endothelial cells show that HOSCN-modified LDL decreases in the production of nitric oxide (NO^•) and induces the loss of endothelial nitric oxide synthase (eNOS) activity. This occurs to a similar extent to that seen with HOCl-modified LDL. In each case, these effects are related to eNOS uncoupling, rather than altered expression, phosphorylation or cellular localisation. Together, these data provide new insights into role of MPO and LDL modification in the induction of endothelial dysfunction, which has implications for both the therapeutic use of SCN^- within the setting of atherosclerosis and for smokers, who have elevated plasma levels of SCN^-, and are more at risk of developing cardiovascular disease.

•

Myeloperoxidase produces HOCl and HOSCN that modify LDL in a distinct manner.

•

HOSCN- and HOCl-LDL inhibit endothelium-mediated vasorelaxation in aortic rings ex vivo.

•

HOSCN- and HOCl-LDL decrease endothelial production of nitric oxide in vitro.

•

Decreased eNOS activity is seen, which associated with enzyme uncoupling.

•

HOSCN- and HOCl-LDL induce colocalisation of eNOS and caveolin 1.

Tetrahydrobiopterin improves microcirculation in experimental sepsis

BACKGROUND

Tetrahydrobiopterin (BH4), an endogenous nucleic acid derivative, acts as an important cofactor for several enzymes found within the vascular endothelium, which is deranged in sepsis.

OBJECTIVE

We hypothesized that BH4 would improve capillary density and decrease inflammation within the intestinal microcirculation of septic rats.

METHODS

We conducted a randomized, controlled trial using two previously validated models of sepsis in rats: 1) A fecal peritonitis model using a stent perforating the ascending colon, and 2) An endotoxemia model using lipopolysaccharide (LPS) toxin from E. coli. Experimental groups receiving BH4 (60 mg/kg) were compared to otherwise healthy controls and to untreated groups with sepsis-like physiology.

RESULTS

BH4 decreased leukocyte-endothelial adhesion by 55% and 58% (P < 0.05) in the peritonitis model and endotoxemia models, respectively. In the endotoxemia model but not the peritonitis model, BH4 improved functional capillary density in capillary beds within the intestine (141.3 vs. 106.7 mm/cm2, p < 0.05). Macrohemodynamic parameters were no different between placebo treatment and BH4-treated groups.

CONCLUSIONS

This study demonstrates that BH4 improves capillary density and inflammation in two separate models of sepsis. BH4 may represent a novel adjunct in the treatment of sepsis and septic shock in clinical practice. Further dose-finding studies and clinical trials are warranted.

Disturbed Serotonergic Neurotransmission and Oxidative Stress in Elderly Patients with Delirium

Background

Oxidative stress and disturbances in serotonergic and dopaminergic neurotransmission may play a role in the pathophysiology of delirium.

Aims

In this study, we investigated levels of amino acids, amino acid ratios and levels of homovanillic acid (HVA) as indicators for oxidative stress and disturbances in neurotransmission.

Methods

Plasma levels of amino acids, amino acid ratios and HVA were determined in acutely ill patients aged ≥65 years admitted to the wards of Internal Medicine and Geriatrics of the Erasmus University Medical Center and the ward of Geriatrics of the Havenziekenhuis, Rotterdam, The Netherlands. Differences in the biochemical parameters between patients with and without delirium were investigated by analysis of variance in models adjusted for age, gender and comorbidities.

Results

Of the 86 patients included, 23 had delirium. In adjusted models, higher mean phenylalanine/tyrosine ratios (1.34 vs. 1.14, p = 0.028), lower mean tryptophan/large neutral amino acids ratios (4.90 vs. 6.12, p = 0.021) and lower mean arginine levels (34.8 vs. 45.2 µmol/l, p = 0.022) were found in patients with delirium when compared to those without. No differences were found in HVA levels between patients with and without delirium.

Conclusion

The findings of this study suggest disturbed serotonergic neurotransmission and an increased status of oxidative stress in patients with delirium.

Vascular nitric oxide: Beyond eNOS

As the first discovered gaseous signaling molecule, nitric oxide (NO) affects a number of cellular processes, including those involving vascular cells. This brief review summarizes the contribution of NO to the regulation of vascular tone and its sources in the blood vessel wall. NO regulates the degree of contraction of vascular smooth muscle cells mainly by stimulating soluble guanylyl cyclase (sGC) to produce cyclic guanosine monophosphate (cGMP), although cGMP-independent signaling [S-nitrosylation of target proteins, activation of sarco/endoplasmic reticulum calcium ATPase (SERCA) or production of cyclic inosine monophosphate (cIMP)] also can be involved. In the blood vessel wall, NO is produced mainly from l-arginine by the enzyme endothelial nitric oxide synthase (eNOS) but it can also be released non-enzymatically from S-nitrosothiols or from nitrate/nitrite. Dysfunction in the production and/or the bioavailability of NO characterizes endothelial dysfunction, which is associated with cardiovascular diseases such as hypertension and atherosclerosis.

Uncoupling of endothelial nitric oxide synthase in cerebral vasculature of Tg2576 mice

In this study, we tested the hypothesis that reduced bioavailability of tetrahydrobiopterin (BH4) is a major mechanism responsible for pathogenesis of endothelial dysfunction in cerebral microvessels of transgenic mice expressing the Swedish double mutation of human amyloid precursor protein (APP) (Tg2576 mice). Endothelial nitric oxide synthase (eNOS) protein expression was significantly increased in cerebral vasculature of Tg2576 mice. In contrast, bioavailability of BH4 was significantly reduced (p < 0.05). Moreover, superoxide anion production was increased in cerebral microvessels of Tg2576 mice (p < 0.05). Incubation with NOS inhibitor, Nω-nitro-L-arginine methyl ester, decreased superoxide anion indicating that uncoupled eNOS is most likely the source of superoxide anion. Increasing BH4 bioavailability either exogenously by BH4 supplementation or endogenously by treatment with the selective peroxisome proliferator-activated receptor--delta activator GW501516 (2 mg/kg/day, 14 days) attenuated eNOS uncoupling and decreased superoxide anion production in cerebral microvessels of Tg2576 mice (p < 0.05). Treatment with GW501516 restored the biological activity of endothelial nitric oxide in cerebral microvessels of Tg2576 mice, as indicated by the increased nitrite/nitrate content and 3,5-cyclic guanosine monophosphate levels (p < 0.05). Our studies indicate that sub-optimal BH4 bioavailability in cerebral vasculature is an important contributor to oxidant stress and endothelial dysfunction in Tg2576 mouse model of Alzheimer's disease. Existing evidence suggests that Aβ peptides-induced up-regulation of expression and activity of NADPH oxidase causes increased production of superoxide anion (.O2(-)). .O2(-) can also be converted to hydrogen peroxide (H2O2) by enzymatic activity of superoxide dismutase (SOD) or spontaneous dismutation. Elevation of .O2(-) and H2O2 might cause oxidation of tetrahydrobiopterin (BH4) to dihydrobiopterin (BH2) and subsequent uncoupling of endothelial nitric oxide synthase (eNOS) (a) thus reducing levels of nitric oxide (NO) and 3',5'-cyclic guanosine monophosphate (cGMP). Supplementation of BH4 or activation of PPARδ prevents detrimental effects of eNOS uncoupling by restoring bioavailability of BH4 and scavenging of .O2(-), respectively (b). Activation of PPARδ also increases expression of catalase thereby inactivating H2O2. Generation of H2O2 by uncoupled eNOS in cerebral microvessels of Tg2576 mice is hypothetical.

l -Citrulline, But Not l -Arginine, Prevents Diabetes Mellitus–Induced Glomerular Hyperfiltration and Proteinuria in Rat

Diabetes mellitus–induced oxidative stress causes increased renal oxygen consumption and intrarenal tissue hypoxia. Nitric oxide is an important determinant of renal oxygen consumption and electrolyte transport efficiency. The present study investigates whether l -arginine or l -citrulline to promote nitric oxide production prevents the diabetes mellitus–induced kidney dysfunction. Glomerular filtration rate, renal blood flow, in vivo oxygen consumption, tissue oxygen tension, and proteinuria were investigated in control and streptozotocin-diabetic rats with and without chronic l -arginine or l -citrulline treatment for 3 weeks. Untreated and l -arginine–treated diabetic rats displayed increased glomerular filtration rate (2600±162 versus 1599±127 and 2290±171 versus 1739±138 µL/min per kidney), whereas l -citrulline prevented the increase (1227±126 versus 1375±88 µL/min per kidney). Filtration fraction was increased in untreated diabetic rats because of the increase in glomerular filtration rate but not in l -arginine– or l -citrulline–treated diabetic rats. Urinary protein excretion was increased in untreated and l -arginine–treated diabetic rats (142±25 versus 75±7 and 128±7 versus 89±7 µg/min per kidney) but not in diabetic rats administered l -citrulline (67±7 versus 61±5 µg/min per kidney). The diabetes mellitus–induced tissue hypoxia, because of elevated oxygen consumption, was unaltered by any of the treatments. l -citrulline administered to diabetic rats increases plasma l -arginine concentration, which prevents the diabetes mellitus–induced glomerular hyperfiltration, filtration fraction, and proteinuria, possibly by a vascular effect.

Interaction between neuronal nitric-oxide synthase and tetrahydrobiopterin revisited: studies on the nature and mechanism of tight pterin binding

Recombinant neuronal nitric-oxide synthase (nNOS) expressed in baculovirus-infected Sf9 cells contains approximately 1 equiv of tightly bound tetrahydrobiopterin (BH4) per dimer and binds a second equivalent with a dissociation constant in the 10(-7)-10(-6) M range. Less is known about the pterin-binding properties of nNOS originating from expression systems such as Escherichia coli that do not produce BH4. We determined the binding properties of E. coli-expressed nNOS for BH4 and several inhibitory pterins by monitoring their effects on enzyme activity. E. coli-expressed nNOS as isolated was activated by BH4 monophasically with EC50 ≈ 2 × 10(-7) M, demonstrating a lack of tight pterin binding. However, overnight incubation with BH4 resulted in tight binding of one BH4 per dimer, yielding an enzyme that resembled Sf9-expressed nNOS. Tight pterin binding was also induced by preincubation with 4-amino-tetrahydrobiopterin, but not by 7,8-dihydrobiopterin or 4-amino-dihydrobiopterin, suggesting that tight-binding site formation requires preincubation with a fully reduced pteridine. Kinetic experiments showed that tight-binding site formation takes approximately 10 min with 1 μM BH4 (2 min with 1 μM 4-amino-BH4) at 4 °C. Anaerobic preincubation experiments demonstrated that O2 is not involved in the process. Gel electrophoretic studies suggest that tight-binding site formation is accompanied by an increase in the strength of the NOS dimer. We propose that incubation of pterin-free nNOS with BH4 creates one tight pterin-binding site per dimer, leaving the other site unaffected, in a reaction that involves redox chemistry.

The complex interplay of iron metabolism, reactive oxygen species, and reactive nitrogen species: insights into the potential of various iron therapies to induce oxidative and nitrosative stress

Production of minute concentrations of superoxide (O2(*-)) and nitrogen monoxide (nitric oxide, NO*) plays important roles in several aspects of cellular signaling and metabolic regulation. However, in an inflammatory environment, the concentrations of these radicals can drastically increase and the antioxidant defenses may become overwhelmed. Thus, biological damage may occur owing to redox imbalance-a condition called oxidative and/or nitrosative stress. A complex interplay exists between iron metabolism, O2(*-), hydrogen peroxide (H2O2), and NO*. Iron is involved in both the formation and the scavenging of these species. Iron deficiency (anemia) (ID(A)) is associated with oxidative stress, but its role in the induction of nitrosative stress is largely unclear. Moreover, oral as well as intravenous (iv) iron preparations used for the treatment of ID(A) may also induce oxidative and/or nitrosative stress. Oral administration of ferrous salts may lead to high transferrin saturation levels and, thus, formation of non-transferrin-bound iron, a potentially toxic form of iron with a propensity to induce oxidative stress. One of the factors that determine the likelihood of oxidative and nitrosative stress induced upon administration of an iv iron complex is the amount of labile (or weakly-bound) iron present in the complex. Stable dextran-based iron complexes used for iv therapy, although they contain only negligible amounts of labile iron, can induce oxidative and/or nitrosative stress through so far unknown mechanisms. In this review, after summarizing the main features of iron metabolism and its complex interplay with O2(*-), H2O2, NO*, and other more reactive compounds derived from these species, the potential of various iron therapies to induce oxidative and nitrosative stress is discussed and possible underlying mechanisms are proposed. Understanding the mechanisms, by which various iron formulations may induce oxidative and nitrosative stress, will help us develop better tolerated and more efficient therapies for various dysfunctions of iron metabolism.

Coronary artery spasm related to thiol oxidation and senescence marker protein-30 in aging

BACKGROUND

Senescence marker protein-30 (SMP30) decreases with aging, and SMP30 knockout (KO) mice show a short life with increased oxidant stress.

AIMS

We assessed the effect of oxidant stress with SMP30 deficiency in coronary artery spasm and clarify its underlying mechanisms.

RESULTS

We measured vascular responses to acetylcholine (ACh) and sodium nitroprusside (SNP) of isolated coronary arteries from SMP30 KO and wild-type (WT) mice. In SMP30 KO mice, ACh-induced vasoconstriction occurred, which was changed to vasodilation by dithiothreitol (DTT), a thiol-reducing agent. However, Nω-nitro-L-arginine-methyl ester, nitric oxide (NO) synthase inhibitor, or tetrahydrobiopterin did not change the ACh response. In isolated coronary arteries of WT mice, ACh-induced vasodilation occurred. Inhibition of glutathione reductase by 1, 3-bis(2-chloroethyl)-1-nitrosourea decreased ACh-induced vasodilation (n=10, p<0.01), which was restored by DTT. To evaluate the thiol oxidation, we measured the fluorescence of monochlorobimane (MCB) in coronary arteries, which covalently labels the total. The fluorescence level to MCB decreased in SMP30 KO mice, but with DTT treatment restored to a level comparable to that of WT mice. The reduced glutathione and total thiol levels were also low in the aorta of SMP30 KO mice compared with those of WT mice. Administration of ACh into the aortic sinus in vivo of SMP30 KO mice induced coronary artery spasm.

INNOVATION

The thiol redox state is a key regulator of endothelial NO synthase activity, and thiol oxidation was associated with endothelial dysfunction in the SMP30 deficiency model.

CONCLUSION

These results suggest that chronic thiol oxidation by oxidant stress is a trigger of coronary artery spasm, resulting in impaired endothelium-dependent vasodilation.

Microenvironments in tuberculous granulomas are delineated by distinct populations of macrophage subsets and expression of nitric oxide synthase and arginase isoforms

Macrophages in granulomas are both antimycobacterial effector and host cell for Mycobacterium tuberculosis, yet basic aspects of macrophage diversity and function within the complex structures of granulomas remain poorly understood. To address this, we examined myeloid cell phenotypes and expression of enzymes correlated with host defense in macaque and human granulomas. Macaque granulomas had upregulated inducible and endothelial NO synthase (iNOS and eNOS) and arginase (Arg1 and Arg2) expression and enzyme activity compared with nongranulomatous tissue. Immunohistochemical analysis indicated macrophages adjacent to uninvolved normal tissue were more likely to express CD163, whereas epithelioid macrophages in regions where bacteria reside strongly expressed CD11c, CD68, and HAM56. Calprotectin-positive neutrophils were abundant in regions adjacent to caseum. iNOS, eNOS, Arg1, and Arg2 proteins were identified in macrophages and localized similarly in granulomas across species, with greater eNOS expression and ratio of iNOS/Arg1 expression in epithelioid macrophages as compared with cells in the lymphocyte cuff. iNOS, Arg1, and Arg2 expression in neutrophils was also identified. The combination of phenotypic and functional markers support that macrophages with anti-inflammatory phenotypes localized to outer regions of granulomas, whereas the inner regions were more likely to contain macrophages with proinflammatory, presumably bactericidal, phenotypes. Together, these data support the concept that granulomas have organized microenvironments that balance antimicrobial anti-inflammatory responses to limit pathology in the lungs.

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.

New evidence for assessing tetrahydrobiopterin (BH(4)) responsiveness

OBJECTIVE

To evaluate the protocol we propose for detecting BH(4)-responsive patients and the possibility of delimiting more precisely the population to be tested.

METHODS

We recruited 102 phenylketonuric patients on a phenylalanine (Phe)-restricted diet. The initial stage of the protocol was a 24-h BH(4) loading test involving Phe loading and subsequent ingestion of the cofactor, a 50% fall in blood Phe levels being considered a positive response. The non-responders at this stage then completed a one-week therapeutic test combining BH(4) administration and daily protein intake meeting recommended dietary allowances, to assess whether the 24-h test had detected all responders.

RESULTS

The 24-h test detected almost all BH(4) responders (30.3% of the 99 patients included in the analysis), with just two patients (2.0%) subsequently responding positively to the therapeutic test. The 24-h test did not give any false positive results.

CONCLUSIONS

The 24-h BH(4) loading test is clinically useful for screening phenylketonuric patients. Specifically, 95% of patients with Phe levels <700 μmol/L, and none with Phe levels >1500 μmol/L were BH(4)-responsive. Given these results, we conclude that patients with Phe levels<700 μmol/L or>1500 μmol/L probably do not need to be tested, prioritising the identification of BH(4)-responsiveness among individuals with intermediate Phe concentrations, between the aforementioned values. Additionally, our results suggest that the therapeutic test only needs to be performed in cases where the reduction in blood Phe levels after cofactor administration is within the range 40%-50%.

The Protective Effect of Minocycline in a Paraquat-Induced Parkinson's Disease Model in Drosophila is Modified in Altered Genetic Backgrounds

Epidemiological studies link the herbicide paraquat to increased incidence of Parkinson's disease (PD). We previously reported that Drosophila exposed to paraquat recapitulate PD symptoms, including region-specific degeneration of dopaminergic neurons. Minocycline, a tetracycline derivative, exerts ameliorative effects in neurodegenerative disease models, including Drosophila. We investigated whether our environmental toxin-based PD model could contribute to an understanding of cellular and genetic mechanisms of minocycline action and whether we could assess potential interference with these drug effects in altered genetic backgrounds. Cofeeding of minocycline with paraquat prolonged survival, rescued mobility defects, blocked generation of reactive oxygen species, and extended dopaminergic neuron survival, as has been reported previously for a genetic model of PD in Drosophila. We then extended this study to identify potential interactions of minocycline with genes regulating dopamine homeostasis that might modify protection against paraquat and found that deficits in GTP cyclohydrolase adversely affect minocycline rescue. We further performed genetic studies to identify signaling pathways that are necessary for minocycline protection against paraquat toxicity and found that mutations in the Drosophila genes that encode c-Jun N-terminal kinase (JNK) and Akt/Protein kinase B block minocycline rescue.

Therapeutic effect of enhancing endothelial nitric oxide synthase (eNOS) expression and preventing eNOS uncoupling

Nitric oxide (NO) produced by the endothelium is an important protective molecule in the vasculature. It is generated by the enzyme endothelial NO synthase (eNOS). Similar to all NOS isoforms, functional eNOS transfers electrons from nicotinamide adenine dinucleotide phosphate (NADPH), via the flavins flavin adenine dinucleotide and flavin mononucleotide in the carboxy-terminal reductase domain, to the heme in the amino-terminal oxygenase domain. Here, the substrate L-arginine is oxidized to L-citrulline and NO. Cardiovascular risk factors such as diabetes mellitus, hypertension, hypercholesterolaemia or cigarette smoking reduce bioactive NO. These risk factors lead to an enhanced production of reactive oxygen species (ROS) in the vessel wall. NADPH oxidases represent major sources of this ROS and have been found upregulated in the presence of cardiovascular risk factors. NADPH-oxidase-derived superoxide avidly reacts with eNOS-derived NO to form peroxynitrite (ONOO(-)). The essential NOS cofactor (6R-)5,6,7,8-tetrahydrobiopterin (BH(4) ) is highly sensitive to oxidation by this ONOO(-). In BH(4) deficiency, oxygen reduction uncouples from NO synthesis, thereby converting NOS to a superoxide-producing enzyme. Among conventional drugs, compounds interfering with the renin-angiotensin-aldosterone system and statins can reduce vascular oxidative stress and increase bioactive NO. In recent years, we have identified a number of small molecules that have the potential to prevent eNOS uncoupling and, at the same time, enhance eNOS expression. These include the protein kinase C inhibitor midostaurin, the pentacyclic triterpenoids ursolic acid and betulinic acid, the eNOS enhancing compounds AVE9488 and AVE3085, and the polyphenolic phytoalexin trans-resveratrol. Such compounds enhance NO production from eNOS also under pathophysiological conditions and may thus have therapeutic potential.

Nitric oxide synthases: regulation and function

Nitric oxide (NO), the smallest signalling molecule known, is produced by three isoforms of NO synthase (NOS; EC 1.14.13.39). They all utilize l-arginine and molecular oxygen as substrates and require the cofactors reduced nicotinamide-adenine-dinucleotide phosphate (NADPH), flavin adenine dinucleotide (FAD), flavin mononucleotide (FMN), and (6R-)5,6,7,8-tetrahydrobiopterin (BH(4)). All NOS bind calmodulin and contain haem. Neuronal NOS (nNOS, NOS I) is constitutively expressed in central and peripheral neurons and some other cell types. Its functions include synaptic plasticity in the central nervous system (CNS), central regulation of blood pressure, smooth muscle relaxation, and vasodilatation via peripheral nitrergic nerves. Nitrergic nerves are of particular importance in the relaxation of corpus cavernosum and penile erection. Phosphodiesterase 5 inhibitors (sildenafil, vardenafil, and tadalafil) require at least a residual nNOS activity for their action. Inducible NOS (NOS II) can be expressed in many cell types in response to lipopolysaccharide, cytokines, or other agents. Inducible NOS generates large amounts of NO that have cytostatic effects on parasitic target cells. Inducible NOS contributes to the pathophysiology of inflammatory diseases and septic shock. Endothelial NOS (eNOS, NOS III) is mostly expressed in endothelial cells. It keeps blood vessels dilated, controls blood pressure, and has numerous other vasoprotective and anti-atherosclerotic effects. Many cardiovascular risk factors lead to oxidative stress, eNOS uncoupling, and endothelial dysfunction in the vasculature. Pharmacologically, vascular oxidative stress can be reduced and eNOS functionality restored with renin- and angiotensin-converting enzyme-inhibitors, with angiotensin receptor blockers, and with statins.

Modulated expression of genes associated with NO signal transduction contributes to the cholesterol-lowering effect of electro-acupuncture

Electro-acupuncture (EA) at Fenglong acupoint (ST40) can lower the levels of serum cholesterol and triacylglycerols. To study the hepatic genes responsible for the cholesterol-lowering effect of EA, suppression subtractive hybridization combined with the switch mechanism at the 5'-end of RNA template cDNA synthesis and long-distance PCR were employed using hepatic tissues from hypercholesterolemia and EA-treated mice. 68 % of the identified genes are involved in metabolism, immune response, and signal transduction pathways. Real-time PCR and western blot indicate that EA at ST40 induces the expression of nNOS and Mt1, two genes involved in NO signal transduction. EA treatment for hypercholesterolemia thus involves the modulation of several biological pathways and provides a physiological link between NO signal transduction and the cholesterol-lowering effect of EA.

Oxygen-dependent regulation of nitric oxide production by inducible nitric oxide synthase

Inducible nitric oxide synthase (iNOS) catalyzes the reaction that converts the substrates O(2) and l-arginine to the products nitric oxide (NO) and l-citrulline. Macrophages, and many other cell types, upregulate and express iNOS primarily in response to inflammatory stimuli. Physiological and pathophysiological oxygen tension can regulate NO production by iNOS at multiple levels, including transcriptional, translational, posttranslational, enzyme dimerization, cofactor availability, and substrate dependence. Cell culture techniques that emphasize control of cellular PO(2), and measurement of NO or its stable products, have been used by several investigators for in vitro study of the O(2) dependence of NO production at one or more of these levels. In most cell types, prior or concurrent exposure to cytokines or other inflammatory stimuli is required for the upregulation of iNOS mRNA and protein by hypoxia. Important transcription factors that target the iNOS promoter in hypoxia include hypoxia-inducible factor 1 and/or nuclear factor κB. In contrast to the upregulation of iNOS by hypoxia, in most cell types NO production is reduced by hypoxia. Recent work suggests a prominent role for O(2) substrate dependence in the short-term regulation of iNOS-mediated NO production.

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.

Sepiapterin improves angiogenesis of pulmonary artery endothelial cells with in utero pulmonary hypertension by recoupling endothelial nitric oxide synthase

Persistent pulmonary hypertension of the newborn (PPHN) is associated with decreased blood vessel density that contributes to increased pulmonary vascular resistance. Previous studies showed that uncoupled endothelial nitric oxide (NO) synthase (eNOS) activity and increased NADPH oxidase activity resulted in marked decreases in NO bioavailability and impaired angiogenesis in PPHN. In the present study, we hypothesize that loss of tetrahydrobiopterin (BH4), a critical cofactor for eNOS, induces uncoupled eNOS activity and impairs angiogenesis in PPHN. Pulmonary artery endothelial cells (PAEC) isolated from fetal lambs with PPHN (HTFL-PAEC) or control lambs (NFL-PAEC) were used to investigate the cellular mechanisms impairing angiogenesis in PPHN. Cellular mechanisms were examined with respect to BH4 levels, GTP-cyclohydrolase-1 (GCH-1) expression, eNOS dimer formation, and eNOS-heat shock protein 90 (hsp90) interactions under basal conditions and after sepiapterin (Sep) supplementation. Cellular levels of BH4, GCH-1 expression, and eNOS dimer formation were decreased in HTFL-PAEC compared with NFL-PAEC. Sep supplementation decreased apoptosis and increased in vitro angiogenesis in HTFL-PAEC and ex vivo pulmonary artery sprouting angiogenesis. Sep also increased cellular BH4 content, NO production, eNOS dimer formation, and eNOS-hsp90 association and decreased the superoxide formation in HTFL-PAEC. These data demonstrate that Sep improves NO production and angiogenic potential of HTFL-PAEC by recoupling eNOS activity. Increasing BH4 levels via Sep supplementation may be an important therapy for improving eNOS function and restoring angiogenesis in PPHN.

Effects of sepiapterin infusion on renal oxygenation and early acute renal injury after suprarenal aortic clamping in rats

Acute kidney injury (AKI) can occur after aortic clamping due to microvascular dysfunction leading to renal hypoxia. In this rat study, we have tested the hypothesis that the administration of the precursor of the nitric oxide synthase essential cofactor tetrahydrobiopterin (BH4) could restore renal oxygenation after ischemia reperfusion (I/R) and prevent AKI. We randomly distributed rats into 4 groups: sham group; ischemia-reperfusion group; I/R + sepiapterin, the precursor of BH4; and I/R + sepiapterin + methotrexate, an inhibitor of the pathway generating BH4 from sepiapterin. Cortical and outer medullary microvascular oxygen pressure, renal oxygen delivery, renal oxygen consumption were measured using dual-wavelength oxygen-dependent quenching phosphorescence techniques during ischemia and throughout 3 hours of reperfusion. Kidney injury was assessed using myeloperoxidase staining for leukocyte infiltration and urine neutrophil gelatinase-associated lipocalin levels. Ischemia reperfusion induced a drop in microvascular PO2 (P < 0.01 vs. Sham, both), which was prevented by the infusion of sepiapterin. Sepiapterin partially prevented the rise in renal oxygen extraction (P < 0.001 vs. I/R). Finally, treatment with sepiapterin prevented renal infiltration by inflammatory cells and decreased urine neutrophil gelatinase-associated lipocalin levels indicating a decrease of renal injury. These effects were blunted when adding methotrexate, except for myeloperoxidase. In conclusion, the administration of sepiapterin can prevent renal hypoxia and AKI after suprarenal aortic clamping in rats.

The molecular mechanism of mammalian NO-synthases: a story of electrons and protons

Since its discovery, nitric oxide synthase (NOS), the enzyme responsible for NO biosynthesis in mammals, has been the subject of extensive investigations regarding its catalytic and molecular mechanisms. These studies reveal the high degree of sophistication of NOS functioning and regulation. However, the precise description of the NOS molecular mechanism and in particular of the oxygen activation chemistry is still lacking. The reaction intermediates implicated in NOS catalysis continue to elude identification and the current working paradigm is increasingly contested. Consequently, the last three years has seen the emergence of several competing models. All these models propose the same global reaction scheme consisting of two successive oxidation reactions but they diverge in the details of their reaction sequence. The major discrepancies concern the number, source and characteristics of proton and electron transfer processes. As a result each model proposes distinct reaction pathways with different implied oxidative species. This review aims to examine the different experimental evidence concerning NOS proton and electron transfer events and the role played by the substrates and cofactors in these processes. The resulting discussion should provide a comparative picture of all potential models for the NOS molecular mechanism.

Protein expression changes induced in murine peritoneal macrophages by Group B Streptococcus

Protein expression changes induced in thioglycolate-elicited peritoneal murine macrophages (M Phi) by infection with type III Group B Streptococcus (GBS) are described. Proteins from control M Phi and M Phi incubated 2 h with live or heat-inactivated GBS were separated by 2-DE. Proteins whose expression was significantly different in infected M Phi, as compared with control cells, were identified by MS/MS analysis. Changes in the expression level of proteins involved in both positive and negative modulation of phagocytic functions, stress response and cell death were induced in M Phi by GBS infection. In particular, expression of enzymes playing a key role in production of reactive oxygen species was lowered in GBS-infected M Phi. Significant alterations in the expression of some metabolic enzymes were also observed, most of the glycolytic and of the pentose-cycle enzymes being down-regulated in M Phi infected with live GBS. Finally, evidence was obtained that GBS infection affects the expression of enzymes or enzyme subunits involved in ATP synthesis and in adenine nucleotides interconversion processes.

Simulated diving after heat stress potentiates the induction of heat shock protein 70 and elevates glutathione in human endothelial cells

Heat stress prior to diving has been shown to confer protection against endothelial damage due to decompression sickness. Several lines of evidence indicate a relation between such protection and the heat shock protein (HSP)70 and HSP90 and the major cellular red-ox determinant, glutathione (GSH). The present study has used human endothelial cells as a model system to investigate how heat stress and simulated diving affect these central cellular defense molecules. The results demonstrated for the first time that a simulated dive at 2.6 MPa (26 bar) had a potentiating effect on the heat-induced expression of HSP70, increasing the HSP70 concentration on average 54 times above control level. In contrast, a simulated dive had no significant potentiating effect on the HSP90 level, which might be due to the higher baseline level of HSP90. Both 2 and 24-h dive had similar effects on the HSP70 and HSP90, suggesting that the observed effects were independent of duration of the dive. The rapid HSP response following a 2-h dive with a decompression time of 5 min might suggest that the effects were due to compression or pressure per se rather than decompression and may involve posttranslational processing of HSP. The exposure order seemed to be critical for the HSP70 response supporting the suggestion that the potentiating effect of dive was not due to de novo synthesis of HSP70. Neither heat shock nor a simulated dive had any significant effect on the intracellular GSH level while a heat shock and a subsequent dive increased the total GSH level approximately 62%. Neither of these conditions seemed to have any effect on the GSH red-ox status.

Endothelial activation and circulating markers of endothelial activation in kidney disease

The recognition of a central role for the endothelium in the development of kidney disease or the development of vascular lesions in patients with established renal dysfunction has led to the emergence of methods to test different aspects of endothelium function, including in endothelium injury and repair. Endothelial-cell activation is associated with the shedding of components of the glycocalyx, adhesion molecules and endothelial microparticles into the circulation. This process may eventually result in the detachment of endothelial cells and recruitment of circulating myeloid and progenitor cells that are involved in vascular remodeling and repair. Circulating markers of endothelium activation may therefore represent novel markers of vessel wall injury. This Review describes the biology of these circulating markers of vessel wall injury, the methodologies used to measure them, and their possible relevance to patients with kidney disease.

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

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

Nitric oxide and oxidative stress in vascular disease

Endothelium-derived nitric oxide (NO) is a paracrine factor that controls vascular tone, inhibits platelet function, prevents adhesion of leukocytes, and reduces proliferation of the intima. An enhanced inactivation and/or reduced synthesis of NO is seen in conjunction with risk factors for cardiovascular disease. This condition, referred to as endothelial dysfunction, can promote vasospasm, thrombosis, vascular inflammation, and proliferation of vascular smooth muscle cells. Vascular oxidative stress with an increased production of reactive oxygen species (ROS) contributes to mechanisms of vascular dysfunction. Oxidative stress is mainly caused by an imbalance between the activity of endogenous pro-oxidative enzymes (such as NADPH oxidase, xanthine oxidase, or the mitochondrial respiratory chain) and anti-oxidative enzymes (such as superoxide dismutase, glutathione peroxidase, heme oxygenase, thioredoxin peroxidase/peroxiredoxin, catalase, and paraoxonase) in favor of the former. Also, small molecular weight antioxidants may play a role in the defense against oxidative stress. Increased ROS concentrations reduce the amount of bioactive NO by chemical inactivation to form toxic peroxynitrite. Peroxynitrite-in turn-can "uncouple" endothelial NO synthase to become a dysfunctional superoxide-generating enzyme that contributes to vascular oxidative stress. Oxidative stress and endothelial dysfunction can promote atherogenesis. Therapeutically, drugs in clinical use such as ACE inhibitors, AT(1) receptor blockers, and statins have pleiotropic actions that can improve endothelial function. Also, dietary polyphenolic antioxidants can reduce oxidative stress, whereas clinical trials with antioxidant vitamins C and E failed to show an improved cardiovascular outcome.

Evidence against tetrahydrobiopterin depletion of vascular tissue exposed to nitric oxide/superoxide or nitroglycerin

Several cardiovascular disorders, including atherosclerosis and tolerance to the antianginal drug nitroglycerin (GTN), may be associated with the generation of superoxide anions, which react with nitric oxide (NO) to yield peroxynitrite. According to a widely held view, oxidation of tetrahydrobiopterin (BH(4)) by peroxynitrite causes uncoupling of endothelial NO synthase (eNOS), resulting in reduced NO bioavailability and endothelial dysfunction under conditions of oxidative stress. In this study we determined the levels of reduced biopterins and endothelial function in cultured cells exposed to peroxynitrite and GTN as well as in blood vessels isolated from GTN-tolerant guinea pigs and rats. BH(4) was rapidly oxidized by peroxynitrite and 3-morpholino sydnonimine (SIN-1) in buffer, but this was prevented by glutathione and not observed in endothelial cells exposed to SIN-1 or GTN. Prolonged treatment of the cells with 0.1 mM GTN caused slow N(G)-nitro-l-arginine-sensitive formation of reactive oxygen species without affecting eNOS activity. Endothelial function and BH(4)/BH(2) levels were identical in blood vessels of control and GTN-tolerant animals. Our results suggest that peroxynitrite-triggered BH(4) oxidation does not occur in endothelial cells or GTN-exposed blood vessels. GTN seems to trigger minor eNOS uncoupling that is unrelated to BH(4) depletion and without observable consequence on eNOS function.

The novel nitric oxide synthase inhibitor 4-amino-tetrahydro-L-biopterine prevents brain edema formation and intracranial hypertension following traumatic brain injury in mice

Brain edema formation, resulting in increased intracranial pressure (ICP), is one of the most deleterious consequences of traumatic brain injury (TBI). Nitric oxide (NO) has previously been shown to be involved in the damage of the blood-brain barrier (BBB) and, thus, in the formation of post-traumatic brain edema; however, this knowledge never resulted in a clinically relevant therapeutic option because available NO synthase inhibitors have serious side effects in man. The aim of the current study was to investigate the therapeutic efficacy of VAS203, a novel tetrahydrobiopterine (BH3)-based NOS inhibitor, in experimental TBI. When added to isolated vessels rings obtained from rat basilar and middle cerebral arteries (n = 32-35) VAS203 showed the same vasoconstrictive effect as the classical NO synthase inhibitor L-(G)-nitro-arginine-methylester (L-NAME). VAS203 passed the BBB both in healthy and traumatized mouse brain (C57/BL6, n = 5 per group) and did not show any systemic side effects at therapeutic concentrations. When administered 30 min after experimental TBI (controlled cortical impact, 2.2 mg/kg/min i.v., n = 7 per group), VAS203 prevented any further increase in ICP or deterioration of cerebral blood flow. This effect was dose-dependent and long-lasting (i.e., 24 h after trauma, brain edema formation was still significantly reduced [-40%, p < 0.008; n = 7 per group] and functional improvements were present up to 7 days after TBI [p < 0.02 on post-trauma day 6; n = 8 per group]). Therefore, VAS203 may represent a promising candidate for the treatment of acute intracranial hypertension following TBI.

The role of nitric oxide in osteoarthritis

Elevated levels of markers of nitric oxide (NO) production are found in osteoarthritic joints suggesting that NO is involved in the pathogenesis of osteoarthritis (OA). In OA, NO mediates many of the destructive effects of interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF-alpha) in the cartilage, and inhibitors of NO synthesis have demonstrated retardation of clinical and histological signs and symptoms in experimentally induced OA and other forms of arthritis. As an important factor in cartilage, the regulation of inducible nitric oxide synthase (iNOS) expression and activity, and the effects of NO are reviewed, especially in relation to the pathogenesis of OA.

Use of vitamins C and E as a prophylactic therapy to prevent postoperative atrial fibrillation

Oxidative stress has been strongly involved in the underlying mechanism of atrial fibrillation, particularly in the arrhythmia occurring in patients undergoing cardiac surgery with extracorporeal circulation (postoperative atrial fibrillation). The ischemia/reperfusion injury thus occurring in the myocardial tissue contributes to the development of tissue remodeling, thought to be responsible for the functional heart impairment. Consequently, structural changes due to the cardiac tissue biomolecules attack by reactive oxygen and/or nitrogen species could account for functional changes in ion channels, transporters, membrane conductance, cytosolic transduction signals, and other events, all associated with the occurrence of arrhythmic consequences. The lack of success and significant side effects of anti-arrhythmic drugs have given rise to attempts aimed to develop alternative novel pharmacologic treatments. On this line, the biological properties of the antioxidant vitamins C and E suggest that they could decrease the vulnerability of the heart to the oxidative damage. Nevertheless, very few studies to assess their anti-arrhythmic effects have been reported in humans. The clinical and experimental evidence supporting the view that the pharmacological use of antioxidant vitamins could contribute to prevent postoperative atrial fibrillation is presented.