Zinc-binding cysteines: diverse functions and structural motifs

Cysteine residues are known to perform essential functions within proteins, including binding to various metal ions. In particular, cysteine residues can display high affinity toward zinc ions (Zn2+), and these resulting Zn2+-cysteine complexes are critical mediators of protein structure, catalysis and regulation. Recent advances in both experimental and theoretical platforms have accelerated the identification and functional characterization of Zn2+-bound cysteines. Zn2+-cysteine complexes have been observed across diverse protein classes and are known to facilitate a variety of cellular processes. Here, we highlight the structural characteristics and diverse functional roles of Zn2+-cysteine complexes in proteins and describe structural, computational and chemical proteomic technologies that have enabled the global discovery of novel Zn2+-binding cysteines.

Detection of key enzymes, free radical reaction products and activated signaling molecules as biomarkers of cell damage induced by benzo[a]pyrene in human keratinocytes

Benzo[a]pyrene (BaP) is a known carcinogenic and cell damaging agent. The underlying cell damaging pathomechanisms have not been totally revealed. Especially BaP-related induction of oxidative and nitrosative stress has not been previously investigated in detail. The presented study investigated these effects in order to elucidate the pathomechanism and as well to identify potential biological markers that may indicate a BaP exposure. Human immortalized keratinocytes (HaCaT cells) were exposed to BaP (1 μM) for either 5 min or 6 h, respectively. BaP-induced cellular damage was evaluated by immunocytochemistry analysis of multiple signaling cascades (e.g. apoptosis, Akt, MAPK, NOS, nitrotyrosine and 8-isoprostane formation), detection of nitrosative stress using diaminofluorescein (DAF-FM) and oxidative stress using 3' -(p-aminophenyl)fluorescein (APF). Our results show that BaP exposure significantly enhanced NO and ROS productions in HaCaT cells. BaP led to eNOS-phosphorylation at Ser(1177), Thr(495) and Ser(116) residues. Using specific inhibitors, we found that the Erk1/2 pathways seemed to have strong impact on eNOS phosphorylation. In addition, BaP-induced apoptosis was observed by caspase-3 activation and PARP cleavage. Our results suggest that BaP mediates its toxic effect in keratinocytes through oxidative and nitrosative stress which is accompanied by complex changes of eNOS phosphorylation and changes of Akt and MAPK pathways.

Redox regulation of endothelial cell fate

Endothelial cells (ECs) are present throughout blood vessels and have variable roles in both physiological and pathological settings. EC fate is altered and regulated by several key factors in physiological or pathological conditions. Reactive nitrogen species and reactive oxygen species derived from NAD(P)H oxidases, mitochondria, or nitric oxide-producing enzymes are not only cytotoxic but also compose a signaling network in the redox system. The formation, actions, key molecular interactions, and physiological and pathological relevance of redox signals in ECs remain unclear. We review the identities, sources, and biological actions of oxidants and reductants produced during EC function or dysfunction. Further, we discuss how ECs shape key redox sensors and examine the biological functions, transcriptional responses, and post-translational modifications evoked by the redox system in ECs. We summarize recent findings regarding the mechanisms by which redox signals regulate the fate of ECs and address the outcome of altered EC fate in health and disease. Future studies will examine if the redox biology of ECs can be targeted in pathophysiological conditions.

Nitric oxide synthase regulation of cardiac excitation-contraction coupling in health and disease

Significant advances in our understanding of the ability of nitric oxide synthases (NOS) to modulate cardiac function have provided key insights into the role NOS play in the regulation of excitation-contraction (EC) coupling in health and disease. Through both cGMP-dependent and cGMP-independent (e.g. S-nitrosylation) mechanisms, NOS have the ability to alter intracellular Ca(2+) handling and the myofilament response to Ca(2+), thereby impacting the systolic and diastolic performance of the myocardium. Findings from experiments using nitric oxide (NO) donors and NOS inhibition or gene deletion clearly implicate dysfunctional NOS as a critical contributor to many cardiovascular disease states. However, studies to date have only partially addressed NOS isoform-specific effects and, more importantly, how subcellular localization of NOS influences ion channels involved in myocardial EC coupling and excitability. In this review, we focus on the contribution of each NOS isoform to cardiac dysfunction and on the role of uncoupled NOS activity in common cardiac disease states, including heart failure, diabetic cardiomyopathy, ischemia/reperfusion injury and atrial fibrillation. We also review evidence that clearly indicates the importance of NO in cardioprotection. This article is part of a Special Issue entitled "Redox Signalling in the Cardiovascular System".

Isoproterenol induces vascular oxidative stress and endothelial dysfunction via a Giα-coupled β2-adrenoceptor signaling pathway

OBJECTIVE

Sustained β-adrenergic stimulation is a hallmark of sympathetic hyperactivity in cardiovascular diseases. It is associated with oxidative stress and altered vasoconstrictor tone. This study investigated the β-adrenoceptor subtype and the signaling pathways implicated in the vascular effects of β-adrenoceptor overactivation.

METHODS AND RESULTS

Mice lacking the β1- or β2-adrenoceptor subtype (β1KO, β2KO) and wild-type (WT) were treated with isoproterenol (ISO, 15 μg.g(-1) x day(-1), 7 days). ISO significantly enhanced the maximal vasoconstrictor response (Emax) of the aorta to phenylephrine in WT (+34%) and β1KO mice (+35%) but not in β2KO mice. The nitric oxide synthase (NOS) inhibitor L-NAME abolished the differences in phenylephrine response between the groups, suggesting that ISO impaired basal NO availability in the aorta of WT and β1KO mice. Superoxide dismutase (SOD), pertussis toxin (PTx) or PD 98,059 (p-ERK 1/2 inhibitor) incubation reversed the hypercontractility of aortic rings from ISO-treated WT mice; aortic contraction of ISO-treated β2KO mice was not altered. Immunoblotting revealed increased aortic expression of Giα-3 protein (+50%) and phosphorylated ERK1/2 (+90%) and decreased eNOS dimer/monomer ratio in ISO-treated WT mice. ISO enhanced the fluorescence response to dihydroethidium (+100%) in aortas from WT mice, indicating oxidative stress that was normalized by SOD, PTx and L-NAME. The ISO effects were abolished in β2KO mice.

CONCLUSIONS

The β2-adrenoceptor/Giα signaling pathway is implicated in the enhanced vasoconstrictor response and eNOS uncoupling-mediated oxidative stress due to ISO treatment. Thus, long-term β2-AR activation might results in endothelial dysfunction.

Endothelial nitric oxide synthase uncoupling and microvascular dysfunction in the mesentery of mice deficient in α-galactosidase A

A defect in the gene for the lysosomal enzyme α-galactosidase A (Gla) results in globotriaosylceramide (Gb3) accumulation in Fabry disease and leads to premature death from cardiac and cerebrovascular events. However, gastrointestinal symptoms are often first observed during childhood in these patients and are not well understood. In this study, we demonstrate an age-dependent microvasculopathy of the mesenteric artery (MA) in a murine model of Fabry disease (Gla-knockout mice) resulting from dysregulation of the vascular homeostatic enzyme endothelial nitric oxide synthase (eNOS). The progressive accumulation of Gb3 in the MA was confirmed by thin-layer chromatographic analysis. A total absence of endothelium-dependent dilation was observed in MAs from mice at 8 mo of age, while suppression of ACh-mediated vasodilation was evident from 2 mo of age. Endothelium-independent dilation with sodium nitroprusside was normal compared with age-matched wild-type mice. The microvascular defect in MAs from Fabry mice was endothelium-dependent and associated with suppression of the active homodimer of eNOS. Phosphorylation of eNOS at the major activation site (Ser(1179)) was significantly downregulated, while phosphorylation at the major inhibitory site (Thr(495)) was remarkably enhanced in MAs from aged Fabry mice. These profound alterations in eNOS bioavailability at 8 mo of age were observed in parallel with high levels of 3-nitrotyrosine, suggesting increased reactive oxygen species along with eNOS uncoupling in this vascular bed. Overall, the mesenteric microvessels in the setting of Fabry disease were observed to have an early and profound endothelial dysfunction associated with elevated reactive nitrogen species and decreased nitric oxide bioavailability.

Protein engineering to develop a redox insensitive endothelial nitric oxide synthase

The zinc tetrathiolate (ZnS₄) cluster is an important structural feature of endothelial nitric oxide synthase (eNOS). The cluster is located on the dimeric interface and four cysteine residues (C94 and C99 from two adjacent subunits) form a cluster with a Zn ion in the center of a tetrahedral configuration. Due to its high sensitivity to oxidants this cluster is responsible for eNOS dimer destabilization during periods of redox stress. In this work we utilized site directed mutagenesis to replace the redox sensitive cysteine residues in the ZnS₄ cluster with redox stable tetra-arginines. Our data indicate that this C94R/C99R eNOS mutant is active. In addition, this mutant protein is insensitive to dimer disruption and inhibition when challenged with hydrogen peroxide (H₂O₂). Further, the overexpression of the C94R/C99R mutant preserved the angiogenic response in endothelial cells challenged with H₂O₂. The over-expression of the C94R/C99R mutant preserved the ability of endothelial cells to migrate towards vascular endothelial growth factor (VEGF) and preserved the endothelial monolayer in a scratch wound assay. We propose that this dimer stable eNOS mutant could be utilized in the treatment of diseases in which there is eNOS dysfunction due to high levels of oxidative stress.

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The ZnS₄ cluster is an important structural feature of eNOS.

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This cluster is responsible for eNOS dimer destabilization during redox stress.

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Site directed mutagenesis replaced ZnS₄ clusters with redox stable tetra-arginines.

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This eNOS mutant is insensitive to dimer disruption during redox stress.

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This eNOS mutant continues to produce NO during redox stress.

Targeting NOS as a therapeutic approach for heart failure

Nitric oxide is a key signaling molecule in the heart and is produced endogenously by three isoforms of nitric oxide synthase, neuronal NOS (NOS1), endothelial NOS (NOS3), and inducible NOS (NOS2). Nitric oxide signals via cGMP-dependent or independent pathways to modulate downstream proteins via specific post translational modifications (i.e. cGMP-dependent protein kinase phosphorylation, S-nitrosylation, etc.). Dysfunction of NOS (i.e. altered expression, location, coupling, activity, etc.) exists in various cardiac disease conditions, such as heart failure, contributing to the contractile dysfunction, adverse remodeling, and hypertrophy. This review will focus on the signaling pathways of each NOS isoform during health and disease, and discuss current and potential therapeutic approaches targeting nitric oxide signaling to treat heart disease.

The smoking-associated oxidant hypothiocyanous acid induces endothelial nitric oxide synthase dysfunction

The smoking-associated oxidant hypothiocyanous acid converts active dimeric endothelial cell nitric oxide synthase into its monomer form, decreases enzyme activity and releases Zn2+. This is ascribed to targeting of the critical Zn2+–thiol cluster by this thiol-specific oxidant.

Peroxynitrite-dependent zinc release and inactivation of guanosine 5'-triphosphate cyclohydrolase 1 instigate its ubiquitination in diabetes

Aberrant degradation of guanosine 5'-triphosphate cyclohydrolase 1 (GTPCH1) with consequent deficiency of tetrahydrobiopterin is considered the primary cause for endothelial dysfunction in diabetes. How GTPCH1 becomes susceptible to the degradation remains unknown. We hypothesized that oxidation and release of the zinc ion by peroxynitrite (ONOO(-)), a potent oxidant generated by nitric oxide and superoxide anions, instigates GTPCH1 ubiquitination and degradation. Zinc contents, GTPCH1 ubiquitination, and GTPCH1 activity were assayed in purified GTPCH1, endothelial cells, and hearts from diabetic mice. Exogenous ONOO(-) dose-dependently released zinc, inhibited its activity, and increased the ubiquitin binding affinity of GTPCH1 in vitro and in endothelial cells. Consistently, high glucose (30 mmol/L) inhibited GTPCH1 activity with increased ubiquitination, which was inhibited by antioxidants. Furthermore, mutation of the zinc-binding cysteine (141) (C141R or C141A) significantly reduced GTPCH1 activity and reduced its half-life but increased GTPCH1 ubiquitination, indicating an essential role of the zinc ion in maintaining the catalytic activity and stability of GTPCH1. Finally, GTPCH1 ubiquitination and degradation markedly increased in parallel with decreased GTPCH1 activity in the aortas and hearts of diabetic mice, both of which were attenuated by the inhibitors of ONOO(-) in mice in vivo. Taken together, we conclude that ONOO(-) releases zinc and inhibits GTPCH1, resulting in its ubiquitination and degradation of the enzyme.

Biopterin metabolism and eNOS expression during hypoxic pulmonary hypertension in mice

Tetrahydrobiopterin (BH4), which fosters the formation of and stabilizes endothelial NO synthase (eNOS) as an active dimer, tightly regulates eNOS coupling / uncoupling. Moreover, studies conducted in genetically-modified models demonstrate that BH4 pulmonary deficiency is a key determinant in the pathogenesis of pulmonary hypertension. The present study thus investigates biopterin metabolism and eNOS expression, as well as the effect of sepiapterin (a precursor of BH4) and eNOS gene deletion, in a mice model of hypoxic pulmonary hypertension. In lungs, chronic hypoxia increased BH4 levels and eNOS expression, without modifying dihydrobiopterin (BH2, the oxidation product of BH4) levels, GTP cyclohydrolase-1 or dihydrofolate reductase expression (two key enzymes regulating BH4 availability). In intrapulmonary arteries, chronic hypoxia also increased expression of eNOS, but did not induce destabilisation of eNOS dimers into monomers. In hypoxic mice, sepiapterin prevented increase in right ventricular systolic pressure and right ventricular hypertrophy, whereas it modified neither remodelling nor alteration in vasomotor responses (hyper-responsiveness to phenylephrine, decrease in endothelium-dependent relaxation to acetylcholine) in intrapulmonary arteries. Finally, deletion of eNOS gene partially prevented hypoxia-induced increase in right ventricular systolic pressure, right ventricular hypertrophy and remodelling of intrapulmonary arteries. Collectively, these data demonstrate the absence of BH4/BH2 changes and eNOS dimer destabilisation, which may induce eNOS uncoupling during hypoxia-induced pulmonary hypertension. Thus, even though eNOS gene deletion and sepiapterin treatment exert protective effects on hypoxia-induced pulmonary vascular remodelling, increase on right ventricular pressure and / or right ventricular hypertrophy, these effects appear unrelated to biopterin-dependent eNOS uncoupling within pulmonary vasculature of hypoxic wild-type mice.

A pivotal role for tryptophan 447 in enzymatic coupling of human endothelial nitric oxide synthase (eNOS): effects on tetrahydrobiopterin-dependent catalysis and eNOS dimerization

Tetrahydrobiopterin (BH4) is a required cofactor for the synthesis of NO by NOS. Bioavailability of BH4 is a critical factor in regulating the balance between NO and superoxide production by endothelial NOS (eNOS coupling). Crystal structures of the mouse inducible NOS oxygenase domain reveal a homologous BH4-binding site located in the dimer interface and a conserved tryptophan residue that engages in hydrogen bonding or aromatic stacking interactions with the BH4 ring. The role of this residue in eNOS coupling remains unexplored. We overexpressed human eNOS W447A and W447F mutants in novel cell lines with tetracycline-regulated expression of human GTP cyclohydrolase I, the rate-limiting enzyme in BH4 synthesis, to determine the importance of BH4 and Trp-447 in eNOS uncoupling. NO production was abolished in eNOS-W447A cells and diminished in cells expressing W447F, despite high BH4 levels. eNOS-derived superoxide production was significantly elevated in W447A and W447F versus wild-type eNOS, and this was sufficient to oxidize BH4 to 7,8-dihydrobiopterin. In uncoupled, BH4-deficient cells, the deleterious effects of W447A mutation were greatly exacerbated, resulting in further attenuation of NO and greatly increased superoxide production. eNOS dimerization was attenuated in W447A eNOS cells and further reduced in BH4-deficient cells, as demonstrated using a novel split Renilla luciferase biosensor. Reduction of cellular BH4 levels resulted in a switch from an eNOS dimer to an eNOS monomer. These data reveal a key role for Trp-447 in determining NO versus superoxide production by eNOS, by effects on BH4-dependent catalysis, and by modulating eNOS dimer formation.

Dietary zinc intake is inversely associated with systolic blood pressure in young obese women

Zinc may participate in blood pressure regulation and in the pathogenesis of hypertension. The study examined the relationship between zinc status and blood pressure in obese Korean women. Forty obese women (body mass index (BMI) ≥ 25 kg/m(2)) aged 19-28 years participated in this study. Zinc intake was estimated from one 24 hour recall and 2-day diet records. Serum and urinary zinc concentrations were determined by atomic absorbance spectrophotometry. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured using an automatic sphygmometer. Metabolic variables, such as waist circumference, triglyceride, high density lipoprotein (HDL) cholesterol, fasting glucose, and fasting insulin, were also measured. Dietary zinc intake of obese women was averagely 7.5 mg/day. Serum zinc and urinary zinc concentrations were 13.4 µmol/L and 378.7 µg/day, respectively. Averages of SBP and DBP were 119 mmHg and 78 mmHg. Dietary zinc intake was negatively correlated with SBP after adjusting for energy intake (P < 0.05), but serum and urinary zinc concentrations were not found to be correlated with SBP or DBP. Multivariate linear regression analysis showed that dietary zinc intake was inversely associated with SBP in obese women after adjusting for body weight, energy intake and sodium intake (P = 0.0145). The results show that dietary zinc intake may be an independent risk factor of elevated SBP in obese Korean women.

Nox4 NADPH oxidase mediates peroxynitrite-dependent uncoupling of endothelial nitric-oxide synthase and fibronectin expression in response to angiotensin II: role of mitochondrial reactive oxygen species

Activation of glomerular mesangial cells (MCs) by angiotensin II (Ang II) leads to extracellular matrix accumulation. Here, we demonstrate that, in MCs, Ang II induces endothelial nitric-oxide synthase (eNOS) uncoupling with enhanced generation of reactive oxygen species (ROS) and decreased production of NO. Ang II promotes a rapid increase in 3-nitrotyrosine formation, and uric acid attenuates Ang II-induced decrease in NO bioavailability, demonstrating that peroxynitrite mediates the effects of Ang II on eNOS dysfunction. Ang II rapidly up-regulates Nox4 protein. Inhibition of Nox4 abolishes the increase in ROS and peroxynitrite generation as well as eNOS uncoupling triggered by Ang II, indicating that Nox4 is upstream of eNOS. This pathway contributes to Ang II-mediated fibronectin accumulation in MCs. Ang II also elicits an increase in mitochondrial abundance of Nox4 protein, and the oxidase contributes to ROS production in mitochondria. Overexpression of mitochondrial manganese superoxide dismutase prevents the stimulatory effects of Ang II on mitochondrial ROS production, loss of NO availability, and MC fibronectin accumulation, whereas manganese superoxide dismutase depletion increases mitochondrial ROS, NO deficiency, and fibronectin synthesis basally and in cells exposed to Ang II. This work provides the first evidence that uncoupled eNOS is responsible for Ang II-induced MC fibronectin accumulation and identifies Nox4 and mitochondrial ROS as mediators of eNOS dysfunction. These data shed light on molecular processes underlying the oxidative signaling cascade engaged by Ang II and identify potential targets for intervention to prevent renal fibrosis.

Redox signaling in cardiovascular health and disease

Spatiotemporal regulation of the activity of a vast array of intracellular proteins and signaling pathways by reactive oxygen species (ROS) governs normal cardiovascular function. However, data from experimental and animal studies strongly support that dysregulated redox signaling, resulting from hyperactivation of various cellular oxidases or mitochondrial dysfunction, is integral to the pathogenesis and progression of cardiovascular disease (CVD). In this review, we address how redox signaling modulates the protein function, the various sources of increased oxidative stress in CVD, and the labyrinth of redox-sensitive molecular mechanisms involved in the development of atherosclerosis, hypertension, cardiac hypertrophy and heart failure, and ischemia-reperfusion injury. Advances in redox biology and pharmacology for inhibiting ROS production in specific cell types and subcellular organelles combined with the development of nanotechnology-based new in vivo imaging systems and targeted drug delivery mechanisms may enable fine-tuning of redox signaling for the treatment and prevention of CVD.

Genetic elimination of eNOS reduces secondary complications of experimental subarachnoid hemorrhage

Delayed complications of subarachnoid hemorrhage (SAH) such as angiographic vasospasm, cortical spreading ischemia, microcirculatory dysfunction, and microthrombosis are reported in both patients and animal models of SAH. We demonstrated previously that SAH is associated with increased oxidative stress in the brain parenchyma, and that this correlates with dysfunction of endothelial nitric oxide synthase (eNOS) (homodimeric uncoupling). Uncoupling of eNOS exacerbated oxidative stress and enhanced nitric oxide (NO) depletion, and was associated with multiple secondary complications such as microthrombosis, neuronal apoptosis, and release of reactive oxygen species. Thus, we hypothesized that genetic abbrogation of eNOS would confer a beneficial effect on the brain after SAH. Using a prechiasmatic injection model of SAH, we show here that eNOS knockout (KO) significantly alleviates vasospasm of the middle cerebral artery and reduces superoxide production. Endothelial nitric oxide synthase KO also affected other nitric oxide synthase isoforms. It significantly increases neuron nitric oxide synthase expression but has no effect on inducible nitric oxide synthase. Endothelial nitric oxide synthase KO decreases Zn(2+) release after SAH, reduces microthrombi formation, and prevent neuronal degeneration. This work is consistent with our findings where, after SAH, increased oxidative stress can uncouple eNOS via Zn(2+) thiolate oxidation, or theoretically by depletion or oxidation of tetrahydrobiopterin, resulting in a paradoxical release of superoxide anion radical, further exacerbating oxidative stress and microvascular damage.

Sestrin 2 and AMPK connect hyperglycemia to Nox4-dependent endothelial nitric oxide synthase uncoupling and matrix protein expression

Mesangial matrix accumulation is an early feature of glomerular pathology in diabetes. Oxidative stress plays a critical role in hyperglycemia-induced glomerular injury. Here, we demonstrate that, in glomerular mesangial cells (MCs), endothelial nitric oxide synthase (eNOS) is uncoupled upon exposure to high glucose (HG), with enhanced generation of reactive oxygen species (ROS) and decreased production of nitric oxide. Peroxynitrite mediates the effects of HG on eNOS dysfunction. HG upregulates Nox4 protein, and inhibition of Nox4 abrogates the increase in ROS and peroxynitrite generation, as well as the eNOS uncoupling triggered by HG, demonstrating that Nox4 functions upstream from eNOS. Importantly, this pathway contributes to HG-induced MC fibronectin accumulation. Nox4-mediated eNOS dysfunction was confirmed in glomeruli of a rat model of type 1 diabetes. Sestrin 2-dependent AMP-activated protein kinase (AMPK) activation attenuates HG-induced MC fibronectin synthesis through blockade of Nox4-dependent ROS and peroxynitrite generation, with subsequent eNOS uncoupling. We also find that HG negatively regulates sestrin 2 and AMPK, thereby promoting Nox4-mediated eNOS dysfunction and increased fibronectin. These data identify a protective function for sestrin 2/AMPK and potential targets for intervention to prevent fibrotic injury in diabetes.

Nitric oxide synthase dysfunction contributes to impaired cerebroarteriolar reactivity in experimental cerebral malaria

Cerebrovascular dysfunction plays a key role in the pathogenesis of cerebral malaria. In experimental cerebral malaria (ECM) induced by Plasmodium berghei ANKA, cerebrovascular dysfunction characterized by vascular constriction, occlusion and damage results in impaired perfusion and reduced cerebral blood flow and oxygenation, and has been linked to low nitric oxide (NO) bioavailability. Here, we directly assessed cerebrovascular function in ECM using a novel cranial window method for intravital microscopy of the pial microcirculation and probed the role of NOS isoforms and phosphorylation patterns in the impaired vascular responses. We show that pial arteriolar responses to endothelial NOS (eNOS) and neuronal NOS (nNOS) agonists (Acetylcholine (ACh) and N-Methyl-D-Aspartate (NMDA)) were blunted in mice with ECM, and could be partially recovered by exogenous supplementation of tetrahydrobiopterin (BH4). Pial arterioles in non-ECM mice infected by Plasmodium berghei NK65 remained relatively responsive to the agonists and were not significantly affected by BH4 treatment. These findings, together with the observed blunting of NO production upon stimulation by the agonists, decrease in total NOS activity, augmentation of lipid peroxidation levels, upregulation of eNOS protein expression, and increase in eNOS and nNOS monomerization in the brain during ECM development strongly indicate a state of eNOS/nNOS uncoupling likely mediated by oxidative stress. Furthermore, the downregulation of Serine 1176 (S1176) phosphorylation of eNOS, which correlated with a decrease in cerebrovascular wall shear stress, implicates hemorheological disturbances in eNOS dysfunction in ECM. Finally, pial arterioles responded to superfusion with the NO donor, S-Nitroso-L-glutathione (GSNO), but with decreased intensity, indicating that not only NO production but also signaling is perturbed during ECM. Therefore, the pathological impairment of eNOS and nNOS functions contribute importantly to cerebrovascular dysfunction in ECM and the recovery of intrinsic functionality of NOS to increase NO bioavailability and restore vascular health represents a target for ECM treatment.

Apolipoprotein A-1 mimetic D-4F enhances isoflurane-induced eNOS signaling and cardioprotection during acute hyperglycemia

Acute hyperglycemia (AHG) decreases the availability of nitric oxide (NO) and impairs anesthetic preconditioning (APC)-elicited protection against myocardial infarction. We investigated whether D-4F, an apolipoprotein A-1 mimetic, rescues the myocardium by promoting APC-induced endothelial NO signaling during AHG. Myocardial infarct size was measured in mice in the absence or presence of APC [isoflurane (1.4%)] with or without AHG [dextrose (2 g/kg ip)] and D-4F (0.12 or 0.6 mg/kg ip). NO production, superoxide generation, protein compartmentalization, and posttranslational endothelial NO synthase (eNOS) modifications were assessed in human coronary artery endothelial cells cultured in 5.5 or 20 mM glucose with or without isoflurane (0.5 mM) in the presence or absence of D-4F (0.5 μg/ml). Myocardial infarct size was significantly decreased by APC (36 ± 3% of risk area) compared with control (54 ± 3%) in the absence, but not presence, of AHG (49 ± 4%). D-4F restored the cardioprotective effect of APC during AHG (36 ± 3% and 30 ± 3%, 0.12 and 0.6 mg/kg, respectively), although D-4F alone had no effect on infarct size (53 ± 3%). Isoflurane promoted caveolin-1 and eNOS compartmentalization within endothelial cell caveolae and eNOS dimerization, concomitant with increased NO production (411 ± 28 vs. 68 ± 10 pmol/mg protein in control). These actions were attenuated by AHG (NO production: 264 ± 18 pmol/mg protein). D-4F reduced superoxide generation and enhanced caveolin-1 and eNOS caveolar compartmentalization and posttranslational eNOS modifications, thus restoring NO production during isoflurane and AHG (418 ± 36 pmol/mg protein). In conclusion, D-4F restored the cardioprotective effect of APC during AHG, possibly by decreasing superoxide generation, which promoted isoflurane-induced eNOS signaling and NO biosynthesis.

Reduced plasma zinc levels, lipid peroxidation, and inflammation biomarkers levels in hemodialysis patients: implications to cardiovascular mortality

Despite the fact that low plasma zinc (Zn) levels play important roles in the oxidative stress, the relationships between lipid peroxidation and inflammation biomarkers with low plasma Zn levels have not been investigated in chronic kidney disease (CKD) patients. The aim of this study was to evaluate the Zn plasma levels, electronegative LDL [LDL(-)] levels, and inflammation markers as predictors of cardiovascular (CV) mortality in hemodialysis (HD) patients. Forty-five HD patients (28 men, 54.2 ± 12.7 years, 62.2 ± 51.4 months on dialysis and BMI 24.3 ± 4.1 kg/m(2)) were studied and compared to 20 healthy individuals (9 men, 51.6 ± 15.6 years, BMI 25.2 ± 3.9 kg/m(2)) and followed for 24 months to investigate the risks for CV mortality. LDL(-) levels were measured by ELISA, plasma Zn levels by atomic absorption spectrophotometry, C-reactive protein (CRP) level by immunoturbidimetric method, and tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), monocyte chemotactic protein-1 (MCP-1), and plasminogen activator inhibitor-1 (PAI-1) levels by a multiplex assay kit. HD patients presented low plasma Zn levels (54.9 ± 16.1 μg/dL) and high-LDL(-) (0.18 ± 0.12 U/L) and TNF-α (5.5 ± 2.2 pg/mL) levels when compared to healthy subjects (78.8 ± 9.4μ g/dL, 0.10 ± 0.08U/L, 2.4 ± 1.1 pg/mL, respectively, p < 0.05). Zn plasma levels were negatively correlated to TNF-α (r = -0.49; p = 0.0001) and LDL(-) (r = -0.33; p = 0.008). During the 2 years, 24.4% of the patients died, all due to CV disease. Analysis by the Cox model showed that high CRP, TNF-α, IL-6 levels, and long duration of HD were significant predictors of mortality. In conclusion, reduced Zn levels were associated with lipid peroxidation and inflammation, and we confirm here in a Brazilian cohort of HD patients that inflammation markers are strong predictors of CV death.

Mechanisms of lipotoxicity in the cardiovascular system

Cardiovascular diseases account for approximately one third of all deaths globally. Obese and diabetic patients have a high likelihood of dying from complications associated with cardiovascular dysfunction. Obesity and diabetes increase circulating lipids that upon tissue uptake, may be stored as triglyceride, or may be metabolized in other pathways, leading to the generation of toxic intermediates. Excess lipid utilization or activation of signaling pathways by lipid metabolites may disrupt cellular homeostasis and contribute to cell death, defining the concept of lipotoxicity. Lipotoxicity occurs in multiple organs, including cardiac and vascular tissues, and a number of specific mechanisms have been proposed to explain lipotoxic tissue injury. In addition, recent data suggests that increased tissue lipids may also be protective in certain contexts. This review will highlight recent progress toward elucidating the relationship between nutrient oversupply, lipotoxicity, and cardiovascular dysfunction. The review will focus in two sections on the vasculature and cardiomyocytes respectively.

Chronic oxidative-nitrosative stress impairs coronary vasodilation in metabolic syndrome model rats

Metabolic syndrome (MetS) is a combination of clinical disorders that together increase the risk for cardiovascular disease and diabetes. SHRSP.Z-Lepr(fa)/IzmDmcr (SHRSP.ZF) rats with MetS show impaired nitric oxide-mediated relaxation in coronary and mesenteric arteries, and angiotensin II receptor type 1 blockers protect against dysfunction and oxidative-nitrosative stress independently of metabolic effects. We hypothesize that superoxide contributes to functional deterioration in SHRSP.ZF rats. To test our hypothesis, we studied effects of treatment with tempol, a membrane-permeable radical scavenger, on impaired vasodilation in SHRSP.ZF rats. Tempol did not alter body weight, high blood pressure, or metabolic abnormalities, but prevented impairment of acetylcholine-induced and nitroprusside-induced vasodilation in the coronary and mesenteric arteries. Furthermore, tempol reduced the levels of serum thiobarbituric acid reactive substance (TBARS) and 3-nitrotyrosine content in mesenteric arteries. Systemic administration of tempol elevated the expression of soluble guanylate cyclase (sGC) above basal levels in mesenteric arteries of SHRSP.ZF rats. However, acute treatment with tempol or ebselen, a peroxynitrite scavenger, did not ameliorate impaired relaxation of isolated mesenteric arteries. No nitration of tyrosine residues in sGC was observed; however, sGC mRNA expression levels in the arteries of SHRSP.ZF rats were lower than those in the arteries of Wistar-Kyoto rats. Levels of Thr(496)- and Ser(1177)-phosphorylated endothelial nitric oxide synthase (eNOS) were lower in arteries of SHRSP.ZF rats, and acetylcholine decreased Thr(496)-phosphorylated eNOS levels. These results indicated that prolonged superoxide production, leading to oxidative-nitrosative stress, was associated with impaired vasodilation in SHRSP.ZF rats with MetS. Down-regulated sGC expression may be linked to dysfunction, while reduced NO bioavailability/eNOS activity and modified sGC activity due to superoxide production were excluded as pivotal mechanisms.

Gene therapy for the prevention of vein graft disease

Ischemic cardiovascular disease remains the leading cause of death worldwide. Despite advances in the medical management of atherosclerosis over the past several decades, many patients require arterial revascularization to reduce mortality and alleviate ischemic symptoms. Technological advancements have led to dramatic increases in the use of percutaneous and endovascular approaches, yet surgical revascularization (bypass surgery) with autologous vein grafts remains a mainstay of therapy for both coronary and peripheral artery disease. Although bypass surgery is highly efficacious in the short term, long-term outcomes are limited by relatively high failure rates as a result of intimal hyperplasia, which is a common feature of vein graft disease. The supply of native veins is limited, and many individuals require multiple grafts and repeat procedures. The need to prevent vein graft failure has led to great interest in gene therapy approaches to this problem. Bypass grafting presents an ideal opportunity for gene therapy, as surgically harvested vein grafts can be treated with gene delivery vectors ex vivo, thereby maximizing gene delivery while minimizing the potential for systemic toxicity and targeting the pathogenesis of vein graft disease at its onset. Here we will review the pathogenesis of vein graft disease and discuss vector delivery strategies and potential molecular targets for its prevention. We will summarize the preclinical and clinical literature on gene therapy in vein grafting and discuss additional considerations for future therapies to prevent vein graft disease.

Lipotoxicity contributes to endothelial dysfunction: a focus on the contribution from ceramide

Cardiovascular complications are the leading causes of morbidity and mortality in individuals with obesity, type 2 diabetes mellitus (T2DM), and insulin resistance. Complications include pathologies specific to large (atherosclerosis, cardiomyopathy) and small (retinopathy, nephropathy, neuropathy) vessels. Common among all of these pathologies is an altered endothelial cell phenotype i.e., endothelial dysfunction. A crucial aspect of endothelial dysfunction is reduced nitric oxide (NO) bioavailability. Hyperglycemia, oxidative stress, activation of the renin-angiotensin system, and increased pro-inflammatory cytokines are systemic disturbances in individuals with obesity, T2DM, and insulin resistance and each of these contribute independently and synergistically to decreasing NO bioavailability. This review will examine the contribution from elevated circulating fatty acids in these subjects that lead to lipotoxicity. Particular focus will be placed on the fatty acid metabolite ceramide.

Reciprocal regulation of the nitric oxide and cyclooxygenase pathway in pathophysiology: relevance and clinical implications

The nitric oxide (NO) and cyclooxygenase (COX) pathways share a number of similarities. Nitric oxide is the mediator generated from the NO synthase (NOS) pathway, and COX converts arachidonic acid to prostaglandins, prostacyclin, and thromboxane A(2). Two major forms of NOS and COX have been identified to date. The constitutive isoforms critically regulate several physiological states. The inducible isoforms are overexpressed during inflammation in a variety of cells, producing large amounts of NO and prostaglandins, which may underlie pathological processes. The cross-talk between the COX and NOS pathways was initially reported by Salvemini and colleagues in 1993, when they demonstrated in a series of in vitro and in vivo studies that NO activates the COX enzymes to produce increased amounts of prostaglandins. Those studies led to the concept that COX enzymes represent important endogenous "receptor" targets for amplifying or modulating the multifaceted roles of NO in physiology and pathology. Since then, numerous studies have furthered our mechanistic understanding of these interactions in pathophysiological settings and delineated potential clinical outcomes. In addition, emerging evidence suggests that the canonical nitroxidative species (NO, superoxide, and/or peroxynitrite) modulate biosynthesis of prostaglandins through non-COX-related pathways. This article provides a comprehensive state-of-the art overview in this area.

Zinc homeostasis in the metabolic syndrome and diabetes

Zinc (Zn) is an essential mineral that is required for various cellular functions. Zn dyshomeostasis always is related to certain disorders such as metabolic syndrome, diabetes and diabetic complications. The associations of Zn with metabolic syndrome, diabetes and diabetic complications, thus, stem from the multiple roles of Zn: (1) a constructive component of many important enzymes or proteins, (2) a requirement for insulin storage and secretion, (3) a direct or indirect antioxidant action, and (4) an insulin-like action. However, whether there is a clear cause-and-effect relationship of Zn with metabolic syndrome, diabetes, or diabetic complications remains unclear. In fact, it is known that Zn deficiency is a common phenomenon in diabetic patients. Chronic low intake of Zn was associated with the increased risk of diabetes and diabetes also impairs Zn metabolism. Theoretically Zn supplementation should prevent the metabolic syndrome, diabetes, and diabetic complications; however, limited available data are not always supportive of the above notion. Therefore, this review has tried to summarize these pieces of available information, possible mechanisms by which Zn prevents the metabolic syndrome, diabetes, and diabetic complications. In the final part, what are the current issues for Zn supplementation were also discussed.

Vascular aging: chronic oxidative stress and impairment of redox signaling-consequences for vascular homeostasis and disease

Characteristic morphological and molecular alterations such as vessel wall thickening and reduction of nitric oxide occur in the aging vasculature leading to the gradual loss of vascular homeostasis. Consequently, the risk of developing acute and chronic cardiovascular diseases increases with age. Current research of the underlying molecular mechanisms of endothelial function demonstrates a duality of reactive oxygen and nitrogen species in contributing to vascular homeostasis or leading to detrimental effects when formed in excess. Furthermore, changes in function and redox status of vascular smooth muscle cells contribute to age-related vascular remodeling. The age-dependent increase in free radical formation causes deterioration of the nitric oxide signaling cascade, alters and activates prostaglandin metabolism, and promotes novel oxidative posttranslational protein modifications that interfere with vascular and cell signaling pathways. As a result, vascular dysfunction manifests. Compensatory mechanisms are initially activated to cope with age-induced oxidative stress, but become futile, which results in irreversible oxidative modifications of biological macromolecules. These findings support the 'free radical theory of aging' but also show that reactive oxygen and nitrogen species are essential signaling molecules, regulating vascular homeostasis.

Reactive oxygen species as therapeutic targets in pulmonary hypertension

Pulmonary hypertension (PH) is characterized by a progressive elevation of pulmonary arterial pressure due to alterations of both pulmonary vascular structure and function. This disease is rare but life-threatening, leading to the development of right heart failure. Current PH treatments, designed to target altered pulmonary vascular reactivity, include vasodilating prostanoids, phosphodiesterase-5 inhibitors and endothelin-1 receptor antagonists. Although managing to slow the progression of the disease, these molecules still do not cure PH. More effective treatments need to be developed, and novel therapeutic strategies, targeting in particular vascular remodelling, are currently under investigation. Reactive oxygen species (ROS) are important physiological messengers in vascular cells. In addition to atherosclerosis and other systemic vascular diseases, emerging evidence also support a role of ROS in PH pathogenesis. ROS production is increased in animal models of PH, associated with NADPH oxidases increased expression, in particular of several Nox enzymes thought to be the major source of ROS in the pulmonary vasculature. These increases have also been observed in vitro and in vivo in humans. Moreover, several studies have shown either the deleterious effect of agents promoting ROS generation on pulmonary vasculature or, conversely, the beneficial effect of antioxidant agents in animal models of PH. In these studies, ROS production has been directly linked to pulmonary vascular remodelling, endothelial dysfunction, altered vasoconstrictive responses, inflammation and modifications of the extracellular matrix, all important features of PH pathophysiology. Altogether, these findings indicate that ROS are interesting therapeutic targets in PH. Blockade of ROS-dependent signalling pathways, or disruption of sources of ROS in the pulmonary vasculature, targeting in particular Nox enzymes, represent promising new therapeutic strategies in this disease.

Mechanism of reversal of high glucose-induced endothelial nitric oxide synthase uncoupling by tanshinone IIA in human endothelial cell line EA.hy926

Endothelial nitric oxide synthase (eNOS) uncoupling plays a causal role in endothelial dysfunction in many cardiovascular and metabolic diseases. Tanshinone IIA (Tan IIA), an active compound from Salvia miltiorrhiza, has been used to treat cardiovascular and metabolic diseases. However, the effects of Tan IIA on eNOS uncoupling have not been reported. We hypothesize that Tan IIA can regulate eNOS uncoupling in endothelium cells under oxidative stress. The results showed that eNOS-mediated NO generation was significantly decreased, accompanied by increased superoxide production and NOX4 expression. The ratio of eNOS dimer to monomer and NOS cofactor tetrahydrobiopterin (BH4) to 7,8-dihydrobiopterin (BH2) as well as expressions of heat-shock protein of 90kDa (HSP90), GTP cyclohydrolase-1 (GTPCH1) and dihydrofolate reductase (DHFR) were significantly decreased. Tan IIA significantly inhibited superoxide production and expression of NOX4, and increased NO generation and eNOS homodimerization, as well as expressions of HSP90, GTPCH1 and DHFR in a concentration-dependent manner. The ratio of BH4 to BH2 was also elevated by Tan IIA. In addition, Tan IIA significantly inhibited the increase in expression of PI3K in high glucose treated cells. Wortmannin, a PI3K inhibitor, significantly inhibited the high glucose induced NOX4 expression. The results demonstrated that Tan IIA restored eNOS uncoupling induced by high glucose by targeting NADPH oxidase, HSP90, GTPCH1 and DHFR, and PI3K pathway, which leads to reduced intracellular oxidative stress and increased NO generation. Tan IIA may be used as a prototype agent to restore eNOS coupling under certain cardiovascular and metabolic diseases.

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.

Zinc supplementation attenuates metallothionein and oxidative stress changes in kidney of streptozotocin-induced diabetic rats

Zinc is an element that under physiological conditions preferentially binds to and is a potent inducer of metallothionein under physiological conditions. The present study was conducted to explore whether zinc supplementation morphologically and biochemically protects against diabetic nephropathy through modulation of kidney metallothionein induction and oxidative stress in streptozotocin-induced diabetic rats. Thirty-two Wistar albino male rats were equally divided into four groups. The first group was used as untreated controls and the second group was supplemented with 30 mg/kg/day zinc as zinc sulfate. The third group was treated with streptozotocin to induce diabetes and the fourth group was treated with streptozotocin and supplemented with zinc as described for group 2. The blood glucose and micro-albuminuria levels, body and kidney weights were measured during the 42-day experimental period. At the end of the experiment, the kidneys were removed from all animals from the four groups. Diabetes resulted in degenerative kidney morphological changes. The metallothionein immunoreactivity level was lower and the kidney lipid peroxidation levels were higher in the diabetes group than in the controls. The metallothionein immunoreactivity levels were higher in the tubules of the zinc-supplemented diabetic rats as compared to the non-supplemented diabetic group. The zinc and metallothionein concentrations in kidney tissue were higher in the supplemented diabetic group compared to the non-supplemented diabetes group. The activity of glutathione peroxidase did not change in any of the four groups. In conclusion, the present study shows that zinc has a protective effect against diabetic damage of kidney tissue through stimulation of metallothionein synthesis and regulation of the oxidative stress.

Oxidant stress and skeletal muscle microvasculopathy in the metabolic syndrome

The evolution of the metabolic syndrome in afflicted individuals is, in part, characterized by the development of a severely pro-oxidant state within the vasculature. It has been previously demonstrated by many investigators that this increasingly pro-oxidant state can have severe negative implications for many relevant processes within the vasculature, including the coordination of dilator/constrictor tone or reactivity, the structural adaptations of the vascular wall or distal networks, as well as the integrated regulation of perfusion resistance across and throughout the vascular networks. The purpose of this review article is to present the different sources of oxidant stress within the setting of the metabolic syndrome, the available mechanism for attempts at regulation and the vascular outcomes associated with this condition. It is anticipated that this overview will help readers and investigators to more effectively design experiments and interpret their results within the extremely complicated setting of metabolic syndrome.

Zinc and regulation of inflammatory cytokines: implications for cardiometabolic disease

In atherosclerosis and diabetes mellitus, the concomitant presence of low-grade systemic inflammation and mild zinc deficiency highlights a role for zinc nutrition in the management of chronic disease. This review aims to evaluate the literature that reports on the interactions of zinc and cytokines. In humans, inflammatory cytokines have been shown both to up- and down-regulate the expression of specific cellular zinc transporters in response to an increased demand for zinc in inflammatory conditions. The acute phase response includes a rapid decline in the plasma zinc concentration as a result of the redistribution of zinc into cellular compartments. Zinc deficiency influences the generation of cytokines, including IL-1β, IL-2, IL-6, and TNF-α, and in response to zinc supplementation plasma cytokines exhibit a dose-dependent response. The mechanism of action may reflect the ability of zinc to either induce or inhibit the activation of NF-κB. Confounders in understanding the zinc-cytokine relationship on the basis of in vitro experimentation include methodological issues such as the cell type and the means of activating cells in culture. Impaired zinc homeostasis and chronic inflammation feature prominently in a number of cardiometabolic diseases. Given the high prevalence of zinc deficiency and chronic disease globally, the interplay of zinc and inflammation warrants further examination.

Ginsenoside Rb1 reverses H2O2-induced senescence in human umbilical endothelial cells: involvement of eNOS pathway

OBJECTIVE

Senescence of endothelial cells has been implicated in endothelial dysfunction and atherogenesis. This study investigated the effects of Rb1, a major ginsenoside in ginseng, on H2O2-induced senescence in primary human umbilical vein endothelial cells (HUVECs).

METHODS AND RESULTS

Real-time PCR and Western blot were used to detect the mRNA and protein expression, respectively. H2O2 (40∼100 μmol/L) effectively increased SA-β-gal activity and PAI-1 mRNA levels, two important senescence related biomarkers, in HUVECs, which were dramatically inhibited by Rb1 pre-incubation. Furthermore, Rb1 administration reversed the H2O2-decreased protein and mRNA levels of eNOS and its phosphorylation at Ser-1177, and the increased eNOS phosphorylation at Thr-495. As a result, Rb1 pretreatment restored the NO generation, as assayed by nitrate reductase method. However, pretreatment with L-NAME, a NOS inhibitor, abolished all the inhibitory effects of Rb1 on senescence. Importantly, Rb1 modulated the H2O2-altered caveolin-1 and pAkt, two most important regulators of eNOS expression and activity, in HUVECs.

CONCLUSIONS

We showed that Rb1 effectively protects HUVECs from senescence through eNOS modulation.

Ceramide mediates vascular dysfunction in diet-induced obesity by PP2A-mediated dephosphorylation of the eNOS-Akt complex

Vascular dysfunction that accompanies obesity and insulin resistance may be mediated by lipid metabolites. We sought to determine if vascular ceramide leads to arterial dysfunction and to elucidate the underlying mechanisms. Pharmacological inhibition of de novo ceramide synthesis, using the Ser palmitoyl transferase inhibitor myriocin, and heterozygous deletion of dihydroceramide desaturase prevented vascular dysfunction and hypertension in mice after high-fat feeding. These findings were recapitulated in isolated arteries in vitro, confirming that ceramide impairs endothelium-dependent vasorelaxation in a tissue-autonomous manner. Studies in endothelial cells reveal that de novo ceramide biosynthesis induced protein phosphatase 2A (PP2A) association directly with the endothelial nitric oxide synthase (eNOS)/Akt/Hsp90 complex that was concurrent with decreased basal and agonist-stimulated eNOS phosphorylation. PP2A attenuates eNOS phosphorylation by preventing phosphorylation of the pool of Akt that colocalizes with eNOS and by dephosphorylating eNOS. Ceramide decreased the association between PP2A and the predominantly cytosolic inhibitor 2 of PP2A. We conclude that ceramide mediates obesity-related vascular dysfunction by a mechanism that involves PP2A-mediated disruption of the eNOS/Akt/Hsp90 signaling complex. These results provide important insight into a pathway that represents a novel target for reversing obesity-related vascular dysfunction.

Dietary obesity increases NO and inhibits BKCa-mediated, endothelium-dependent dilation in rat cremaster muscle artery: association with caveolins and caveolae

Obesity is a risk factor for hypertension and other vascular disease. The aim of this study was to examine the effect of diet-induced obesity on endothelium-dependent dilation of rat cremaster muscle arterioles. Male Sprague-Dawley rats (213 ± 1 g) were fed a cafeteria-style high-fat or control diet for 16–20 wk. Control rats weighed 558 ± 7 g compared with obese rats 762 ± 12 g ( n = 52–56; P < 0.05). Diet-induced obesity had no effect on acetylcholine (ACh)-induced dilation of isolated, pressurized (70 mmHg) arterioles, but sodium nitroprusside (SNP)-induced vasodilation was enhanced. ACh-induced dilation of arterioles from control rats was abolished by a combination of the KCa blockers apamin, 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34), and iberiotoxin (IBTX; all 0.1 μmol/l), with no apparent role for nitric oxide (NO). In arterioles from obese rats, however, IBTX had no effect on responses to ACh while the NO synthase (NOS)/guanylate cyclase inhibitors Nω-nitro-l-arginine methyl ester (l-NAME; 100 μmol/l)/1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 μmol/l) partially inhibited ACh-induced dilation. Furthermore, NOS activity (but not endothelial NOS expression) was increased in arteries from obese rats. l-NAME/ODQ alone or removal of the endothelium constricted arterioles from obese but not control rats. Expression of caveolin-1 and -2 oligomers (but not monomers or caveolin-3) was increased in arterioles from obese rats. The number of caveolae was reduced in the endothelium of arteries, and caveolae density was increased at the ends of smooth muscle cells from obese rats. Diet-induced obesity abolished the contribution of large-conductance Ca2+-activated K+ channel to ACh-mediated endothelium-dependent dilation of rat cremaster muscle arterioles, while increasing NOS activity and inducing an NO-dependent component.

In utero exposure to benzo(a)pyrene predisposes offspring to cardiovascular dysfunction in later-life

In utero exposure of the fetus to benzo(a)pyrene [B(a)P], a polycyclic aromatic hydrocarbon, is thought to dysregulate cardiovascular development. To investigate the effects of in utero B(a)P exposure on cardiovascular development, timed-pregnant Long Evans Hooded (LEH) rats were exposed to diluent or B(a)P (150, 300, 600 and 1200 μg/kg/BW) by oral gavage on embryonic (E) days E14 (the metamorphosing embryo stage) through E17 (the 1st fetal stage). There were no significant effects of in utero exposure to B(a)P on the number of pups born per litter or in pre-weaning growth curves. Pre-weaning profiles for B(a)P metabolite generation from cardiovascular tissue were shown to be dose-dependent and elimination of these metabolites was shown to be time-dependent in exposed offspring. Systolic blood pressure on postnatal day P53 in the middle and high exposure groups of offspring were significantly elevated as compared to controls. Microarray and quantitative real-time PCR results were directly relevant to a biological process pathway in animal models for "regulation of blood pressure". Microarray and quantitative real-time PCR analysis revealed upregulation of mRNA expression for angiotensin (AngII), angiotensinogen (AGT) and endothelial nitric oxide synthase (eNOS) in exposed offspring. Biological network analysis and gene set enrichment analysis subsequently identified potential signaling mechanisms and molecular pathways that might explain the elevated systolic blood pressures observed in B(a)P-exposed offspring. Our findings suggest that in utero exposure to B(a)P predispose offspring to functional deficits in cardiovascular development that may contribute to cardiovascular dysfunction in later life.

Regulation of NAD(P)H oxidases by AMPK in cardiovascular systems

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are ubiquitously produced in cardiovascular systems. Under physiological conditions, ROS/RNS function as signaling molecules that are essential in maintaining cardiovascular function. Aberrant concentrations of ROS/RNS have been demonstrated in cardiovascular diseases owing to increased production or decreased scavenging, which have been considered common pathways for the initiation and progression of cardiovascular diseases such as atherosclerosis, hypertension, (re)stenosis, and congestive heart failure. NAD(P)H oxidases are primary sources of ROS and can be induced or activated by all known cardiovascular risk factors. Stresses, hormones, vasoactive agents, and cytokines via different signaling cascades control the expression and activity of these enzymes and of their regulatory subunits. But the molecular mechanisms by which NAD(P)H oxidase is regulated in cardiovascular systems remain poorly characterized. Investigations by us and others suggest that adenosine monophosphate-activated protein kinase (AMPK), as an energy sensor and modulator, is highly sensitive to ROS/RNS. We have also obtained convincing evidence that AMPK is a physiological suppressor of NAD(P)H oxidase in multiple cardiovascular cell systems. In this review, we summarize our current understanding of how AMPK functions as a physiological repressor of NAD(P)H oxidase.

Hyperglycemia and oxidative stress in cultured endothelial cells--a comparison of primary endothelial cells with an immortalized endothelial cell line

Diabetes mellitus is a major risk factor for the development of cardiovascular disease and oxidative stress plays an important role in this process. Therefore, we investigated the effects of hyperglycemia on the formation of reactive oxygen species (ROS) and nitric oxide/cGMP signaling in two different endothelial cell cultures. Human umbilical vein endothelial cells (HUVEC) and EA.hy 926 cells showed increased oxidative stress and impaired NO-cGMP signaling in response to hyperglycemia. The major difference between the two different cell types was the dramatic decrease in viability in HUVEC whereas EA.hy cells showed rather increased growth under hyperglycemic conditions. Starvation led to an additional substantial decrease in viability and increased superoxide formation in HUVEC. Both endothelial cell types, HUVEC and EA.hy 926, may be used as models for vascular hyperglycemia. However, high growth medium should be used to avoid starvation-induced oxidative stress and cell death.

AMP-activated protein kinase, stress responses and cardiovascular diseases

AMPK (AMP-activated protein kinase) is one of the key players in maintaining intracellular homoeostasis. AMPK is well known as an energy sensor and can be activated by increased intracellular AMP levels. Generally, the activation of AMPK turns on catabolic pathways that generate ATP, while inhibiting cell proliferation and biosynthetic processes that consume ATP. In recent years, intensive investigations on the regulation and the function of AMPK indicates that AMPK not only functions as an intracellular energy sensor and regulator, but is also a general stress sensor that is important in maintaining intracellular homoeostasis during many kinds of stress challenges. In the present paper, we will review recent literature showing that AMPK functions far beyond its proposed energy sensor and regulator function. AMPK regulates ROS (reactive oxygen species)/redox balance, autophagy, cell proliferation, cell apoptosis, cellular polarity, mitochondrial function and genotoxic response, either directly or indirectly via numerous downstream pathways under physiological and pathological conditions.

Mechanistic overview of reactive species-induced degradation of the endothelial glycocalyx during hepatic ischemia/reperfusion injury

Endothelial cells are covered by a delicate meshwork of glycoproteins known as the glycocalyx. Under normophysiological conditions the glycocalyx plays an active role in maintaining vascular homeostasis by deterring primary and secondary hemostasis and leukocyte adhesion and by regulating vascular permeability and tone. During (micro)vascular oxidative and nitrosative stress, which prevails in numerous metabolic (diabetes), vascular (atherosclerosis, hypertension), and surgical (ischemia/reperfusion injury, trauma) disease states, the glycocalyx is oxidatively and nitrosatively modified and degraded, which culminates in an exacerbation of the underlying pathology. Consequently, glycocalyx degradation due to oxidative/nitrosative stress has far-reaching clinical implications. In this review the molecular mechanisms of reactive oxygen and nitrogen species-induced destruction of the endothelial glycocalyx are addressed in the context of hepatic ischemia/reperfusion injury as a model disease state. Specifically, the review focuses on (i) the mechanisms of glycocalyx degradation during hepatic ischemia/reperfusion, (ii) the molecular and cellular players involved in the degradation process, and (iii) its implications for hepatic pathophysiology. These topics are projected against a background of liver anatomy, glycocalyx function and structure, and the biology/biochemistry and the sources/targets of reactive oxygen and nitrogen species. The majority of the glycocalyx-related mechanisms elucidated for hepatic ischemia/reperfusion are extrapolatable to the other aforementioned disease states.

Emerging role of PKA/eNOS pathway in therapeutic angiogenesis for ischaemic tissue diseases

Although an abundant amount of research has been devoted to the study of angiogenesis, its precise mechanisms are incompletely understood. Numerous clinical trials focused on therapeutic angiogenesis for the treatment of tissue ischaemia have not been as successful as those of preclinical studies. Thus, additional studies are needed to better understand critical molecular mechanisms regulating ischaemic neovascularization to identify novel therapeutic agents. Nitric oxide (NO) plays a central role in ischaemic neovascularization through the generation of cyclic guanosine monophosphate (cGMP) and the activation of several other signalling responses. Accumulated evidence suggests that endothelial protein kinase A/endothelial NO synthase (PKA/eNOS) signalling may play an important role in ischaemic disorders by promoting neovascularization. This review highlights recent advances in the role of the PKA/eNOS and NO-cGMP-kinase cascade pathway in ischaemic neovascularization. We also discuss molecular relationships of PKA/eNOS with other angiogenic pathways and explore the possibility of activation of the NO/nitrite endocrine system as potential therapeutic targets for ischaemic angiogenesis.

Role of oxidative stress in diabetes-mediated vascular dysfunction: unifying hypothesis of diabetes revisited

Oxidative stress is recognized as a key participant in the development of diabetic complications in the vasculature. One of the seminal studies advancing the role of oxidative stress in vascular endothelial cells proposed that oxidative stress-mediated diversion of glycolytic intermediates into pathological pathways was a key underlying element in the development of diabetic complications. It is widely recognized that flux through glycolysis slows during diabetes. However, several bottlenecks develop in the glycolytic pathway, including glucose transport, phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase and pyruvate kinase. Of these limiting steps in glycolysis, glyceraldehyde-3-phosphate dehydrogenase is most sensitive to oxidative stress, leading to the hypothesis that glyceraldehyde-3-phosphate inactivation by ribosylation underlies the diversion of glycolytic intermediates into pathological pathways. However, recent studies question the mechanism underlying the effect of reactive oxygen species on key enzymes of the glycolytic pathway. The present review critiques the major premises of the hypothesis and concludes that further study of the role of oxidative stress in the development of diabetes-mediated vasculature dysfunction is warranted.

Endothelium-mediated control of vascular tone: COX-1 and COX-2 products

Endothelium-dependent contractions contribute to endothelial dysfunction in various animal models of aging, diabetes and cardiovascular diseases. In the spontaneously hypertensive rat, the archetypal model for endothelium-dependent contractions, the production of the endothelium-derived contractile factors (EDCF) involves an increase in endothelial intracellular calcium concentration, the production of reactive oxygen species, the predominant activation of cyclooxygenase-1 (COX-1) and to a lesser extent that of COX-2, the diffusion of EDCF towards the smooth muscle cells and the subsequent stimulation of their thromboxane A2-endoperoxide TP receptors. Endothelium-dependent contractions are also observed in various models of hypertension, aging and diabetes. They generally also involve the generation of COX-1- and/or COX-2-derived products and the activation of smooth muscle TP receptors. Depending on the model, thromboxane A(2), PGH(2), PGF(2α), PGE(2) and paradoxically PGI(2) can all act as EDCFs. In human, the production of COX-derived EDCF is a characteristic of the aging and diseased blood vessels, with essential hypertension causing an earlier onset and an acceleration of this endothelial dysfunction. As it has been observed in animal models, COX-1, COX-2 or both isoforms can contribute to these endothelial dysfunctions. Since in most cases, the activation of TP receptors is the common downstream effector, selective antagonists of this receptor should curtail endothelial dysfunction and be of therapeutic interest in the treatment of cardiovascular disorders.