Discovering a Reliable Heat-Shock Factor-1 Inhibitor to Treat Human Cancers: Potential Opportunity for Phytochemists

Heat-shock factor-1 (HSF-1) is an important transcription factor that regulates pathogenesis of many human diseases through its extensive transcriptional regulation. Especially, it shows pleiotropic effects in human cancer, and hence it has recently received increased attention of cancer researchers. After myriad investigations on HSF-1, the field has advanced to the phase where there is consensus that finding a potent and selective pharmacological inhibitor for this transcription factor will be a major break-through in the treatment of various human cancers. Presently, all reported inhibitors have their limitations, made evident at different stages of clinical trials. This brief account summarizes the advances with tested natural products as HSF-1 inhibitors and highlights the necessity of phytochemistry in this endeavor of discovering a potent pharmacological HSF-1 inhibitor.

Heat shock factor-1 knockout enhances cholesterol 7α-hydroxylase (CYP7A1) and multidrug transporter (MDR1) gene expressions to attenuate atherosclerosis

AIMS

Stress response, in terms of activation of stress factors, is known to cause obesity and coronary heart disease such as atherosclerosis in human. However, the underlying mechanism(s) of these pathways are not known. Here, we investigated the effect of heat shock factor-1 (HSF-1) on atherosclerosis.

METHODS AND RESULTS

HSF-1 and low-density lipoprotein receptor (LDLr) double knockout (HSF-1(-/-)/LDLr(-/-)) and LDLr knockout (LDLr(-/-)) mice were fed with atherogenic western diet (WD) for 12 weeks. WD-induced weight gain and atherosclerotic lesion in aortic arch and carotid regions were reduced in HSF-1(-/-)/LDLr(-/-) mice, compared with LDLr(-/-) mice. Also, repression of PPAR-γ2 and AMPKα expression in adipose tissue, low hepatic steatosis, and lessened plasma adiponectins and lipoproteins were observed. In HSF-1(-/-)/LDLr(-/-) liver, higher cholesterol 7α-hydroxylase (CYP7A1) and multidrug transporter [MDR1/P-glycoprotein (P-gp)] gene expressions were observed, consistent with higher bile acid transport and larger hepatic bile ducts. Luciferase reporter gene assays with wild-type CYP7A1 and MDR1 promoters showed lesser luminescence than with mutant promoters (HSF-1 binding site deleted), indicating that HSF-1 binding is repressive of CYP7A1 and MDR1 gene expressions.

CONCLUSION

HSF-1 ablation not only eliminates heat shock response, but it also transcriptionally up-regulates CYP7A1 and MDR1/P-gp axis in WD-diet fed HSF-1(-/-)/LDLr(-/-) mice to reduce atherosclerosis.

Sulfite Oxidase Activity of Cytochrome c: Role of Hydrogen Peroxide

In humans, sulfite is generated endogenously by the metabolism of sulfur containing amino acids such as methionine and cysteine. Sulfite is also formed from exposure to sulfur dioxide, one of the major environmental pollutants. Sulfite is used as an antioxidant and preservative in dried fruits, vegetables, and beverages such as wine. Sulfite is also used as a stabilizer in many drugs. Sulfite toxicity has been associated with allergic reactions characterized by sulfite sensitivity, asthma, and anaphylactic shock. Sulfite is also toxic to neurons and cardiovascular cells. Recent studies suggest that the cytotoxicity of sulfite is mediated by free radicals; however, molecular mechanisms involved in sulfite toxicity are not fully understood. Cytochrome c (cyt c) is known to participate in mitochondrial respiration and has antioxidant and peroxidase activities. Studies were performed to understand the related mechanism of oxidation of sulfite and radical generation by ferric cytochrome c (Fe³⁺cyt c) in the absence and presence of H₂O₂. Electron paramagnetic resonance (EPR) spin trapping studies using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) were performed with sulfite, Fe³⁺cyt c, and H₂O₂. An EPR spectrum corresponding to the sulfite radical adducts of DMPO (DMPO-SO₃^-) was obtained. The amount of DMPO-SO3- formed from the oxidation of sulfite by the Fe³⁺cyt c increased with sulfite concentration. In addition, the amount of DMPO-SO3- formed by the peroxidase activity of Fe³⁺cyt c also increased with sulfite and H₂O₂ concentration. From these results, we propose a mechanism in which the Fe³⁺cyt c and its peroxidase activity oxidizes sulfite to sulfite radical. Our results suggest that Fe³⁺cyt c could have a novel role in the deleterious effects of sulfite in biological systems due to increased production of sulfite radical. It also shows that the increased production of sulfite radical may be responsible for neurotoxicity and some of the injuries which occur to humans born with molybdenum cofactor and sulfite oxidase deficiencies.

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Cytochrome c oxidizes sulfite to sulfite radical.

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In the presence of H₂O₂, sulfite radical generation from cyt c increases.

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The formation of sulfite radical is sulfite concentration dependent.

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This mechanism of sulfite radical formation may be important in sulfite toxicity.

Reversal of SIN-1-induced eNOS dysfunction by the spin trap, DMPO, in bovine aortic endothelial cells via eNOS phosphorylation

BACKGROUND AND PURPOSE

Nitric oxide (NO) derived from eNOS is mostly responsible for the maintenance of vascular homeostasis and its decreased bioavailability is characteristic of reactive oxygen species (ROS)-induced endothelial dysfunction (ED). Because 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), a commonly used spin trap, can control intracellular nitroso-redox balance by scavenging ROS and donating NO, it was employed as a cardioprotective agent against ED but the mechanism of its protection is still not clear. This study elucidated the mechanism of protection by DMPO against SIN-1-induced oxidative injury to bovine aortic endothelial cells (BAEC).

EXPERIMENTAL APPROACH

BAEC were treated with SIN-1, as a source of peroxynitrite anion (ONOO⁻), and then incubated with DMPO. Cytotoxicity following SIN-1 alone and cytoprotection by adding DMPO was assessed by MTT assay. Levels of ROS and NO generation from HEK293 cells transfected with wild-type and mutant eNOS cDNAs, tetrahydrobiopterin bioavailability, eNOS activity, eNOS and Akt kinase phosphorylation were measured.

KEY RESULTS

Post-treatment of cells with DMPO attenuated SIN-1-mediated cytotoxicity and ROS generation, restoration of NO levels via increased in eNOS activity and phospho-eNOS levels. Treatment with DMPO alone significantly increased NO levels and induced phosphorylation of eNOS Ser¹¹⁷⁹ via Akt kinase. Transfection studies with wild-type and mutant human eNOS confirmed the dual role of eNOS as a producer of superoxide anion (O₂⁻) with SIN-1 treatment, and a producer of NO in the presence of DMPO.

CONCLUSION AND IMPLICATIONS

Post-treatment with DMPO of oxidatively challenged cells reversed eNOS dysfunction and could have pharmacological implications in the treatment of cardiovascular diseases.

Developing an irreversible inhibitor of human DDAH-1, an enzyme upregulated in melanoma

Inhibitors of the human enzyme dimethylarginine dimethylaminohydrolase-1 (DDAH-1) can raise endogenous levels of asymmetric dimethylarginine (ADMA) and lead to a subsequent inhibition of nitric oxide synthesis. In this study, N(5) -(1-imino-2-chloroethyl)-L-ornithine (Cl-NIO) is shown to be a potent time- and concentration-dependent inhibitor of purified human DDAH-1 (KI =1.3±0.6 μM; kinact =0.34±0.07 min(-1) ), with >500-fold selectivity against two arginine-handling enzymes in the same pathway. An activity probe is used to measure the "in cell" IC50 value (6.6±0.2 μM) for Cl-NIO inhibition of DDAH-1 artificially expressed within cultured HEK293T cells. A screen of diverse melanoma cell lines reveals that a striking 50/64 (78 %) of melanoma lines tested showed increased levels of DDAH-1 relative to normal melanocyte control lines. Treatment of the melanoma A375 cell line with Cl-NIO shows a subsequent decrease in cellular nitric oxide production. Cl-NIO is a promising tool for the study of methylarginine-mediated nitric oxide control and a potential therapeutic lead compound for other indications with elevated nitric oxide production, such as septic shock and idiopathic pulmonary fibrosis.

Diminazene attenuates pulmonary hypertension and improves angiogenic progenitor cell functions in experimental models

RATIONALE

Studies have demonstrated that angiotensin-converting enzyme 2 (ACE2) plays a protective role against lung diseases, including pulmonary hypertension (PH). Recently, an antitrypanosomal drug, diminazene aceturate (DIZE), was shown to exert an "off-target" effect of enhancing the enzymatic activity of ACE2 in vitro.

OBJECTIVES

To evaluate the pharmacological actions of DIZE in experimental models of PH.

METHODS

PH was induced in male Sprague Dawley rats by monocrotaline, hypoxia, or bleomycin challenge. Subsets of animals were simultaneously treated with DIZE. In a separate set of experiments, DIZE was administered after 3 weeks of PH induction to determine whether the drug could reverse PH.

MEASUREMENTS AND MAIN RESULTS

DIZE treatment significantly prevented the development of PH in all of the animal models studied. The protective effects were associated with an increase in the vasoprotective axis of the lung renin-angiotensin system, decreased inflammatory cytokines, improved pulmonary vasoreactivity, and enhanced cardiac function. These beneficial effects were abolished by C-16, an ACE2 inhibitor. Initiation of DIZE treatment after the induction of PH arrested disease progression. Endothelial dysfunction represents a hallmark of PH pathophysiology, and growing evidence suggests that bone marrow-derived angiogenic progenitor cells contribute to endothelial homeostasis. We observed that angiogenic progenitor cells derived from the bone marrow of monocrotaline-challenged rats were dysfunctional and were repaired by DIZE treatment. Likewise, angiogenic progenitor cells isolated from patients with PH exhibited diminished migratory capacity toward the key chemoattractant stromal-derived factor 1α, which was corrected by in vitro DIZE treatment.

CONCLUSIONS

Our results identify a therapeutic potential of DIZE in PH therapy.

Hyperoxia and transforming growth factor β1 signaling in the post-ischemic mouse heart

AIMS

Following ischemic injury, myocardial healing and remodeling occur with characteristic myofibroblast trans-differentiation and scar formation. The current study tests the hypothesis that hyperoxia and nitric oxide (NO) regulate TGF-β1 signaling in the post-ischemic myocardium.

MAIN METHODS

C57BL/6 wild-type (WT), endothelial and inducible nitric oxide synthase knockout (eNOS(-/-) and iNOS(-/-)) mice were subjected to 30-min left anterior descending coronary artery occlusion followed by reperfusion. Myocardial tissue oxygenation was monitored with electron paramagnetic resonance oximetry. Protein expressions of TGF-β1, receptor-activated small mothers against decapentaplegic homolog (Smad), p21 and α-smooth muscle actin (α-SMA) were measured with enzyme-linked immunosorbent assay (ELISA), Western immunoblotting, and immunohistochemical staining.

KEY FINDINGS

There was a hyperoxic state in the post-ischemic myocardial tissue. Protein expressions of total and active TGF-β1, p-Smad2/3 over t-Smad2/3 ratio, p21, and α-SMA were significantly increased in WT mice compared to Sham control. Knockout of eNOS or iNOS further increased protein expression of these signals. The expression of α-SMA was more abundant in the infarct of eNOS(-/-) and iNOS(-/-) mice than WT mice. A protein band indicating nitration of TGF-β type-II receptor (TGFβRII) was observed from WT heart. Carbogen (95% O2 plus 5% CO2) treatment increased the ratio of p-Smad2/t-Smad2, which was inhibited by 10006329 EUK (EUK134) and sodium nitroprusside (SNP). In conclusion, hyperoxia up-regulated and NO/ONOO(-) inhibited cardiac TGF-β1 signaling and myofibroblast trans-differentiation.

SIGNIFICANCE

These findings may provide new insights in myocardial infarct healing and repair.

Age and exercise training alter signaling through reactive oxygen species in the endothelium of skeletal muscle arterioles

Exercise training ameliorates age-related impairments in endothelium-dependent vasodilation in skeletal muscle arterioles. Additionally, exercise training is associated with increased superoxide production. The purpose of this study was to determine the role of superoxide and superoxide-derived reactive oxygen species (ROS) signaling in mediating endothelium-dependent vasodilation of soleus muscle resistance arterioles from young and old, sedentary and exercise-trained rats. Young (3 mo) and old (22 mo) male rats were either exercise trained or remained sedentary for 10 wk. To determine the impact of ROS signaling on endothelium-dependent vasodilation, responses to acetylcholine were studied under control conditions and during the scavenging of superoxide and/or hydrogen peroxide. To determine the impact of NADPH oxidase-derived ROS, endothelium-dependent vasodilation was determined following NADPH oxidase inhibition. Reactivity to superoxide and hydrogen peroxide was also determined. Tempol, a scavenger of superoxide, and inhibitors of NADPH oxidase reduced endothelium-dependent vasodilation in all groups. Similarly, treatment with catalase and simultaneous treatment with tempol and catalase reduced endothelium-dependent vasodilation in all groups. Decomposition of peroxynitrite also reduced endothelium-dependent vasodilation. Aging had no effect on arteriolar protein content of SOD-1, catalase, or glutathione peroxidase-1; however, exercise training increased protein content of SOD-1 in young and old rats, catalase in young rats, and glutathione peroxidase-1 in old rats. These data indicate that ROS signaling is necessary for endothelium-dependent vasodilation in soleus muscle arterioles, and that exercise training-induced enhancement of endothelial function occurs, in part, through an increase in ROS signaling.

Nitric oxide synthases and atrial fibrillation

Oxidative stress has been implicated in the pathogenesis of atrial fibrillation. There are multiple systems in the myocardium which contribute to redox homeostasis, and loss of homeostasis can result in oxidative stress. Potential sources of oxidants include nitric oxide synthases (NOS), which normally produce nitric oxide in the heart. Two NOS isoforms (1 and 3) are normally expressed in the heart. During pathologies such as heart failure, there is induction of NOS 2 in multiple cell types in the myocardium. In certain conditions, the NOS enzymes may become uncoupled, shifting from production of nitric oxide to superoxide anion, a potent free radical and oxidant. Multiple lines of evidence suggest a role for NOS in the pathogenesis of atrial fibrillation. Therapeutic approaches to reduce atrial fibrillation by modulation of NOS activity may be beneficial, although further investigation of this strategy is needed.

Hydrogen sulfide increases nitric oxide production from endothelial cells by an akt-dependent mechanism

Hydrogen sulfide (H₂S) and nitric oxide (NO) are both gasotransmitters that can elicit synergistic vasodilatory responses in the in the cardiovascular system, but the mechanisms behind this synergy are unclear. In the current study we investigated the molecular mechanisms through which H₂S regulates endothelial NO production. Initial studies were performed to establish the temporal and dose-dependent effects of H₂S on NO generation using EPR spin trapping techniques. H₂S stimulated a twofold increase in NO production from endothelial nitric oxide synthase (eNOS), which was maximal 30 min after exposure to 25–150 μM H₂S. Following 30 min H₂S exposure, eNOS phosphorylation at Ser 1177 was significantly increased compared to control, consistent with eNOS activation. Pharmacological inhibition of Akt, the kinase responsible for Ser 1177 phosphorylation, attenuated the stimulatory effect of H₂S on NO production. Taken together, these data demonstrate that H₂S up-regulates NO production from eNOS through an Akt-dependent mechanism. These results implicate H₂S in the regulation of NO production in endothelial cells, and suggest that deficiencies in H₂S signaling can directly impact processes regulated by NO.

Effects of high adherence to mediterranean or low-fat diets in medicated secondary prevention patients

Although the Mediterranean diet (MD) and the low-fat Therapeutic Lifestyle Changes Diet (TLCD) promote equivalent increases in event-free survival in secondary coronary prevention, possible mechanisms of such complete dietary patterns in these patients, usually medicated, are unclear. The aim of this study was to investigate the effects of the MD versus the TLCD in markers of endothelial function, oxidative stress, and inflammation after acute coronary syndromes. Comparison was made between 3 months of the MD (n = 21; rich in whole grains, vegetables, fruits, nuts, and olive oil, plus red wine) and the TLCD (n = 19; plus phytosterols 2 g/day) in a highly homogenous population of stable patients who experienced coronary events in the previous 2 years (aged 45 to 65 years, all men) allocated to each diet under a strategy designed to optimize adherence, documented as >90%. Baseline demographics, body mass index and clinical data, and use of statins and other drugs were similar between groups. The MD and TLCD promoted similar decreases in body mass index and blood pressure (p ≤0.001) and particularly in plasma asymmetric dimethylarginine levels (p = 0.02) and l-arginine/asymmetric dimethylarginine ratios (p = 0.01). The 2 diets did not further enhance flow-mediated brachial artery dilation compared to baseline (4.4 ± 4.0%). Compared to the TLCD, the MD promoted decreases in blood leukocyte count (p = 0.025) and increases in high-density lipoprotein levels (p = 0.053) and baseline brachial artery diameter. Compared to the MD, the TLCD decreased low-density lipoprotein and oxidized low-density lipoprotein plasma levels, although the ratio of oxidized to total low-density lipoprotein remained unaltered. Glucose, high-sensitivity C-reactive protein, triglycerides, myeloperoxidase, intercellular adhesion molecular, vascular cell adhesion molecule, and glutathione serum and plasma levels remained unchanged with either diet. In conclusion, medicated secondary prevention patients show evident although small responses to the MD and the TLCD, with improved markers of redox homeostasis and metabolic effects potentially related to atheroprotection.

Suppression of eNOS-derived superoxide by caveolin-1: a biopterin-dependent mechanism

In the vasculature, nitric oxide (NO) is generated by endothelial NO synthase (eNOS) in a calcium/calmodulin-dependent reaction. In the absence of the requisite eNOS cofactor tetrahydrobiopterin (BH(4)), NADPH oxidation is uncoupled from NO generation, leading to the production of superoxide. Although this phenomenon is apparent with purified enzyme, cellular studies suggest that formation of the BH(4) oxidation product, dihydrobiopterin, is the molecular trigger for eNOS uncoupling rather than BH(4) depletion alone. In the current study, we investigated the effects of both BH(4) depletion and oxidation on eNOS-derived superoxide production in endothelial cells in an attempt to elucidate the molecular mechanisms regulating eNOS oxidase activity. Results demonstrated that pharmacological depletion of endothelial BH(4) does not result in eNOS oxidase activity, whereas BH(4) oxidation gave rise to significant eNOS-oxidase activity. These findings suggest that the endothelium possesses regulatory mechanisms, which prevent eNOS oxidase activity from pterin-free eNOS. Using a combination of gene silencing and pharmacological approaches, we demonstrate that eNOS-caveolin-1 association is increased under conditions of reduced pterin bioavailability and that this sequestration serves to suppress eNOS uncoupling. Using small interfering RNA approaches, we demonstrate that caveolin-1 gene silencing increases eNOS oxidase activity to 85% of that observed under conditions of BH(4) oxidation. Moreover, when caveolin-1 silencing was combined with a pharmacological inhibitor of AKT, BH(4) depletion increased eNOS-derived superoxide to 165% of that observed with BH(4) oxidation. This study identifies a critical role of caveolin-1 in the regulation of eNOS uncoupling and provides new insight into the mechanisms through which disease-associated changes in caveolin-1 expression may contribute to endothelial dysfunction.

Cell death induced by the Jak2 inhibitor, G6, correlates with cleavage of vimentin filaments

Hyperkinetic Jak2 tyrosine kinase signaling has been implicated in several human diseases including leukemia, lymphoma, myeloma, and the myeloproliferative neoplasms. Using structure-based virtual screening, we previously identified a novel Jak2 inhibitor named G6. We showed that G6 specifically inhibits Jak2 kinase activity and suppresses Jak2-mediated cellular proliferation. To elucidate the molecular and biochemical mechanisms by which G6 inhibits Jak2-mediated cellular proliferation, we treated Jak2-V617F expressing human erythroleukemia (HEL) cells for 12 h with either vehicle control or 25 μM of the drug and compared protein expression profiles using two-dimensional gel electrophoresis. One differentially expressed protein identified by electrospray mass spectroscopy was the intermediate filament protein, vimentin. It was present in DMSO treated cells but absent in G6 treated cells. HEL cells treated with G6 showed both time- and dose-dependent cleavage of vimentin as well as a marked reorganization of vimentin intermediate filaments within intact cells. In a mouse model of Jak2-V617F mediated human erythroleukemia, G6 also decreased the levels of vimentin protein, in vivo. The G6-induced cleavage of vimentin was found to be Jak2-dependent and calpain-mediated. Furthermore, we found that intracellular calcium mobilization is essential and sufficient for the cleavage of vimentin. Finally, we show that the cleavage of vimentin intermediate filaments, per se, is sufficient to reduce HEL cell viability. Collectively, these results suggest that G6-induced inhibition of Jak2-mediated pathogenic cell growth is concomitant with the disruption of intracellular vimentin filaments. As such, this work describes a novel pathway for the targeting of Jak2-mediated pathological cell growth.

Suppression of eNOS-derived superoxide by caveolin-1: a biopterin-dependent mechanism

In the vasculature, nitric oxide (NO) is generated by endothelial NO synthase (eNOS) in a calcium/calmodulin-dependent reaction. In the absence of the requisite eNOS cofactor tetrahydrobiopterin (BH(4)), NADPH oxidation is uncoupled from NO generation, leading to the production of superoxide. Although this phenomenon is apparent with purified enzyme, cellular studies suggest that formation of the BH(4) oxidation product, dihydrobiopterin, is the molecular trigger for eNOS uncoupling rather than BH(4) depletion alone. In the current study, we investigated the effects of both BH(4) depletion and oxidation on eNOS-derived superoxide production in endothelial cells in an attempt to elucidate the molecular mechanisms regulating eNOS oxidase activity. Results demonstrated that pharmacological depletion of endothelial BH(4) does not result in eNOS oxidase activity, whereas BH(4) oxidation gave rise to significant eNOS-oxidase activity. These findings suggest that the endothelium possesses regulatory mechanisms, which prevent eNOS oxidase activity from pterin-free eNOS. Using a combination of gene silencing and pharmacological approaches, we demonstrate that eNOS-caveolin-1 association is increased under conditions of reduced pterin bioavailability and that this sequestration serves to suppress eNOS uncoupling. Using small interfering RNA approaches, we demonstrate that caveolin-1 gene silencing increases eNOS oxidase activity to 85% of that observed under conditions of BH(4) oxidation. Moreover, when caveolin-1 silencing was combined with a pharmacological inhibitor of AKT, BH(4) depletion increased eNOS-derived superoxide to 165% of that observed with BH(4) oxidation. This study identifies a critical role of caveolin-1 in the regulation of eNOS uncoupling and provides new insight into the mechanisms through which disease-associated changes in caveolin-1 expression may contribute to endothelial dysfunction.

Tetrahydrobiopterin depletion and NOS2 uncoupling contribute to heart failure-induced alterations in atrial electrophysiology

AIMS

Heart failure is a common antecedent to atrial fibrillation; both heart failure and atrial fibrillation are associated with increased myocardial oxidative stress. Chronic canine heart failure reduces atrial action potential duration and atrial refractoriness. We hypothesized that inducible nitric oxide synthase 2 (NOS2) contributes to atrial oxidative stress and electrophysiologic alterations.

METHODS AND RESULTS

A 16-week canine tachypacing model of heart failure was used (n= 21). At 10 weeks, dogs were randomized to either placebo (n = 12) or active treatment (n = 9) with NOS cofactor, tetrahydrobiopterin (BH(4), 50 mg), and NOS substrate (L-arginine, 3 g) twice daily for 6 weeks. A group of matched controls (n = 7) was used for comparison. Heart failure increased atrial NOS2 and reduced atrial BH(4), while L-arginine was unchanged. Treatment reduced inducible atrial fibrillation and normalized the heart failure-induced shortening of the left atrial myocyte action potential duration. Treatment increased atrial [BH(4)] while [L-arginine] was unchanged. Treatment did not improve left ventricular function or dimensions. Heart failure-induced reductions in atrial [BH(4)] resulted in NOS uncoupling, as measured by NO and superoxide anion (O(2)(·-)) production, while BH(4) and L-arginine treatment normalized NO and O(2)(·-). Heart failure resulted in left atrial oxidative stress, which was attenuated by BH(4) and L-arginine treatment.

CONCLUSION

Chronic non-ischaemic heart failure results in atrial oxidative stress and electrophysiologic abnormalities by depletion of BH(4) and uncoupling of NOS2. Modulation of NOS2 activity by repletion of BH(4) may be a safe and effective approach to reduce the frequency of atrial arrhythmias during heart failure.

Suppression of eNOS-derived superoxide by caveolin-1: a biopterin-dependent mechanism

In the vasculature, nitric oxide (NO) is generated by endothelial NO synthase (eNOS) in a calcium/calmodulin-dependent reaction. In the absence of the requisite eNOS cofactor tetrahydrobiopterin (BH(4)), NADPH oxidation is uncoupled from NO generation, leading to the production of superoxide. Although this phenomenon is apparent with purified enzyme, cellular studies suggest that formation of the BH(4) oxidation product, dihydrobiopterin, is the molecular trigger for eNOS uncoupling rather than BH(4) depletion alone. In the current study, we investigated the effects of both BH(4) depletion and oxidation on eNOS-derived superoxide production in endothelial cells in an attempt to elucidate the molecular mechanisms regulating eNOS oxidase activity. Results demonstrated that pharmacological depletion of endothelial BH(4) does not result in eNOS oxidase activity, whereas BH(4) oxidation gave rise to significant eNOS-oxidase activity. These findings suggest that the endothelium possesses regulatory mechanisms, which prevent eNOS oxidase activity from pterin-free eNOS. Using a combination of gene silencing and pharmacological approaches, we demonstrate that eNOS-caveolin-1 association is increased under conditions of reduced pterin bioavailability and that this sequestration serves to suppress eNOS uncoupling. Using small interfering RNA approaches, we demonstrate that caveolin-1 gene silencing increases eNOS oxidase activity to 85% of that observed under conditions of BH(4) oxidation. Moreover, when caveolin-1 silencing was combined with a pharmacological inhibitor of AKT, BH(4) depletion increased eNOS-derived superoxide to 165% of that observed with BH(4) oxidation. This study identifies a critical role of caveolin-1 in the regulation of eNOS uncoupling and provides new insight into the mechanisms through which disease-associated changes in caveolin-1 expression may contribute to endothelial dysfunction.

Abstract 5127: G6-mediated inhibition of Jak2 tyrosine kinase correlates with the cleavage and cellular reorganization of vimentin

Hyperkinetic Jak2 tyrosine kinase signaling has been implicated in several human diseases including various leukemias, lymphomas, myelomas and the myeloproliferative neoplasms. Using structure-based virtual screening, our lab previously identified a novel Jak2 inhibitor named G6. We showed that G6 has a specific inhibitory effect on Jak2 tyrosine kinase activity and potently suppresses Jak2-mediated cellular proliferation. To elucidate the biochemical and cellular mechanisms by which G6 inhibits Jak2-mediated cell proliferation, we treated Jak2-V617F expressing human erythroleukemia (HEL) cells for 12 hours with either vehicle control (DMSO) or 25 µM of the drug and then compared their protein expression profiles using two-dimensional gel electrophoresis. One protein that was found to be differentially expressed was the intermediate filament protein vimentin. Specifically, we found that full length vimentin was robustly expressed in untreated cells and absent in G6 treated cells. We hypothesized that inhibition of Jak2-V617F dependent pathogenic cell growth by G6 correlates with the cleavage and cellular reorganization of intermediate vimentin filaments. To this end, we found that the treatment of HEL cells with G6 induced a time- and dose-dependent cleavage of vimentin. This G6-induced cleavage of vimentin was both Jak2-dependent and calpain-mediated. Using indirect immunofluorescence, we found that G6 treatment resulted in a marked reorganization of vimentin filaments within cells. Finally, using a mouse model of Jak2-V617F mediated neoplasia, we found that G6 decreased the levels of vimentin protein within the bone marrow of G6 treated mice when compared to animals that received vehicle control. Overall, these results demonstrate that G6-mediated inhibition of Jak2-dependent pathogenic cell growth correlates with the proteolytic cleavage of full length vimentin and the reorganization of intermediate vimentin filaments within cells. As such, we may have identified a biochemical and cellular mechanism whereby G6 inhibits Jak2-V617F mediated cellular proliferation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5127. doi:10.1158/1538-7445.AM2011-5127

Vascular smooth muscle Jak2 mediates angiotensin II-induced hypertension via increased levels of reactive oxygen species

AIMS

Angiotensin II (Ang II) type AT(1) receptors expressed on vascular smooth muscle cells (VSMCs) couple to the Jak2 signalling pathway. However, the importance of this tissue-specific coupling is poorly understood. The purpose of this investigation was to determine the importance of VSMC-derived Jak2 in angiotensin II-mediated hypertension.

METHODS AND RESULTS

The Cre-loxP system was used to conditionally eliminate Jak2 tyrosine kinase expression within the smooth muscle cells of mice. Following chronic Ang II infusion, the resulting increase in mean arterial pressure (MAP) was significantly attenuated in the Jak2 null mice when compared with littermate controls. The VSMC Jak2 null mice were also protected from the Ang II-induced vascular remodelling. Aortic rings from the VSMC Jak2 null mice exhibited reduced Ang II-induced contraction and enhanced endothelial-dependent relaxation via increased nitric oxide (NO) bioavailability. When compared with controls, the VSMC Jak2 nulls also had lower levels of hydrogen peroxide, Rho kinase activity, and intracellular Ca(2+) in response to Ang II.

CONCLUSIONS

The data indicate that VSMC Jak2 expression is involved in the pathogenesis of Ang II-dependent hypertension due to the increased presence of reactive oxygen species (ROS). As such, VSMC-derived Jak2 tyrosine kinase modulates overall vascular tone via multiple, non-redundant mechanisms.

Dimethylarginine dimethylaminohydrolase overexpression ameliorates atherosclerosis in apolipoprotein E-deficient mice by lowering asymmetric dimethylarginine

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is increasingly recognized as a novel biomarker in cardiovascular disease. To date, it remains unclear whether elevated ADMA levels are merely associated with cardiovascular risk or whether this molecule is of functional relevance in the pathogenesis of atherosclerotic vascular disease. To clarify this issue, we crossed dimethylarginine dimethylaminohydrolase (DDAH) transgenic mice that overexpress the human isoform 1 of the ADMA degrading enzyme DDAH into ApoE-deficient mice to generate ApoE(-/-)/hDDAH1(+/-) mice. In these mice, as well as ApoE(-/-) wild-type littermates, atherosclerosis within the aorta as well as vascular function of aortic ring preparations was assessed. We report here that overexpression of hDDAH1 reduces plaque formation in ApoE(-/-) mice by lowering ADMA. The extent of atherosclerosis closely correlated with plasma ADMA levels in male but not female mice fed either a standard rodent chow or an atherogenic diet. Functional analysis of aortic ring preparations revealed improved endothelial function in mice overexpressing hDDAH1. Our findings provide proof-of-principle that ADMA plays a causal role as a culprit molecule in atherosclerosis and support recent evidence indicating a functional relevance of DDAH enzymes in genetic mouse models. Together, these results demonstrate that pharmacological interventions targeting the ADMA/DDAH pathway may represent a novel approach in the prevention and management of cardiovascular diseases.

Role of dimethylarginine dimethylaminohydrolases in the regulation of endothelial nitric oxide production

Reduced NO is a hallmark of endothelial dysfunction, and among the mechanisms for impaired NO synthesis is the accumulation of the endogenous nitric-oxide synthase inhibitor asymmetric dimethylarginine (ADMA). Free ADMA is actively metabolized by the intracellular enzyme dimethylarginine dimethylaminohydrolase (DDAH), which catalyzes the conversion of ADMA to citrulline. Decreased DDAH expression/activity is evident in disease states associated with endothelial dysfunction and is believed to be the mechanism responsible for increased methylarginines and subsequent ADMA-mediated endothelial nitric-oxide synthase impairment. Two isoforms of DDAH have been identified; however, it is presently unclear which is responsible for endothelial ADMA metabolism and NO regulation. The current study investigated the effects of both DDAH-1 and DDAH-2 in the regulation of methylarginines and endothelial NO generation. Results demonstrated that overexpression of DDAH-1 and DDAH-2 increased endothelial NO by 24 and 18%, respectively. Moreover, small interfering RNA-mediated down-regulation of DDAH-1 and DDAH-2 reduced NO bioavailability by 27 and 57%, respectively. The reduction in NO production following DDAH-1 gene silencing was associated with a 48% reduction in l-Arg/ADMA and was partially restored with l-Arg supplementation. In contrast, l-Arg/ADMA was unchanged in the DDAH-2-silenced cells, and l-Arg supplementation had no effect on NO. These results clearly demonstrate that DDAH-1 and DDAH-2 manifest their effects through different mechanisms, the former of which is largely ADMA-dependent and the latter ADMA-independent. Overall, the present study demonstrates an important regulatory role for DDAH in the maintenance of endothelial function and identifies this pathway as a potential target for treating diseases associated with decreased NO bioavailability.

Ribonucleotide reductase inhibitors reduce atherosclerosis in a double-injury rabbit model

Atheroproliferative disorders such as atherosclerosis are an important health problem and one of the leading causes of morbidity and mortality in the United States. Minimally invasive therapeutic procedures, including angioplasty with stent deployment, are used frequently for obstructive coronary artery disease. However, restenosis, a proliferative vascular response, is a common sequela to this procedure. The current study investigated the effect of inhibiting ribonucleotide reductase (RR), an enzyme necessary for cellular proliferation, in an attempt to ameliorate the proliferative response. Two RR inhibitors, didox and hydroxyurea, were chosen for their potent antiproliferative properties. Studies were carried out by using a double-injury rabbit model, in which endothelial denudation was followed by the administration of a high-fat diet. At 4 wk after initial endothelial denudation, the developing atherosclerotic lesion was subjected to transluminal balloon dilation to simulate clinical intervention with percutaneous transluminal angioplasty. The degree of restenosis and atheroproliferation was assessed at 8 wk. Histologic evaluation of the lesion demonstrated that treatment with didox and hydroxyurea significantly decreased lesion area and lumen loss. These results suggest that RR inhibition may be an effective new tool for the treatment of atheroproliferative disorders.

Insulin-like growth factor binding protein-3 mediates vascular repair by enhancing nitric oxide generation

RATIONALE

Insulin-like growth factor binding protein (IGFBP)-3 modulates vascular development by regulating endothelial progenitor cell (EPC) behavior, specifically stimulating EPC cell migration. This study was undertaken to investigate the mechanism of IGFBP-3 effects on EPC function and how IGFBP-3 mediates cytoprotection following vascular injury.

OBJECTIVE

To examine the mechanism of IGFBP-3-mediated repair following vascular injury.

METHODS AND RESULTS

We used 2 complementary vascular injury models: laser occlusion of retinal vessels in adult green fluorescent protein (GFP) chimeric mice and oxygen-induced retinopathy in mouse pups. Intravitreal injection of IGFBP-3-expressing plasmid into lasered GFP chimeric mice stimulated homing of EPCs, whereas reversing ischemia induced increases in macrophage infiltration. IGFBP-3 also reduced the retinal ceramide/sphingomyelin ratio that was increased following laser injury. In the OIR model, IGFBP-3 prevented cell death of resident vascular endothelial cells and EPCs, while simultaneously increasing astrocytic ensheathment of vessels. For EPCs to orchestrate repair, these cells must migrate into ischemic tissue. This migratory ability is mediated, in part, by endogenous NO generation. Thus, we asked whether the migratory effects of IGFBP-3 were attributable to stimulation of NO generation. IGFBP-3 increased endothelial NO synthase expression in human EPCs leading to NO generation. IGFBP-3 exposure also led to the redistribution of vasodilator-stimulated phosphoprotein, an NO regulated protein critical for cell migration. IGFBP-3-mediated NO generation required high-density lipoprotein receptor activation and stimulation of phosphatidylinositol 3-kinase/Akt pathway.

CONCLUSION

These studies support consideration of IGFBP-3 as a novel agent to restore the function of injured vasculature and restore NO generation.

Role of the PRMT-DDAH-ADMA axis in the regulation of endothelial nitric oxide production

There is abundant evidence that the endothelium plays a crucial role in the maintenance of vascular tone and structure. One of the major endothelium-derived vasoactive mediators is nitric oxide (NO), formed in healthy vascular endothelium from the amino acid precursor l-arginine. Endothelial dysfunction is increased by various cardiovascular risk factors, metabolic diseases, and systemic or local inflammation. One mechanism that has been implicated in the development of endothelial dysfunction is the presence of elevated levels of asymmetric dimethylarginine (ADMA). Free ADMA, which is formed during proteolysis, is actively degraded by the intracellular enzyme dimethylarginine dimethylaminohydrolase (DDAH) which catalyzes the conversion of ADMA to citrulline and dimethylamine. It has been estimated that more than 70% of ADMA is metabolized by DDAH (Achan et al. [1]). Decreased DDAH expression/activity is evident in disease states associated with endothelial dysfunction and is believed to be the mechanism responsible for increased methylarginines and subsequent ADMA mediated eNOS impairment. However, recent studies suggest that DDAH may regulate eNOS activity and endothelial function through both ADMA-dependent and -independent mechanisms. In this regard, elevated plasma ADMA may serve as a marker of impaired methylarginine metabolism and the pathology previously attributed to elevated ADMA may be manifested, at least in part, through altered activity of the enzymes involved in ADMA regulation, specifically DDAH and PRMT.

Redox modification of ryanodine receptors underlies calcium alternans in a canine model of sudden cardiac death

AIMS

Although cardiac alternans is a known predictor of lethal arrhythmias, its underlying causes remain largely undefined in disease settings. The potential role of, and mechanisms responsible for, beat-to-beat alternations in the amplitude of systolic Ca(2+) transients (Ca(2+) alternans) was investigated in a canine post-myocardial infarction (MI) model of sudden cardiac death (SCD).

METHODS AND RESULTS

Post-MI dogs had preserved left ventricular (LV) function and susceptibility to ventricular fibrillation (VF) during exercise. LV wedge preparations from VF dogs were more susceptible to action potential (AP) alternans and the frequency-dependence of Ca(2+) alternans was shifted towards slower rates in myocytes isolated from VF dogs relative to controls. In both groups of cells, cytosolic Ca(2+) transients ([Ca(2+)](c)) alternated in phase with changes in diastolic Ca(2+) in sarcoplasmic reticulum ([Ca(2+)](SR)), but the dependence of [Ca(2+)](c) amplitude on [Ca(2+)](SR) was steeper in VF cells. Abnormal ryanodine receptor (RyR) function in VF cells was indicated by increased fractional Ca(2+) release for a given amplitude of Ca(2+) current and elevated diastolic RyR-mediated SR Ca(2+) leak. SR Ca(2+) uptake activity did not differ between VF and control cells. VF myocytes had an increased rate of reactive oxygen species production and increased RyR oxidation. Treatment of VF myocytes with reducing agents normalized parameters of Ca(2+) handling and shifted the threshold of Ca(2+) alternans to higher frequencies.

CONCLUSION

Redox modulation of RyRs promotes generation of Ca(2+) alternans by enhancing the steepness of the Ca(2+) release-load relationship and thereby providing a substrate for post-MI arrhythmias.

Chronic heart failure and the substrate for atrial fibrillation

AIMS

We sought to define the underlying mechanisms for atrial fibrillation (AF) during chronic heart failure (HF).

METHODS AND RESULTS

Preliminary studies showed that 4 months of HF resulted in irreversible systolic dysfunction (n = 9) and a substrate for sustained inducible AF (>3 months, n = 3). We used a chronic (4-month) canine model of tachypacing-induced HF (n = 10) to assess atrial electrophysiological remodelling, relative to controls (n = 5). Left ventricular fractional shortening was reduced from 37.2 +/- 0.83 to 13.44 +/- 2.63% (P < 0.05). Left atrial (LA) contractility (fractional area change) was reduced from 34.9 +/- 7.9 to 27.9 +/- 4.23% (P < 0.05). Action potential durations (APDs) at 50 and 90% repolarization were shortened by approximately 60 and 40%, respectively, during HF (P < 0.05). HF-induced atrial remodelling included increased fibrosis, increased I(to), and decreased I(K1), I(Kur), and I(Ks) (P < 0.05). HF induced increases in LA Kv channel interacting protein 2 (P < 0.05), no change in Kv4.3, Kv1.5, or Kir2.3, and reduced Kir2.1 (P < 0.05). When I(Ca-L) was elicited by action potential (AP) clamp, HF APs reduced the integral of I(Ca) in control myocytes, with a larger reduction in HF myocytes (P < 0.05). I(CaL) measured with standard voltage clamp was unchanged by HF. Incubation of myocytes with N-acetylcysteine (a glutathione precursor) attenuated HF-induced electrophysiological alterations. LA angiotensin-1 receptor expression was increased in HF.

CONCLUSION

Chronic HF causes alterations in ion channel expression and ion currents, resulting in attenuation of the APD and atrial contractility and a substrate for persistent AF.

Redox modification of ryanodine receptors contributes to sarcoplasmic reticulum Ca2+ leak in chronic heart failure

Abnormal cardiac ryanodine receptor (RyR2) function is recognized as an important factor in the pathogenesis of heart failure (HF). However, the specific molecular causes underlying RyR2 defects in HF remain poorly understood. In the present study, we used a canine model of chronic HF to test the hypothesis that the HF-related alterations in RyR2 function are caused by posttranslational modification by reactive oxygen species generated in the failing heart. Experimental approaches included imaging of cytosolic ([Ca(2+)](c)) and sarcoplasmic reticulum (SR) luminal Ca(2+) ([Ca(2+)]SR) in isolated intact and permeabilized ventricular myocytes and single RyR2 channel recording using the planar lipid bilayer technique. The ratio of reduced to oxidized glutathione, as well as the level of free thiols on RyR2 decreased markedly in failing versus control hearts consistent with increased oxidative stress in HF. RyR2-mediated SR Ca(2+) leak was significantly enhanced in permeabilized myocytes, resulting in reduced [Ca(2+)](SR) in HF compared to control cells. Both SR Ca(2+) leak and [Ca(2+)](SR) were partially normalized by treating HF myocytes with reducing agents. Conversely, oxidizing agents accelerated SR Ca(2+) leak and decreased [Ca(2+)](SR) in cells from normal hearts. Moreover, exposure to antioxidants significantly improved intracellular Ca(2+)-handling parameters in intact HF myocytes. Single RyR2 channel activity was significantly higher in HF versus control because of increased sensitivity to activation by luminal Ca(2+) and was partially normalized by reducing agents through restoring luminal Ca(2+) sensitivity oxidation of control RyR2s enhanced their luminal Ca(2+) sensitivity, thus reproducing the HF phenotype. These findings suggest that redox modification contributes to abnormal function of RyR2s in HF, presenting a potential therapeutic target for treating HF.

Air pollution exposure potentiates hypertension through reactive oxygen species-mediated activation of Rho/ROCK

OBJECTIVE

Fine particulate matter <2.5 microm (PM(2.5)) has been implicated in vasoconstriction and potentiation of hypertension in humans. We investigated the effects of short-term exposure to PM(2.5) in the angiotensin II (AII) infusion model.

METHODS AND RESULTS

Sprague-Dawley rats were exposed to PM(2.5) or filtered air (FA) for 10 weeks. At week 9, minipumps containing AII were implanted and the responses studied over a week. Mean concentration of PM(2.5) inside the chamber was 79.1+/-7.4 microg/m(3). After AII infusion, mean arterial pressure was significantly higher in PM(2.5)-AII versus FA-AII group. Aortic vasoconstriction to phenylephrine was potentiated with exaggerated relaxation to the Rho-kinase (ROCK) inhibitor Y-27632 and increase in ROCK-1 mRNA levels in the PM(2.5)-AII group. Superoxide (O(2).(-)) production in aorta was increased in the PM(2.5)-AII compared to the FA group, inhibitable by apocynin and L-NAME with coordinate upregulation of NAD(P)H oxidase subunits p22(phox) and p47(phox) and depletion of tetrahydrobiopterin. In vitro exposure to ultrafine particles (UFP) and PM(2.5) was associated with an increase in ROCK activity, phosphorylation of myosin light chain, and myosin phosphatase target subunit (MYPT1). Pretreatment with the nonspecific antioxidant N-acetylcysteine and the Rho kinase inhibitors (Fasudil and Y-27632) prevented MLC and MYPT-1 phosphorylation by UFP suggesting a O(2)(.-)-mediated mechanism for PM(2.5) and UFP effects.

CONCLUSIONS

Short-term air pollution exaggerates hypertension through O(2)(.-)-mediated upregulation of the Rho/ROCK pathway.

Regulation of eNOS-derived superoxide by endogenous methylarginines

The endogenous methylarginines, asymmetric dimethylarginine (ADMA) and N (G)-monomethyl- l-arginine (L-NMMA) regulate nitric oxide (NO) production from endothelial NO synthase (eNOS). Under conditions of tetrahydrobiopterin (BH 4) depletion eNOS also generates (*)O 2 (-); however, the effects of methylarginines on eNOS-derived (*)O 2 (-) generation are poorly understood. Therefore, using electron paramagnetic resonance spin trapping techniques we measured the dose-dependent effects of ADMA and L-NMMA on (*)O 2 (-) production from eNOS under conditions of BH 4 depletion. In the absence of BH 4, ADMA dose-dependently increased NOS-derived (*)O 2 (-) generation, with a maximal increase of 151% at 100 microM ADMA. L-NMMA also dose-dependently increased NOS-derived (*)O 2 (-), but to a lesser extent, demonstrating a 102% increase at 100 microM L-NMMA. Moreover, the native substrate l-arginine also increased eNOS-derived (*)O 2 (-), exhibiting a similar degree of enhancement as that observed with ADMA. Measurements of NADPH consumption from eNOS demonstrated that binding of either l-arginine or methylarginines increased the rate of NADPH oxidation. Spectrophotometric studies suggest, just as for l-arginine and L-NMMA, the binding of ADMA shifts the eNOS heme to the high-spin state, indicative of a more positive heme redox potential, enabling enhanced electron transfer from the reductase to the oxygenase site. These results demonstrate that the methylarginines can profoundly shift the balance of NO and (*)O 2 (-) generation from eNOS. These observations have important implications with regard to the therapeutic use of l-arginine and the methylarginine-NOS inhibitors in the treatment of disease.

Mechanism of 4-HNE mediated inhibition of hDDAH-1: implications in no regulation

Nitric oxide synthase is inhibited by NG-methylated derivatives of arginine whose cellular levels are controlled by dimethylarginine dimethylamino-hydrolase (DDAH). DDAH-1 is a Zn(II)-containing enzyme that through hydrolysis of methylated l-arginines regulates the activity of NOS. Herein, we report the kinetic properties of hDDAH-1 and its redox-dependent regulation. Kinetic studies using recombinant enzyme demonstrated Km values of 68.7 and 53.6 microM and Vmax values of 356 and 154 nmols/mg/min for ADMA and L-NMMA, respectively. This enzymatic activity was selective for free ADMA and L-NMMA and was incapable of hydrolyzing peptide incorporated methylarginines. Subsequent studies performed to determine the effects of reactive oxygen and reactive nitrogen species on DDAH activity demonstrated that low level oxidant exposure had little effect on enzyme activity and that concentrations approaching >or=100 microM were needed to confer significant inhibition of DDAH activity. However, exposure of DDAH to the lipid oxidation product, 4-HNE, dose-dependently inhibited DDAH activity with 15% inhibition observed at 10 microM, 50% inhibition at 50 microM, and complete inhibition at 500 microM. Mass spectrometry analysis demonstrated that the mechanism of inhibition resulted from the formation of Michael adducts on His 173, which lies within the active site catalytic triad of hDDAH-1. These studies were performed with pathophysiologicaly relevant concentrations of this lipid peroxidation product and suggest that DDAH activity can be impaired under conditions of increased oxidative stress. Because DDAH is the primary enzyme involved in methylarginine metabolism, the loss of activity of this enzyme would result in impaired NOS activity and reduced NO bioavailability.

Role of DDAH-1 in lipid peroxidation product-mediated inhibition of endothelial NO generation

Altered nitric oxide (NO) biosynthesis is thought to play a role in the initiation and progression of atherosclerosis and may contribute to increased risk seen in other cardiovascular diseases. It is hypothesized that altered NO bioavailability may result from an increase in endogenous NO synthase (NOS) inhibitors, asymmetric dimethly araginine (ADMA), and N(G)-monomethyl arginine, which are normally metabolized by dimethyarginine dimethylamine hydrolase (DDAH). Lipid hydroperoxides and their degradation products are generated during inflammation and oxidative stress and have been implicated in the pathogenesis of cardiovascular disorders. Here, we show that the lipid hydroperoxide degradation product 4-hydroxy-2-nonenal (4-HNE) causes a dose-dependent decrease in NO generation from bovine aortic endothelial cells, accompanied by a decrease in DDAH enzyme activity. The inhibitory effects of 4-HNE (50 microM) on endothelial NO production were partially reversed with L-Arg supplementation (1 mM). Overexpression of human DDAH-1 along with antioxidant supplementation completely restored endothelial NO production following exposure to 4-HNE (50 microM). These results demonstrate a critical role for the endogenous methylarginines in the pathogenesis of endothelial dysfunction. Because lipid hydroperoxides and their degradation products are known to be involved in atherosclerosis, modulation of DDAH and methylarginines may serve as a novel therapeutic target in the treatment of cardiovascular disorders associated with oxidative stress.

Myocardial ischemia results in tetrahydrobiopterin (BH4) oxidation with impaired endothelial function ameliorated by BH4

Coronary vasodilation is impaired in the postischemic heart with a loss of endothelial nitric oxide synthase (eNOS) activity, but the mechanisms underlying ischemia-induced eNOS dysfunction are not understood. For nitric oxide (NO) synthesis, eNOS requires the redox-sensitive cofactor tetrahydrobiopterin (BH(4)); however, the role of BH(4) in ischemia-induced endothelial dysfunction remains unknown. Therefore, isolated rat hearts were subjected to varying durations of ischemia, and the alterations in NOS-dependent vasodilation were measured and correlated with assays of eNOS activity and cardiac BH(4) concentrations. Ischemia time-dependently decreased cardiac BH(4) content with 85, 95, or 97% irreversible degradation after 30, 45, or 60 min of ischemia, respectively. Paralleling the decreases in BH(4), reductions of eNOS activity were seen of 58, 86, or 92%, and NOS-derived superoxide production was greatly increased. Addition of 10 microM BH(4) enhanced eNOS activity in nonischemic hearts and partially restored activity after ischemia. It also suppressed NOS-derived superoxide production. Impaired coronary flow during postischemic reperfusion was improved by BH(4) infusion. Thus, BH(4) depletion contributes to postischemic eNOS dysfunction, and BH(4) treatment is effective in partial restoration of endothelium-dependent coronary flow. Supplementation of BH(4) may therefore be an important therapeutic approach to reverse endothelial dysfunction in postischemic tissues.

Expression of SERCA isoform with faster Ca2+ transport properties improves postischemic cardiac function and Ca2+ handling and decreases myocardial infarction

Myocardial ischemia-reperfusion (I/R) injury is associated with contractile dysfunction, arrhythmias, and myocyte death. Intracellular Ca(2+) overload with reduced activity of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) is a critical mechanism of this injury. Although upregulation of SERCA function is well documented to improve postischemic cardiac function, there are conflicting reports where pharmacological inhibition of SERCA improved postischemic function. SERCA2a is the primary cardiac isoform regulating intracellular Ca(2+) homeostasis; however, SERCA1a has been shown to substitute SERCA2a with faster Ca(2+) transport kinetics. Therefore, to further address this issue and to evaluate whether SERCA1a expression could improve postischemic cardiac function and myocardial salvage, in vitro and in vivo myocardial I/R studies were performed on SERCA1a transgenic (SERCA1a(+/+)) and nontransgenic (NTG) mice. Langendorff-perfused hearts were subjected to 30 min of global ischemia followed by reperfusion. Baseline preischemic coronary flow and left ventricular developed pressure were significantly greater in SERCA1a(+/+) mice compared with NTG mice. Independent of reperfusion-induced oxidative stress, SERCA1a(+/+) hearts demonstrated greatly improved postischemic (45 min) contractile recovery with less persistent arrhythmias compared with NTG hearts. Morphometry showed better-preserved myocardial structure with less infarction, and electron microscopy demonstrated better-preserved myofibrillar and mitochondrial ultrastructure in SERCA1a(+/+) hearts. Importantly, intraischemic Ca(2+) levels were significantly lower in SERCA1a(+/+) hearts. The cardioprotective effect of SERCA1a was also observed during in vivo regional I/R with reduced myocardial infarct size after 24 h of reperfusion. Thus SERCA1a(+/+) hearts were markedly protected against I/R injury, suggesting that expression of SERCA 1a isoform reduces postischemic Ca(2+) overload and thus provides potent myocardial protection.

4-Aryl-1,3,2-oxathiazolylium-5-olates as pH-Controlled NO-Donors: The Next Generation ofS-Nitrosothiols

S-Nitrosothiols (RSNOs) are important exogenous and endogenous sources of nitric oxide (NO) in biological systems. A series of 4-aryl-1,3,2-oxathiazolylium-5-olates derivatives with varying aryl para-substituents (-CF3, -H, -Cl, and -OCH3) were synthesized. These compounds were found to release NO under acidic condition (pH = 5). The decomposition pathway of the aryloxathiazolyliumolates proceeded via an acid-catalyzed ring-opening mechanism after which NO was released and an S-centered radical was generated. Electron paramagnetic resonance (EPR) spin trapping studies were performed to detect NO and the S-centered radical using the spin traps of iron(II) N-methyl-D-glucamine dithiocarbamate [(MGD)2-FeII] and 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Also, EPR spin trapping and UV-vis spectrophotometry were used to analyze the effect of aryl para substitution on the NO-releasing property of aryloxathiazolyliumolates. The results showed that the presence of an electron-withdrawing substituent such as -CF3 enhanced the NO-releasing capability of the aryloxathiazolyliumolates, whereas an electron-donating substituent like methoxy (-OCH3) diminished it. Computational studies using density functional theory (DFT) at the PCM/B3LYP/6-31+G**//B3LYP/6-31G* level were used to rationalize the experimental observations. The aryloxathiazolyliumolates diminished susceptibility to reduction by ascorbate or gluthathione, and their capacity to cause vasodilation as compared to other S-nitrosothiols suggests potential application in biological systems.

Characterization of in vivo tissue redox status, oxygenation, and formation of reactive oxygen species in postischemic myocardium

The current study aims to characterize the alterations of in vivo tissue redox status, oxygenation, formation of reactive oxygen species (ROS), and their effects on the postischemic heart. Mouse heart was subjected to 30 min LAD occlusion, followed by 60 min reperfusion. In vivo myocardial redox status and oxygenation were measured with electron paramagnetic resonance (EPR). In vivo tissue NAD(P)H and formation of ROS were monitored with fluorometry. Tissue glutathione/glutathione disulfide (GSH/GSSG) levels were detected with high-performance liquid chromatography (HPLC). These experiments demonstrated that tissue reduction rate of nitroxide was increased 100% during ischemia and decreased 33% after reperfusion compared to the nonischemic tissue. There was an overshoot of tissue oxygenation after reperfusion. Tissue NAD(P)H levels were increased during and after ischemia. There was a burst formation of ROS at the beginning of reperfusion. Tissue GSH/GSSG level showed a 48% increase during ischemia and 29% decrease after reperfusion. In conclusion, the hypoxia during ischemia limited mitochondrial respiration and caused a shift of tissue redox status to a more reduced state. ROS generated at the beginning of reperfusion caused a shift of redox status to a more oxidized state, which may contribute to the postischemic myocardial injury.

Cyclic AMP signaling contributes to neural plasticity and hyperexcitability in AH sensory neurons following intestinal Trichinella spiralis-induced inflammation

Trichinella spiralis infection causes hyperexcitability in enteric after-hyperpolarising (AH) sensory neurons that is mimicked by neural, immune or inflammatory mediators known to stimulate adenylyl cyclase (AC)/cyclic 3',5'-adenosine monophosphate (cAMP) signaling. The hypothesis was tested that ongoing modulation and sustained amplification in the AC/cAMP/phosphorylated cAMP related element binding protrein (pCREB) signaling pathway contributes to hyperexcitability and neuronal plasticity in gut sensory neurons after nematode infection. Electrophysiological, immunological, molecular biological or immunochemical studies were done in T. spiralis-infected guinea-pigs (8000 larvae or saline) after acute-inflammation (7 days) or 35 days p.i., after intestinal clearance. Acute-inflammation caused AH-cell hyperexcitability and elevated mucosal and neural tissue levels of myeloperoxidase, mast cell tryptase, prostaglandin E2, leukotrine B4, lipid peroxidation, nitric oxide and gelatinase; lower level inflammation persisted 35 days p.i. Acute exposure to blockers of AC, histamine, cyclooxygenase or leukotriene pathways suppressed AH-cell hyperexcitability in a reversible manner. Basal cAMP responses or those evoked by forskolin (FSK), Ro-20-1724, histamine or substance P in isolated myenteric ganglia were augmented after T. spiralis infection; up-regulation also occurred in AC expression and AC-immunoreactivity in calbindin (AH) neurons. The cAMP-dependent slow excitatory synaptic transmission-like responses to histamine (mast cell mediator) or substance P (neurotransmitter) acting via G-protein coupled receptors (GPCR) in AH neurons were augmented by up to 2.5-fold after T. spiralis infection. FSK, histamine, substance P or T. spiralis acute infection caused a 5- to 30-fold increase in cAMP-dependent nuclear CREB phosphorylation in isolated ganglia or calbindin (AH) neurons. AC and CREB phosphorylation remained elevated 35 days p.i.. Ongoing immune activation, AC up-regulation, enhanced phosphodiesterase IV activity and facilitation of the GPCR-AC/cAMP/pCREB signaling pathway contributes to T. spiralis-induced neuronal plasticity and AH-cell hyperexcitability. This may be relevant in gut nematode infections and inflammatory bowel diseases, and is a potential therapeutic target.

Evidence for the pathophysiological role of endogenous methylarginines in regulation of endothelial NO production and vascular function

In endothelium, NO is derived from endothelial NO synthase (eNOS)-mediated L-arginine oxidation. Endogenous guanidinomethylated arginines (MAs), including asymmetric dimethylarginine (ADMA) and NG-methyl-L-arginine (L-NMMA), are released in cells upon protein degradation and are competitive inhibitors of eNOS. However, it is unknown whether intracellular MA concentrations reach levels sufficient to regulate endothelial NO production. Therefore, the dose-dependent effects of ADMA and L-NMMA on eNOS function were determined. Kinetic studies demonstrated that the Km for L-arginine is 3.14 microM with a Vmax of 0.14 micromol mg-1 min-1, whereas Ki values of 0.9 microM and 1.1 microM were determined for ADMA and L-NMMA, respectively. EPR studies of NO production from purified eNOS demonstrated that, with a physiological 100 microM level of L-arginine, MA levels of >10 microM were required for significant eNOS inhibition. Dose-dependent inhibition of NO formation in endothelial cells was observed with extracellular MA concentrations as low 5 microm. Similar effects were observed in isolated vessels where 5 microm ADMA inhibited vascular relaxation to acetylcholine. MA uptake studies demonstrated that ADMA and L-NMMA accumulate in endothelial cells with intracellular levels greatly exceeding extracellular concentrations. L-arginine/MA ratios were correlated with cellular NO production. Although normal physiological levels of MAs do not significantly inhibit NOS, a 3- to 9-fold increase, as reported under disease conditions, would exert prominent inhibition. Using a balloon model of vascular injury, approximately 4-fold increases in cellular MAs were observed, and these caused prominent impairment of vascular relaxation. Thus, MAs are critical mediators of vascular dysfunction following vascular injury.

ADOA3R as a therapeutic target in experimental colitis: proof by validated high-density oligonucleotide microarray analysis

Adenosine A3 receptors (ADOA3Rs) are emerging as novel purinergic targets for treatment of inflammatory diseases. Our goal was to assess the protective effect of the ADOA3R agonist N(6)-(3-iodobenzyl)-adenosine-5-N-methyluronamide (IB-MECA) on gene dysregulation and injury in a rat chronic model of 2,4,6-trinitrobenzene sulfonic acid (TNBS)--induced colitis. It was necessary to develop and validate a microarray technique for testing the protective effects of purine-based drugs in experimental inflammatory bowel disease. High-density oligonucleotide microarray analysis of gene dysregulation was assessed in colons from normal, TNBS-treated (7 days), and oral IB-MECA-treated rats (1.5 mg/kg b.i.d.) using a rat RNU34 neural GeneChip of 724 genes and SYBR green polymerase chain reaction. Analysis included clinical evaluation, weight loss assessment, and electron paramagnetic resonance imaging/spin-trap monitoring of free radicals. Remarkable colitis-induced gene dysregulation occurs in the most exceptional cluster of 5.4% of the gene pool, revealing 2 modes of colitis-related dysregulation. Downregulation occurs in membrane transporter, mitogen-activated protein (MAP) kinase, and channel genes. Upregulation occurs in chemokine, cytokine/inflammatory, stress, growth factor, intracellular signaling, receptor, heat shock protein, retinoid metabolism, neural, remodeling, and redox-sensitive genes. Oral IB-MECA prevented dysregulation in 92% of these genes, histopathology, gut injury, and weight loss. IB-MECA or adenosine suppressed elevated free radicals in ex vivo inflamed gut. Oral IB-MECA blocked the colitis-induced upregulation (<or=20-fold) of Bzrp, P2X1R, P2X4R, P2X7R, P2Y2R, P2Y6R, and A2aR/A2bR but not A1R or A3R genes or downregulated P2X2R, P2Y1R, and P2Y4R. Real-time SYBR green polymerase chain reaction validated gene chip data for both induction of colitis and treatment with IB-MECA for >90% of genes tested (33 of 37 genes). We conclude that our validated high-density oligonucleotide microarray analysis is a powerful technique for molecular gene dysregulation studies to assess the beneficial effects of purine-based or other drugs in experimental colitis. ADOA3R is new potential therapeutic target for inflammatory bowel disease.

Apigenin-induced-apoptosis is mediated by the activation of PKCdelta and caspases in leukemia cells

Apigenin, a flavone abundantly found in fruits and vegetables, exhibits antiproliferative, anti-inflammatory, and antimetastatic activities through poorly defined mechanisms. In the present study, the treatment of different cell lines with apigenin resulted in selective antiproliferative and apoptotic effect in monocytic and lymphocytic leukemias. Apigenin-induced-apoptosis was mediated by the activation of caspase-9 and caspase-3. Apigenin was found intracellularly and localized to the mitochondria. Treatment of monocytic cells with apigenin was accompanied by an increase in reactive oxygen species (ROS) and phosphorylation of the MAPKs, p38 and ERK. However, the inhibition of ROS, p38 or ERK failed to block apoptosis, suggesting that these cellular responses induced by apigenin are not essential for the induction of apoptosis. In addition, apigenin induced the activation of PKCdelta. Pharmacological inhibition of PKCdelta, the expression of dominant-negative PKCdelta and silencing of PKCdelta in leukemia cells showed that apigenin-induced-apoptosis requires PKCdelta activity. Together, these results indicate that this flavonoid provides selective activity to promote caspase-dependent-apoptosis of leukemia cells and uncover an essential role of PKCdelta during the induction of apoptosis by apigenin.

Hydroxylation of d-phenylalanine as a novel approach to detect hydroxyl radicals: Application to cardiac pathophysiology

OBJECTIVE

Research in the pathophysiology of ischemia/reperfusion or redox signaling is hindered by lack of simple methodology to measure short-lived oxygen radicals. In the presence of hydroxyl radical ((*)OH), d-phenylalanine (d-Phe) yields para-, meta- and ortho-tyrosine. We have previously demonstrated that d-Phe can accurately detect (*)OH formation in chemical, enzymatic and cellular systems by simple HPLC methodology [Anal Biochem 290:138;2001]. In the present study, we tested whether d-Phe hydroxylation can be used to detect (*)OH formation in intact organs.

METHODS

Rat hearts were perfused with buffer containing 5 mM d-Phe and subjected to 30 min of total global ischemia at 37 degrees C followed by 45 min of reperfusion. Quantitative analysis of the three hydroxytyrosine isomers was achieved by HPLC-based electrochemical detection of cardiac venous effluent, with the analytical cells operating in the oxidative mode. The detection limit of this assay was <10 fmol.

RESULTS

Under baseline conditions, hydroxytyrosine release from the heart was very low ( congruent with0.8 nmol/min/g). However, a prominent tyrosine burst occurred immediately upon post-ischemic reflow. In cardiac effluent collected 40 s into reperfusion, the hydroxytyrosine concentration was more than 40 times greater than at baseline; hydroxytyrosine concentration then progressively declined, to return to pre-ischemic values by 5 min of reperfusion. In parallel experiments, formation of hydroxytyrosines was markedly reduced in hearts reperfused in the presence of the (*)OH scavenger mannitol. Inclusion of 5 mm d-Phe in the perfusion medium altered neither basal cardiac function nor coronary vascular tone, but it enhanced recovery of myocardial function during post-ischemic reperfusion, consistent with direct reaction with (*)OH.

CONCLUSION

Our results demonstrate that d-Phe is a sensitive method for detection of (*)OH generation in the heart. Since d-Phe is not a substrate for endogenous enzymes, it can be exploited as a reliable method to measure (*)OH formation under a variety of pathophysiological conditions.

Heat shock protects cardiac cells from doxorubicin-induced toxicity by activating p38 MAPK and phosphorylation of small heat shock protein 27

Doxorubicin (DOX) and its derivatives are used as chemotherapeutic drugs to treat cancer patients. However, production of DOX-mediated reactive oxygen species (ROS) by prolonged use of these drugs has been found to cause dilative cardiomyopathy and congestive heart failure. Thus various preventive modalities have been developed to avoid this side effect. We have found that the DOX-mediated oxidant-induced toxicity in cardiac cells could be minimized by hyperthermia-induced small heat shock protein 27 (HSP27); that is, this protein acts as an endogenous antioxidant against DOX-derived oxidants such as H(2)O(2). Heat shock-induced HSP27 was found to act as an antiapoptotic protein (reducing ROS and Bax-to-Bcl2 ratio) against DOX, and its phosphorylated isoforms stabilized F-actin remodeling in DOX-treated cardiac cells and, hence, attenuated the toxicity. Protein kinase assays and proteomic analyses suggested that higher expression of HSP27 and its phosphorylation are responsible for the protection in heat-shocked cells. Two-dimensional gel electrophoresis showed six isoforms (nonphosphorylated and phosphorylated) of HSP27. Matrix-assisted laser desorption/ionization time of flight analyses showed alpha- and beta-isoforms of HSP27, which are phosphorylated by various protein kinases. Ser(15) and Ser(85) phosphorylation of HSP27 by MAPK-assisted protein kinase 2 was found to be the key mechanism in reduction of apoptosis and facilitation of F-actin remodeling. The present study illustrates that hyperthermia protects cells from DOX-induced death through induction and phosphorylation of HSP27 and its antiapoptotic and actin-remodeling activities.

Characterization of the Mechanism of Cytochrome P450 Reductase-Cytochrome P450-mediated Nitric Oxide and Nitrosothiol Generation from Organic Nitrates

Mammalian cytochrome P450 reductase (CPR) and cytochrome P450 (CP) play important roles in organic nitrate bioactivation; however, the mechanism by which they convert organic nitrate to NO remains unknown. Questions remain regarding the initial precursor of NO that serves to link organic nitrate to the activation of soluble guanylyl cyclase (sGC). To characterize the mechanism of CPR-CP-mediated organic nitrate bioactivation, EPR, chemiluminescence NO analyzer, NO electrode, and immunoassay studies were performed. With rat hepatic microsomes or purified CPR, the presence of NADPH triggered organic nitrate reduction to NO2(-). The CPR flavin site inhibitor diphenyleneiodonium inhibited this NO2(-) generation, whereas the CP inhibitor clotrimazole did not. However, clotrimazole greatly inhibited NO2(-)-dependent NO generation. Therefore, CPR catalyzes organic nitrate reduction, producing nitrite, whereas CP can mediate further nitrite reduction to NO. Nitrite-dependent NO generation contributed <10% of the CPR-CP-mediated NO generation from organic nitrates; thus, NO2(-) is not the main precursor of NO. CPR-CP-mediated NO generation was largely thiol-dependent. Studies suggested that organic nitrite (R-O-NO) was produced from organic nitrate reduction by CPR. Further reaction of organic nitrite with free or microsome-associated thiols led to NO or nitrosothiol generation and thus stimulated the activation of sGC. Thus, organic nitrite is the initial product in the process of CRP-CP-mediated organic nitrate activation and is the precursor of NO and nitrosothiols, serving as the link between organic nitrate and sGC activation.