Effects of in vivo nitroglycerin treatment on activity and expression of the guanylyl cyclase and cGMP-dependent protein kinase and their downstream target vasodilator-stimulated phosphoprotein in aorta

Tobacco smoking and vascular biology and function: evidence from human studies

Tobacco cigarette smoking is among the most complex and least understood health risk factors. A deeper insight into the pathophysiological actions of smoking exposure is of special importance as smoking is a major cause of chronic non-communicable diseases, in particular of cardiovascular disease as well as risk factors such as atherosclerosis and arterial hypertension. It is well known that smoking exerts its negative effects on cardiovascular health through various interdependent pathophysiological actions including hemodynamic and autonomic alterations, oxidative stress, inflammation, endothelial dysfunction, thrombosis, and hyperlipidemia. Importantly, impaired vascular endothelial function is acknowledged as an early key event in the initiation and progression of smoking-induced atherosclerosis. Increasing evidence from human studies indicates that cigarette smoke exposure associates with a pathological state of the vascular endothelium mainly characterized by reduced vascular nitric oxide bioavailability due to increased vascular superoxide production. In the present overview, we provide compact evidence on the effects of tobacco cigarette smoke exposure on vascular biology and function in humans centered on main drivers of adverse cardiovascular effects including endothelial dysfunction, inflammation, and oxidative stress.

Protective Effects of Short-Chain Fatty Acids on Endothelial Dysfunction Induced by Angiotensin II

Short-chain fatty acids (SCFAs) are among the main classes of bacterial metabolic products and are mainly synthesized in the colon through bacterial fermentation. Short-chain fatty acids, such as acetate, butyrate, and propionate, reduce endothelial activation induced by proinflammatory mediators, at least in part, by activation of G protein–coupled receptors (GPRs): GPR41 and GPR43. The objective of the study was to analyze the possible protective effects of SCFAs on endothelial dysfunction induced by angiotensin II (AngII). Rat aortic endothelial cells (RAECs) and rat aortas were incubated with AngII (1 μM) for 6 h in the presence or absence of SCFAs (5–10 mM). In RAECs, we found that AngII reduces the production of nitric oxide (NO) stimulated by calcium ionophore A23187; increases the production of reactive oxygen species (ROS), both from the nicotinamide adenine dinucleotide phosphate oxidase system and the mitochondria; diminishes vasodilator-stimulated phosphoprotein (VASP) phosphorylation at Ser²³⁹; reduces GPR41 and GPR43 mRNA level; and reduces the endothelium-dependent relaxant response to acetylcholine in aorta. Coincubation with butyrate and acetate, but not with propionate, increases both NO production and pSer²³⁹-VASP, reduces the concentration of intracellular ROS, and improves relaxation to acetylcholine. The beneficial effects of butyrate were inhibited by the GPR41 receptor antagonist, β-hydroxybutyrate, and by the GPR43 receptor antagonist, GLPG0794. Butyrate inhibited the down-regulation of GPR41 and GPR43 induced by AngII, being without effect acetate and propionate. Neither β-hydroxybutyrate nor GLPG0794 affects the protective effect of acetate in endothelial dysfunction. In conclusion, acetate and butyrate improve endothelial dysfunction induced by AngII by increasing the bioavailability of NO. The effect of butyrate seems to be related to GPR41/43 activation, whereas acetate effects were independent of GPR41/43.

NF-κB-responsive miR-155 induces functional impairment of vascular smooth muscle cells by downregulating soluble guanylyl cyclase

Vascular smooth muscle cells (VSMCs) play an important role in maintaining vascular function. Inflammation-mediated VSMC dysfunction leads to atherosclerotic intimal hyperplasia and preeclamptic hypertension; however, the underlying mechanisms are not clearly understood. We analyzed the expression levels of microRNA-155 (miR-155) in cultured VSMCs, mouse vessels, and clinical specimens and then assessed its role in VSMC function. Treatment with tumor necrosis factor-α (TNF-α) elevated miR-155 biogenesis in cultured VSMCs and vessel segments, which was prevented by NF-κB inhibition. MiR-155 expression was also increased in high-fat diet-fed ApoE^−/− mice and in patients with atherosclerosis and preeclampsia. The miR-155 levels were inversely correlated with soluble guanylyl cyclase β1 (sGCβ1) expression and nitric oxide (NO)-dependent cGMP production through targeting the sGCβ1 transcript. TNF-α-induced miR-155 caused VSMC phenotypic switching, which was confirmed by the downregulation of VSMC-specific marker genes, suppression of cell proliferation and migration, alterations in cell morphology, and NO-induced vasorelaxation. These events were mitigated by miR-155 inhibition. Moreover, TNF-α did not cause VSMC phenotypic modulation and limit NO-induced vasodilation in aortic vessels of miR-155^−/− mice. These findings suggest that NF-κB-induced miR-155 impairs the VSMC contractile phenotype and NO-mediated vasorelaxation by downregulating sGCβ1 expression. These data suggest that NF-κB-responsive miR-155 is a novel negative regulator of VSMC functions by impairing the sGC/cGMP pathway, which is essential for maintaining the VSMC contractile phenotype and vasorelaxation, offering a new therapeutic target for the treatment of atherosclerosis and preeclampsia.

The overexpression of a microRNA molecule adversely affects the functioning of vascular smooth muscle cells (VSMCs) and may contribute to the development of artherosclerosis and preeclampsia. The interactions between VSMCs and the cells lining blood vessels (endothelium) are crucial for maintaining the healthy phenotype and relaxation of blood vessels. Disruption to these interactions via inflammation, for example, can trigger serious vascular diseases. Young-Myeong Kim at Kangwon National University, Chungcheon, South Korea, and co-workers demonstrated that expression levels of a microRNA-155 are elevated in patients with artherosclerosis and preeclampsia, while an enzyme found in VSMCs called soluble guanylyl cyclase is considerably reduced. Using human and mice tissues, the team showed that miR-155 impairs the contractile phenotype and relaxation of VSMCs by reducing guanylyl cyclase expression. Their findings may inform new therapies for vascular diseases.

Decreased PKG transcription mediated by PI3K/Akt/FoxO1 pathway is involved in the development of nitroglycerin tolerance

Phosphoinositide 3-kinase (PI3K)/Akt plays a pivotal role in the vascular response. The present study is to determine whether PI3K/Akt pathway in vascular smooth muscle cells is involved in nitroglycerin (NTG) tolerance and the underlying mechanism. Nitrate tolerance of porcine coronary arteries in vitro was induced by incubation of NTG (10^-5 M) for 24 h. Nitrate tolerance in vivo was obtained by subcutaneous injection of mice with NTG (20 mg kg^-1, tid, 3 days) and the aortas were used. Protein levels of total and phosphorylated Akt, forkhead box protein O1 (FoxO1), and cGMP-dependent protein kinase (PKG) were determined by western blot analysis. Isometric vessel tension was recorded by organ chamber technique. PKG mRNA was determined by real-time PCR. The cellular translocation of FoxO1 was observed by immunofluorescence. Reactive oxygen species (ROS) level was measured by DHE staining. The vascular relaxation to NTG was significantly inhibited in in vivo and in vitro NTG tolerant arteries. Meanwhile, the protein level of phosphorylated Akt at Ser473 was increased in the tolerant arteries. The attenuated relaxation and the augmented Akt-p were ameliorated by LY294002, a specific inhibitor of PI3K. The protein and mRNA expression of PKG were significantly down-regulated in NTG tolerant arteries, which were reversed by LY294002. The level of phosphorylated FoxO1 at Ser256 and its translocation from the nucleus to the cytosol were both increased in NTG tolerance and were also inhibited by LY294002. ROS production was significantly increased in NTG tolerant arteries, which was not be affected by LY294002 but inhibited by N-acetyl-L-cysteine. In conclusion, the present study suggests that PI3K/Akt in vascular smooth muscle is involved in the development of NTG tolerance via inhibiting PKG transcription and the effect is mediated by FoxO1.

Achieving Canadian physical activity guidelines is associated with better vascular function independent of aerobic fitness and sedentary time in older adults

Canadian physical activity guidelines recommend older adults accumulate 150 min of weekly moderate to vigorous physical activity (MVPA). Older adults who are insufficiently active may have reduced blood vessel health and an increased risk of cardiovascular disease. We tested this hypothesis in 11 older adults who did (7 female; age, 65 ± 5 years; MVPA, = 239 ± 81 min/week) and 10 older adults who did not (7 female; age, 68 ± 9 years; MVPA, 95 ± 33 min/week) meet MVPA guidelines. Flow-mediated dilation (FMD) in the brachial (BA) and popliteal (POP) arteries, as well as nitroglycerin-mediated dilation (NMD; endothelial-independent dilation) in the POP were assessed via ultrasonography. Aerobic fitness (peak oxygen uptake) was determined using a graded, maximal cycle ergometry test via indirect calorimetry. MVPA and sedentary time were assessed over 5 days using the PiezoRx and activPAL, respectively. There were no differences in peak oxygen uptake (26 ± 10 vs. 22 ± 10 mL O₂/(kg·min); p = 0.26) or sedentary time (512 ± 64 vs. 517 ± 76 min/day; p = 0.87) between groups; however, those who achieved the MVPA guidelines had a higher BA-FMD (5.1% ± 1.3% vs. 3.6% ± 1.7%; p = 0.03), POP-FMD (2.6% ± 1.1% vs. 1.3% ± 0.8%; p = 0.006), and POP-NMD (5.1% ± 1.7% vs. 3.3% ± 2.1%; p = 0.04). In the pooled sample, MVPA was moderately correlated to both BA-FMD (r = 0.53; p = 0.01) and POP-NMD (r = 0.59; p = 0.005), and strongly correlated to POP-FMD (r = 0.85; p < 0.001). Collectively, our results provide supporting evidence that meeting MVPA guidelines is associated with better vascular function and may reduce the risk of developing cardiovascular disease in older adults. Furthermore, these data suggest that weekly MVPA time may have a greater impact on blood vessel function than aerobic fitness and weekly sedentary time.

Roles of Endoplasmic Reticulum Stress in NECA-Induced Cardioprotection against Ischemia/Reperfusion Injury

OBJECTIVE

This study aimed to investigate whether the nonselective A2 adenosine receptor agonist NECA induces cardioprotection against myocardial ischemia/reperfusion (I/R) injury via glycogen synthase kinase 3β (GSK-3β) and the mitochondrial permeability transition pore (mPTP) through inhibition of endoplasmic reticulum stress (ERS).

METHODS AND RESULTS

H9c2 cells were exposed to H2O2 for 20 minutes. NECA significantly prevented H2O2-induced TMRE fluorescence reduction, indicating that NECA inhibited the mPTP opening. NECA blocked H2O2-induced GSK-3β phosphorylation and GRP94 expression. NECA increased GSK-3β phosphorylation and decreased GRP94 expression, which were prevented by both ERS inductor 2-DG and PKG inhibitor KT5823, suggesting that NECA may induce cardioprotection through GSK-3β and cGMP/PKG via ERS. In isolated rat hearts, both NECA and the ERS inhibitor TUDCA decreased myocardial infarction, increased GSK-3β phosphorylation, and reversed GRP94 expression at reperfusion, suggesting that NECA protected the heart by inhibiting GSK-3β and ERS. Transmission electron microscopy showed that NECA and TUDCA reduced mitochondrial swelling and endoplasmic reticulum expansion, further supporting that NECA protected the heart by preventing the mPTP opening and ERS.

CONCLUSION

These data suggest that NECA prevents the mPTP opening through inactivation of GSK-3β via ERS inhibition. The cGMP/PKG signaling pathway is responsible for GSK-3β inactivation by NECA.

Astaxanthin supplementation attenuates immobilization-induced skeletal muscle fibrosis via suppression of oxidative stress

Immobilization induces skeletal muscle fibrosis characterized by increasing collagen synthesis in the perimysium and endomysium. Transforming growth factor-β1 (TGF-β1) is associated with this lesion via promoting differentiation of fibroblasts into myofibroblasts. In addition, reactive oxygen species (ROS) are shown to mediate TGF-β1-induced fibrosis in tissues. These reports suggest the importance of ROS reduction for attenuating skeletal muscle fibrosis. Astaxanthin, a powerful antioxidant, has been shown to reduce ROS production in disused muscle. Therefore, we investigated the effects of astaxanthin supplementation on muscle fibrosis under immobilization. In the present study, immobilization increased the collagen fiber area, the expression levels of TGF-β1, α-smooth muscle actin, and superoxide dismutase-1 protein and ROS production. However, these changes induced by immobilization were attenuated by astaxanthin supplementation. These results indicate the effectiveness of astaxanthin supplementation on skeletal muscle fibrosis induced by ankle joint immobilization.

Effect of Shenmai injection on preventing the development of nitroglycerin-induced tolerance in rats

Long-term nitroglycerin (NTG) therapy causes tolerance to its effects attributing to increased oxidative stress and endothelial dysfunction. Shenmai injection (SMI), which is clinically used to treat cardiovascular diseases, consists of two herbal medicines, Ginseng Rubra and Ophiopogonjaponicas, and is reported to have antioxidant effects. The present study was designed to investigate the potential preventive effects of Shenmai injection on development of nitroglycerin-induced tolerance. The present study involves both in vivo and in vitro experiments to investigate nitroglycerin-induced tolerance. We examined the effect of Shenmai injection on the cardiovascular oxidative stress by measuring the serum levels of malondialdehyde (MDA) and superoxide dismutase (SOD). Endothelial dysfunction was determined by an endothelium-dependent vasorelaxation method in aortic rings and NOS activity. Inhibition of the cGMP/cGK-I signalling pathway was determined from released serum levels of cGMP and the protein expression levels of sGC, cGK-I, PDE1A and P-VASP by western blot. Here, we showed that SMI ameliorated the decrease in AV Peak Vel, the attenuation in the vasodilation response to nitroglycerin and endothelial dysfunction. SMI also reduced the cardiovascular oxidative stress by reducing the release of MDA and increasing the activity of SOD. Shenmai injection further ameliorated inhibition of the cGMP/cGK-I signalling pathway triggered by nitroglycerin-induced tolerance through up-regulating the protein expression of sGC, cGK-I, and P-VASP and down- regulating the proteins expression of PDE1A. In vitro studies showed that Shenmai injection could recover the attenuated vasodilation response to nitroglycerin following incubation (of aortic rings) with nitroglycerin via activating the enzymes of sGC and cGK-I. Therefore, we conclude that Shenmai injection could prevent NTG nitroglycerin-induced tolerance at least in part by decreasing the cardiovascular oxidative stress, meliorating the endothelial dysfunction and ameliorating the inhibition of the cGMP/cGK-I signalling pathway. These findings indicate the potential of Shenmai injection (SMI) as a promising medicine for preventing the development of nitroglycerin-induced tolerance.

Serelaxin Treatment Reduces Oxidative Stress and Increases Aldehyde Dehydrogenase-2 to Attenuate Nitrate Tolerance

Background: Glyceryl trinitrate (GTN) is a commonly prescribed treatment for acute heart failure patients. However, prolonged GTN treatment induces tolerance, largely due to increased oxidative stress and reduced aldehyde dehydrogenase-2 (ALDH-2) expression. Serelaxin has several vasoprotective properties, which include reducing oxidative stress and augmenting endothelial function. We therefore tested the hypothesis in rodents that serelaxin treatment could attenuate low-dose GTN-induced tolerance.

Methods and Results: Co-incubation of mouse aortic rings ex vivo with GTN (10 μM) and serelaxin (10 nM) for 1 h, restored GTN responses, suggesting that serelaxin prevented the development of GTN tolerance. Male Wistar rats were subcutaneously infused with ethanol (control), low-dose GTN+placebo or low-dose GTN+serelaxin via osmotic minipumps for 3 days. Aortic vascular function and superoxide levels were assessed using wire myography and lucigenin-enhanced chemiluminescence assay respectively. Changes in aortic ALDH-2 expression were measured by qPCR and Western blot respectively. GTN+placebo infusion significantly increased superoxide levels, decreased ALDH-2 and attenuated GTN-mediated vascular relaxation. Serelaxin co-treatment with GTN significantly enhanced GTN-mediated vascular relaxation, reduced superoxide levels and increased ALDH-2 expression compared to GTN+placebo-treated rats.

Conclusion: Our data demonstrate that a combination of serelaxin treatment with low dose GTN attenuates the development of GTN-induced tolerance by reducing superoxide production and increasing ALDH-2 expression in the rat aorta. We suggest that serelaxin may improve nitrate efficacy in a clinical setting.

Muscles Susceptibility to Ischemia-Reperfusion Injuries Depends on Fiber Type Specific Antioxidant Level

Muscle injury resulting from ischemia-reperfusion largely aggravates patient prognosis but whether and how muscle phenotype modulates ischemia-reperfusion-induced mitochondrial dysfunction remains to be investigated. We challenged the hypothesis that glycolytic muscles are more prone to ischemia-reperfusion-induced injury than oxidative skeletal muscles. We therefore determined simultaneously the effect of 3 h of ischemia induced by aortic clamping followed by 2 h of reperfusion (IR, n = 11) on both gastrocnemius and soleus muscles, as compared to control animals (C, n = 11). Further, we investigated whether tempol, an antioxidant mimicking superoxide dismutase, might compensate a reduced defense system, likely characterizing glycolytic muscles (IR-Tempol, n = 7). In the glycolytic gastrocnemius muscle, as compared to control, ischemia-reperfusion significantly decreased mitochondrial respiration (-30.28 ± 6.16%, p = 0.003), increased reactive oxygen species production (+79.15 ± 28.72%, p = 0.04), and decreased reduced glutathione (-28.19 ± 6.80%, p = 0.011). Less deleterious effects were observed in the oxidative soleus muscle (-6.44 ± 6.30%, +4.32 ± 16.84%, and -8.07 ± 10.84%, respectively), characterized by enhanced antioxidant defenses (0.63 ± 0.05 in gastrocnemius vs. 1.24 ± 0.08 μmol L^-1 g^-1 in soleus). Further, when previously treated with tempol, glycolytic muscle was largely protected against the deleterious effects of ischemia-reperfusion. Thus, oxidative skeletal muscles are more protected than glycolytic ones against ischemia-reperfusion, thanks to their antioxidant pool. Such pivotal data support that susceptibility to ischemia-reperfusion-induced injury differs between organs, depending on their metabolic phenotypes. This suggests a need to adapt therapeutic strategies to the specific antioxidant power of the target organ to be protected.

The Role of Reactive Oxygen and Nitrogen Species in the Expression and Splicing of Nitric Oxide Receptor

SIGNIFICANCE

Nitric oxide (NO)-dependent signaling is critical to many cellular functions and physiological processes. Soluble guanylyl cyclase (sGC) acts as an NO receptor and mediates the majority of NO functions. The signaling between NO and sGC is strongly altered by reactive oxygen and nitrogen species. Recent Advances: Besides NO scavenging, sGC is affected by oxidation/loss of sGC heme, oxidation, or nitrosation of cysteine residues and phosphorylation. Apo-sGC or sGC containing oxidized heme is targeted for degradation. sGC transcription and the stability of sGC mRNA are also affected by oxidative stress.

CRITICAL ISSUES

Studies cited in this review suggest the existence of compensatory processes that adapt cellular processes to diminished sGC function under conditions of short-term or moderate oxidative stress. Alternative splicing of sGC transcripts is discussed as a mechanism with the potential to both enhance and reduce sGC function. The expression of α1 isoform B, a functional and stable splice variant of human α1 sGC subunit, is proposed as one of such compensatory mechanisms. The expression of dysfunctional splice isoforms is discussed as a contributor to decreased sGC function in vascular disease.

FUTURE DIRECTIONS

Targeting the process of sGC splicing may be an important approach to maintain the composition of sGC transcripts that are expressed in healthy tissues under normal conditions. Emerging new strategies that allow for targeted manipulations of RNA splicing offer opportunities to use this approach as a preventive measure and to control the composition of sGC splice isoforms. Rational management of expressed sGC splice forms may be a valuable complementary treatment strategy for existing sGC-directed therapies. Antioxid. Redox Signal. 26, 122-136.

The Microbiology of Ruthenium Complexes

Ruthenium is seldom mentioned in microbiology texts, due to the fact that this metal has no known, essential roles in biological systems, nor is it generally considered toxic. Since the fortuitous discovery of cisplatin, first as an antimicrobial agent and then later employed widely as an anticancer agent, complexes of other platinum group metals, such as ruthenium, have attracted interest for their medicinal properties. Here, we review at length how ruthenium complexes have been investigated as potential antimicrobial, antiparasitic and chemotherapeutic agents, in addition to their long and well-established roles as biological stains and inhibitors of calcium channels. Ruthenium complexes are also employed in a surprising number of biotechnological roles. It is in the employment of ruthenium complexes as antimicrobial agents and alternatives or adjuvants to more traditional antibiotics, that we expect to see the most striking developments in the future. Such novel contributions from organometallic chemistry are undoubtedly sorely needed to address the antimicrobial resistance crisis and the slow appearance on the market of new antibiotics.

Effect of calcitonin gene-related peptide antagonist on the cardiovascular events, mortality, and prostaglandin E2 production by nitrate-induced tolerant rats with acute myocardial infarction

Background

Anti-ischemic effects of NO releasing by nitroglycerin (NTG) and the release of calcitonin gene-related peptide (CGRP) are involved in the decrease of vascular remodeling in different cardiovascular diseases. Using a nitrate-free period is still generally required to prevent nitrate tolerance and should be used as the first-line option to maintain adequate symptom control and on an individual basis. Personalized anti-ischemic concerns require the urgent change of paradigm from interventional measures to predictive, preventive, and personalized treatment with organic nitrates and its combination with drugs that may improve prognosis and drugs that can be added for patients who remain symptomatic despite therapy with the other classes of agents. The purpose of this study was to evaluate the influence of human calcitonin gene-related peptide antagonist (CGRP_8-37) on cardiohemodynamic events, prostaglandin E₂ (PGE₂) plasma concentration, the severity of ventricular arrhythmias, and mortality occurring during acute myocardial infarction (AMI) in NTG-tolerant and nontolerant rats.

Methods

In the pilot study of efficacy of calcitonin gene-related peptide antagonist (CGRP_8-37), 58 male Wistar rats were included. All procedures were performed according to protocols approved by the General Animal Care and Use Committee. Adult male rats underwent surgery to induce AMI by ligating the left anterior descending coronary artery or SHAM. ECG was used to confirm myocardial ischemia. In each experiment, a rat was maintained under anesthesia for the duration of the experiment. At the end of the experiment, the rat was killed by an overdose of pentobarbital. All animals in accordance with the received pharmacological agent were randomized into three groups: I—received only NTG, 50 mg/kg daily, s.c. injections b.i.d. 3 days prior to AMI; II—received NTG by the same dose, route, and frequency of administration + CGRP antagonist (CGRP_8-37), 10 μg/kg two times daily by a similar period of administration; and III—served as control (C) group without preliminary tolerance to NTG.

Results

Subcutaneous injections of NTG (50 mg/kg) 30 min prior to AMI in NTG-tolerant animals (group I) and in NTG-tolerant rats + CGRP antagonist (group II) caused minor changes in blood pressure and heart period that was accompanied before NTG s.c. administration with blunted baroreflex sensitivity in response to i.v. administration of sodium nitroprusside in these groups of rats (0.66 ± 0.05 and 0.56 ± 0.04 ms/mmHg, P < 0.05, respectively) in comparison to C (group III) animals (0.9 ± 0.1 ms/mmHg). AMI 1 h duration was associated with a high incidence of ventricular arrhythmia and significant mortality in group I (70 %) and especially in group II (90 %) animals at 72 h after reperfusion as compared with group III rats (56 %), that correlated to a decrease of PGE₂ plasma content in group II (2.2 ± 0.4 ng/ml, P < 0.001) and group I (3.6 ± 0.2 ng/ml, P < 0.01) vs. control group of rats (4.8 ± 0.3 ng/ml).

Conclusions

CGRP could be involved in the mechanism of nitrate tolerance via the inhibition of release of the potent vasodilator CGRP leading to exacerbation of acute myocardial ischemia. The influence of CGRP antagonist could enhance this condition.

Organic Nitrate Therapy, Nitrate Tolerance, and Nitrate-Induced Endothelial Dysfunction: Emphasis on Redox Biology and Oxidative Stress

Organic nitrates, such as nitroglycerin (GTN), isosorbide-5-mononitrate and isosorbide dinitrate, and pentaerithrityl tetranitrate (PETN), when given acutely, have potent vasodilator effects improving symptoms in patients with acute and chronic congestive heart failure, stable coronary artery disease, acute coronary syndromes, or arterial hypertension. The mechanisms underlying vasodilation include the release of •NO or a related compound in response to intracellular bioactivation (for GTN, the mitochondrial aldehyde dehydrogenase [ALDH-2]) and activation of the enzyme, soluble guanylyl cyclase. Increasing cyclic guanosine-3',-5'-monophosphate (cGMP) levels lead to an activation of the cGMP-dependent kinase I, thereby causing the relaxation of the vascular smooth muscle by decreasing intracellular calcium concentrations. The hemodynamic and anti-ischemic effects of organic nitrates are rapidly lost upon long-term (low-dose) administration due to the rapid development of tolerance and endothelial dysfunction, which is in most cases linked to increased intracellular oxidative stress. Enzymatic sources of reactive oxygen species under nitrate therapy include mitochondria, NADPH oxidases, and an uncoupled •NO synthase. Acute high-dose challenges with organic nitrates cause a similar loss of potency (tachyphylaxis), but with distinct pathomechanism. The differences among organic nitrates are highlighted regarding their potency to induce oxidative stress and subsequent tolerance and endothelial dysfunction. We also address pleiotropic effects of organic nitrates, for example, their capacity to stimulate antioxidant pathways like those demonstrated for PETN, all of which may prevent adverse effects in response to long-term therapy. Based on these considerations, we will discuss and present some preclinical data on how the nitrate of the future should be designed.

Phosphodiesterase-5 inhibitor tadalafil attenuates oxidative stress and protects against myocardial ischemia/reperfusion injury in type 2 diabetic mice

Diabetic patients exhibit increased risk for the development of cardiovascular diseases primarily because of impaired nitric oxide (NO) bioavailability. The phosphodiesterase-5 (PDE-5) inhibitor sildenafil restores NO signaling and protects against ischemia/reperfusion (I/R) injury. In this study, we determined the effect of the long-acting PDE-5 inhibitor tadalafil on diabetes-associated complications and its role in attenuating oxidative stress after I/R injury in type 2 diabetic db/db mice. Adult male db/db mice (n=40/group) were randomized to receive dimethyl sulfoxide (10% DMSO, 0.2ml, ip) or tadalafil (1mg/kg in 10% DMSO, ip) for 28 days. After 28 days treatment, the hearts were isolated and subjected to 30min global ischemia followed by 60min reperfusion in the Langendorff mode. Infarct size was measured using computer morphometry of tetrazolium-stained sections. Cardiomyocytes were isolated from a subset of hearts and subjected to 40min simulated ischemia followed by 1h of reoxygenation (SI/RO). Dichlorodihydrofluorescein diacetate and JC-1 staining was used to measure reactive oxygen species (ROS) generation and mitochondrial membrane potential (Δψm), respectively. Another subset of hearts was used for the estimation of lipid peroxidation, glutathione, and the expression of myocardial pRac1, Rac1, gp91(phox), p47(phox), and p67(phox) by Western blot. Tadalafil treatment improved the metabolic status and reduced infarct size compared to the untreated db/db mice (21.2±1.8% vs 45.8±2.8%; p<0.01). The db/db mice showed enhanced oxidative stress in cardiomyocytes as indicated by a significant increase in ROS production. Cardiac NAD(P)H oxidase activity, lipid peroxidation, and oxidized glutathione were also increased in db/db mice compared to nondiabetic control animals. Tadalafil treatment in db/db mice suppressed oxidative stress, attenuated myocardial expression of pRac1 and gp91(phox), and also preserved the loss of Δψm in cardiomyocytes after SI/RO. In conclusion, these results demonstrate that chronic treatment with tadalafil attenuates oxidative stress and improves mitochondrial integrity while providing powerful cardioprotective effects in type 2 diabetes.

Cyclosporine A normalizes mitochondrial coupling, reactive oxygen species production, and inflammation and partially restores skeletal muscle maximal oxidative capacity in experimental aortic cross-clamping

OBJECTIVE

By binding to cyclophilin D, cyclosporine A (CsA) inhibits mitochondrial permeability transition pore (mPTP) opening and prevents mitochondrial dysfunction and ultimately cell death after ischemia-reperfusion (IR) injury in cardiac muscle. This study tested whether CsA would decrease skeletal muscle oxidative stress and mitochondrial dysfunctions after aortic cross-clamping related IR.

METHODS

Forty-five Wistar rats were investigated. The sham group (n = 8) had aortic exposure but no ischemia, the IR group (n = 10) had aortic cross-clamping for 3 hours followed by 2 hours of reperfusion, and the IR+CsA group (n = 9) had two intraperitoneal injections of 10 mg of CsA at 90 and 150 minutes of ischemia before reperfusion. Mitochondrial coupling (acceptor control ratio) and mitochondrial respiratory chain complexes' activities were measured. Reactive oxygen species (ROS) production, cyclophilin D expression, and muscle inflammation were determined using dihydroethidium staining, Western blot, and immunohistochemistry, respectively. An additional 18 sham rats were investigated to determine CsA blood levels and the effects of CsA on mitochondrial respiration and calcium retention capacity, a marker of mPTP opening, both in myocardium and gastrocnemius with and without CsA.

RESULTS

Compared with sham, IR decreased mitochondrial coupling (1.38 ± 0.06 vs 1.98 ± 0.20; P = .0092), increased ROS production (3992 ± 706 arbitrary units [AU] vs 1812 ± 322 AU; P = .033), was associated with macrophage infiltration, and decreased maximal oxidative capacity (V(max): 4.08 ± 0.38 μmol O(2)/min/g vs 5.98 ± 0.56 μmol O(2)/min/g; P = .015). Despite IR, CsA treatment totally restored mitochondrial coupling (1.93 ± 0.12; P = .023 vs IR), normalized ROS (1569 ± 348 AU; P = .0098 vs IR), and decreased inflammation. The V(max) was slightly enhanced (5.02 ± 0.39 μmol O(2)/min/g; P = .33 vs IR; P = .35 vs sham). Compared with myocardium, gastrocnemius muscle was characterized by a decreased cyclophilin D content (-50%) associated with an earlier opening of mPTP (calcium retention capacity increased from 10.85 ± 1.35 μM/mg dry weight [DW] to 12.11 ± 2.77 μM/mg DW; P = .65; and from 11.07 ± 1.67 to 37.65 ± 11.41 μM/mg DW; P = .0098 in gastrocnemius and heart, respectively).

CONCLUSIONS

Cyclosporine A normalized ROS production, decreased inflammation, and restored mitochondrial coupling during aortic cross-clamping. Incomplete Vmax protection might be due to low cyclophilin D expression in gastrocnemius, preventing CsA from blocking mPTP opening.

Pretreatment with brain natriuretic peptide reduces skeletal muscle mitochondrial dysfunction and oxidative stress after ischemia-reperfusion

Brain natriuretic peptide (BNP) reduces the extent of myocardial infarction. We aimed to determine whether BNP may reduce skeletal muscle mitochondrial dysfunctions and oxidative stress through mitochondrial K(ATP) (mK(ATP)) channel opening after ischemia-reperfusion (IR). Wistar rats were assigned to four groups: sham, 3-h leg ischemia followed by 2-h reperfusion (IR), pretreatment with BNP, and pretreatment with 5-hydroxydecanoic acid, an mK(ATP) channel blocker, before BNP. Mitochondrial respiratory chain complex activities of gastrocnemius muscles were determined using glutamate-malate (V(max)), succinate (V(succ)), and N,N,N',N'-tetramethyl-p-phenylenediamine dihydrochloride ascorbate (V(TMPD/asc)). Apoptosis (Bax-to-Bcl2 mRNA ratio and caspase-3 activity) and oxidative stress (dihydroethidium staining) were also assessed. Compared with the sham group, IR significantly decreased V(max), reflecting complex I, II, and IV activities (-36%, 3.7 ± 0.3 vs. 5.8 ± 0.2 μmol O(2)·min(-1)·g dry wt(-1), P < 0.01), and V(TMPD/asc), reflecting complex IV activity (-37%, 8.6 ± 0.8 vs. 13.7 ± 0.9 μmol O(2)·min(-1)·g dry wt(-1), P < 0.01). IR increased Bax-to-Bcl2 ratio (+57%, 1.1 ± 0.1 vs. 0.7 ± 0.1, P < 0.05) and oxidative stress (+45%, 9,067 ± 935 vs. 6,249 ± 723 pixels, P > 0.05). BNP pretreatment reduced the above alterations, increasing V(max) (+38%, P < 0.05) and reducing Bax-to-Bcl2 ratio (-55%, P < 0.01) and oxidative stress (-58%, P < 0.01). BNP protection against deleterious IR effects on skeletal muscles was abolished by 5-hydroxydecanoic acid. Caspase-3 activities did not change significantly. Conversely, BNP injected during ischemia failed to protect against muscle injury. In addition to maintaining the activity of mitochondrial respiratory chain complexes and possibly decreasing apoptosis, pretreatment with BNP protects skeletal muscle against IR-induced lesions, most likely by decreasing excessive production of radical oxygen species and opening mK(ATP) channels.

Evidence for a relationship between mitochondrial Complex I activity and mitochondrial aldehyde dehydrogenase during nitroglycerin tolerance: effects of mitochondrial antioxidants

The medical use of nitroglycerin (GTN) is limited by patient tolerance. The present study evaluated the role of mitochondrial Complex I in GTN biotransformation and the therapeutic effect of mitochondrial antioxidants. The development of GTN tolerance (in rat and human vessels) produced a decrease in mitochondrial O(2) consumption. Co-incubation with the mitochondria-targeted antioxidant mitoquinone (MQ, 10(-6)mol/L) or with glutathione ester (GEE, 10(-4)mol/L) blocked GTN tolerance and the effects of GTN on mitochondrial respiration and aldehyde dehydrogenase 2 (ALDH-2) activity. Biotransformation of GTN depended on the mitochondria being functionally active, particularly mitochondrial Complex I. Tolerance induced mitochondrial ROS production and oxidative stress, though these effects were not detected in HUVECρ(0) cells or Complex I mutant cells. Experiments performed to evaluate Complex I-dependent respiration demonstrated that its inhibition by GTN was prevented by the antioxidants in control samples. These results point to a key role for mitochondrial Complex I in the adequate functioning of ALDH-2. In addition, we have identified mitochondrial Complex I as one of the targets at which the initial oxidative stress responsible for GTN tolerance takes place. Our data also suggest a role for mitochondrial-antioxidants as therapeutic tools in the control of the tolerance that accompanies chronic nitrate use.

Nitroglycerin use in myocardial infarction patients

Acute myocardial infarction (MI) and its sequelae are leading causes of morbidity and mortality worldwide. Nitroglycerin (glyceryl trinitrate [GTN]) remains a first-line treatment for angina pectoris and acute MI. Nitroglycerin achieves its benefit by giving rise to nitric oxide (NO), which causes vasodilation and increases blood flow to the myocardium. However, continuous delivery of GTN results in tolerance, limiting the use of this drug. Nitroglycerin tolerance is caused, at least in part, by inactivation of aldehyde dehydrogenase 2 (ALDH2), an enzyme that converts GTN to the vasodilator, NO. We recently found that in a MI model in animals, in addition to GTN's effect on the vasculature, sustained treatment negatively affected cardiomyocyte viability following ischemia, thus resulting in increased infarct size. Coadministration of Alda-1, an activator of ALDH2, with GTN improves metabolism of reactive aldehyde adducts and prevents the GTN-induced increase in cardiac dysfunction following MI. In this review, we describe the molecular mechanisms associated with the benefits and risks of GTN administration in MI.

Atorvastatin treatment reduces exercise capacities in rats: involvement of mitochondrial impairments and oxidative stress

Physical exercise exacerbates the cytotoxic effects of statins in skeletal muscle. Mitochondrial impairments may play an important role in the development of muscular symptoms following statin treatment. Our objective was to characterize mitochondrial function and reactive oxygen species (ROS) production in skeletal muscle after exhaustive exercise in atorvastatin-treated rats. The animals were divided into four groups: resting control (CONT; n = 8) and exercise rats (CONT+EXE; n = 8) as well as resting (ATO; n = 10) and exercise (ATO+EXE; n = 8) rats that were treated with atorvastatin (10 mg·kg(-1)·day(-1) for 2 wk). Exhaustive exercise showed that the distance that was covered by treated animals was reduced (P < 0.05). Using dihydroethidium staining, we showed that the ROS level was increased by 60% in the plantaris muscle of ATO compared with CONT rats and was highly increased in ATO+EXE (226%) compared with that in CONT+EXE rats. The maximal mitochondrial respiration (V(max)) was decreased in ATO rats compared with that in CONT rats (P < 0.01). In CONT+EXE rats, V(max) significantly increased compared with those in CONT rats (P < 0.05). V(max) was significantly lower in ATO+EXE rats (-39%) compared with that in CONT+EXE rats (P < 0.001). The distance that was covered by rats significantly correlated with V(max) (r = 0.62, P < 0.01). The glycogen content was decreased in ATO, CONT+EXE, and ATO+EXE rats compared with that in CONT rats (P < 0.05). GLUT-4 mRNA expression was higher after exhaustive exercise in CONT+EXE rats compared with the other groups (P < 0.05). Our results show that exhaustive exercise exacerbated metabolic perturbations and ROS production in skeletal muscle, which may reduce the exercise capacity and promote the muscular symptoms in sedentary atorvastatin-treated animals.

RNA splicing in regulation of nitric oxide receptor soluble guanylyl cyclase

Soluble guanylyl cyclase (sGC) is a key protein in the nitric oxide (NO)/-cGMP signaling pathway. sGC activity is involved in a number of important physiological processes including smooth muscle relaxation, neurotransmission and platelet aggregation and adhesion. Regulation of sGC expression and activity emerges as a crucial factor in control of sGC function in normal and pathological conditions. Recently accumulated evidence strongly indicates that the regulation of sGC expression is a complex process modulated on several levels including transcription, post-transcriptional regulation, translation and protein stability. Presently our understanding of mechanisms governing regulation of sGC expression remains very limited and awaits systematic investigation. Among other ways, the expression of sGC subunits is modulated at the levels of mRNA abundance and transcript diversity. In this review we summarize available information on different mechanisms (including transcriptional activation, mRNA stability and alternative splicing) involved in the modulation of mRNA levels of sGC subunits in response to various environmental clues. We also summarize and cross-reference the information on human sGC splice forms available in the literature and in genomic databases. This review highlights the fact that the study of the biological role and regulation of sGC splicing will bring new insights to our understanding of NO/cGMP biology.

Chronic administration of the HNO donor Angeli's salt does not lead to tolerance, cross-tolerance, or endothelial dysfunction: comparison with GTN and DEA/NO

Nitroxyl (HNO) displays distinct pharmacology to its redox congener nitric oxide (NO(•)) with therapeutic potential in the treatment of heart failure. It remains unknown if HNO donors are resistant to tolerance development following chronic in vivo administration. Wistar-Kyoto rats received a 3-day subcutaneous infusion of one of the NO(•) donors, glyceryl trinitrate (GTN) or diethylamine/NONOate (DEA/NO), or the HNO donor Angeli's salt (AS). GTN infusion (10 μg/kg/min) resulted in significantly blunted depressor responses to intravenous bolus doses of GTN, demonstrating tolerance development. By contrast, infusion with AS (20 μg/kg/min) or DEA/NO (2 μg/kg/min) did not alter their subsequent depressor responses. Similarly, ex vivo vasorelaxation responses in isolated aortae revealed that GTN infusion elicited a significant 6-fold decrease in the sensitivity to GTN and reduction in the maximum response to acetylcholine (ACh). Chronic infusion of AS or DEA/NO had no effect on subsequent vasorelaxation responses to themselves or to ACh. No functional cross-tolerance between nitrovasodilators was evident, either in vivo or ex vivo, although an impaired ability of a nitrovasodilator to increase tissue cGMP content was not necessarily indicative of a reduced functional response. In conclusion, HNO donors may represent novel therapies for cardiovascular disease with therapeutic potential over clinically used organic nitrates.

Severe obesity is associated with impaired arterial smooth muscle function in young adults

The degree of arterial dilatation induced by exogenous nitrates (nitrate-mediated dilatation, NMD) has been similar in obese and normal-weight adults after single high-dose glyceryl trinitrate (GTN). We examined whether NMD is impaired in obesity by performing a GTN dose-response study, as this is a potentially more sensitive measure of arterial smooth muscle function. In this cross-sectional study, subjects were 19 obese (age 31.0 ± 1.2 years, 10 male, BMI 44.1 ± 2.1) and 19 age- and sex-matched normal-weight (BMI 22.4 ± 0.4) young adults. Blood pressure (BP), triglycerides, high-density lipoprotein (HDL), and low-density lipoprotein (LDL)-cholesterol, glucose, insulin, high-sensitivity C-reactive protein (hs-CRP), carotid intima-media thickness (CIMT), and flow-mediated dilatation (FMD) were measured. After incremental doses of GTN, brachial artery maximal percent dilatation (maximal NMD) and the area under the dose-response curve (NMD AUC) were calculated. Maximal NMD (13.4 ± 0.9% vs. 18.3 ± 1.1%, P = 0.002) and NMD AUC (54,316 ± 362 vs. 55,613 ± 375, P = 0.018) were lower in obese subjects. The obese had significantly higher hs-CRP, insulin, and CIMT and lower HDL-cholesterol. Significant bivariate associations existed between maximal NMD or NMD AUC and BMI-group (r = -0.492, P = 0.001 or r = -0.383, P = 0.009), hs-CRP (r = -0.419, P = 0.004 or r = -0.351, P = 0.015), and HDL-cholesterol (r = 0.374, P = 0.01 or r = 0.270, P = 0.05). On multivariate analysis, higher BMI-group remained as the only significant determinant of maximal NMD (r² = 0.242, β = -0.492, P = 0.002) and NMD AUC (r² = 0.147, β = -0.383, P = 0.023). In conclusion, arterial smooth muscle function is significantly impaired in the obese. This may be important in their increased cardiovascular risk.

Hypoxia inducible factor-1 protects against nitrate tolerance and stunning in rabbit cardiac myocytes

PURPOSE

We tested whether upregulation of hypoxia inducible factor-1 (HIF-1) would restore the blunted effects of natriuretic peptides and nitric oxide caused by chronic nitrate exposure and stunning in cardiac myocytes.

METHODS

HIF-1alpha was increased with deferoxamine (150 mg/kg for 2 days). Nitrate tolerance was induced by a chronic nitroglycerin patch (0.3 mg/h for 5 days). We used freshly isolated rabbit ventricular myocytes. Half the myocytes were subjected to simulated ischemia [15 min 95% N(2)-5% CO(2)] and reperfusion [reoxygenation] to produce stunning. Cell function was measured utilizing a video-edge detector. Shortening was examined at baseline and after brain natriuretic peptide (BNP, 10(-8), 10(-7) M) or S-nitroso-N-acetyl-penicillamine (SNAP, 10(-6), 10(-5) M) followed by KT5823 (cyclic GMP protein kinase inhibitor, 10(-6) M). We also measured cyclic GMP protein kinase protein levels and kinase activity.

RESULTS

In control, BNP (-29%) reduced percent shortening, while KT5823 partially restored function. Deferoxamine treated control myocytes responded similarly. In patched nonstunned myocytes, BNP (-12%) reduced shortening less and KT5823 did not increase function. However, deferoxamine restored the blunted effects of BNP (-21%) and KT5823. In stunned myocytes, BNP (-11%) reduced shortening less and KT5823 did not affect function. Deferoxamine increased the effects of BNP (-27%) and KT5823 in stunning. Patch combined with stunning also similarly blunted the effects of BNP (-12%) and KT5823. Deferoxamine improved the effects of BNP (-22%) and KT5823. Similar results were observed after SNAP. Stunning reduced cyclic GMP protein kinase activity and deferoxamine restored activity. Deferoxamine had no effect on kinase activity in nitrate tolerance.

CONCLUSION

We found that upregulation of HIF-1 could protect isolated cardiac myocytes against nitrate tolerance through a cyclic GMP protein kinase-independent mechanism and through a kinase-dependent mechanism in stunning.

Coadministration of carvedilol attenuates nitrate tolerance by preventing cytochrome p450 depletion

BACKGROUND

Long-term administration of nitroglycerin (NTG) causes tolerance secondary to increased vascular formation of reactive oxygen species. Carvedilol, which has potent antioxidant activity in addition to functioning as an adrenergic blocker, prevents nitrate tolerance by a still to be elucidated mechanism. The present study investigated how carvedilol attenuates nitrate tolerance, particularly with reference to cytochrome P450 (CYP), an enzyme involved in the development of tolerance.

METHODS AND RESULTS

Male Wistar rats were subjected to 48-h continuous infusion of NTG alone (0.5 mg/h) or NTG with concomitant carvedilol (20 or 100 microg/h), and then compared with vehicle-treated rats (4 groups; n=6 in each group). Following the continuous administration, nitrate tolerance, assessed by bolus NTG injections, was hemodynamically prevented by coadministration of carvedilol. Levels of CYP1A1/1A2, superoxide production, and phosphorylated vasodilator-stimulated phosphoprotein at serine 239 (P-VASP) were examined in the aortic wall and heart tissue. When NTG alone was continuously administered, vascular superoxide was produced, there was a decrease in the cardiac CYP1A1/1A2 level, and depletion of P-VASP. However, each of these changes induced by continuous NTG administration was significantly attenuated by coadministration of carvedilol and the extent of attenuation was more pronounced at the higher dose (100 microg/h).

CONCLUSIONS

Coadministration of carvedilol attenuates nitrate tolerance through maintenance of NO/cGMP pathway activity by preventing free radical generation and CYP depletion.

Redox signaling (cross-talk) from and to mitochondria involves mitochondrial pores and reactive oxygen species

This review highlights the important role of redox signaling between mitochondria and NADPH oxidases. Besides the definition and general importance of redox signaling, the cross-talk between mitochondrial and Nox-derived reactive oxygen species (ROS) is discussed on the basis of 4 different examples. In the first model, angiotensin-II is discussed as a trigger for NADPH oxidase activation with subsequent ROS-dependent opening of mitochondrial ATP-sensitive potassium channels leading to depolarization of mitochondrial membrane potential followed by mitochondrial ROS formation and respiratory dysfunction. This concept was supported by observations that ethidium bromide-induced mitochondrial damage suppressed angiotensin-II-dependent increase in Nox1 and oxidative stress. In another example hypoxia was used as a stimulator of mitochondrial ROS formation and by using pharmacological and genetic inhibitors, a role of mitochondrial ROS for the induction of NADPH oxidase via PKCvarepsilon was demonstrated. The third model was based on cell death by serum withdrawal that promotes the production of ROS in human 293T cells by stimulating both the mitochondria and Nox1. By superior molecular biological methods the authors showed that mitochondria were responsible for the fast onset of ROS formation followed by a slower but long-lasting oxidative stress condition based on the activation of an NADPH oxidase (Nox1) in response to the fast mitochondrial ROS formation. Finally, a cross-talk between mitochondria and NADPH oxidases (Nox2) was shown in nitroglycerin-induced tolerance involving the mitochondrial permeability transition pore and ATP-sensitive potassium channels. The use of these redox signaling pathways as pharmacological targets is briefly discussed.

Organic nitrates and nitrate tolerance--state of the art and future developments

The hemodynamic and antiischemic effects of nitroglycerin (GTN) are lost upon chronic administration due to the rapid development of nitrate tolerance. The mechanism of this phenomenon has puzzled several generations of scientists, but recent findings have led to novel hypotheses. The formation of reactive oxygen and nitrogen species in the mitochondria and the subsequent inhibition of the nitrate-bioactivating enzyme mitochondrial aldehyde dehydrogenase (ALDH-2) appear to play a central role, at least for GTN, that is, bioactivated by ALDH-2. Importantly, these findings provide the opportunity to reconcile the two "traditional" hypotheses of nitrate tolerance, that is, the one postulating a decreased bioactivation and the concurrent one suggesting a role of oxidative stress. Furthermore, recent animal and human experimental studies suggest that the organic nitrates are not a homogeneous group but demonstrate a broad diversity with regard to induction of vascular dysfunction, oxidative stress, and other side effects. In the past, attempts to avoid nitrate-induced side effects have focused on administration schedules that would allow a "nitrate-free interval"; in the future, the role of co-therapies with antioxidant compounds and of activation of endogeneous protective pathways such as the heme oxygenase 1 (HO-1) will need to be explored. However, the development of new nitrates, for example, tolerance-free aminoalkyl nitrates or combination of nitrate groups with established cardiovascular drugs like ACE inhibitors or AT(1)-receptor blockers (hybrid molecules) may be of great clinical interest.

Degradation of leucine zipper-positive isoform of MYPT1 may contribute to development of nitrate tolerance

AIMS

A depressed cGMP-dependent protein kinase (PKG) activity is implicated in nitrate tolerance. The present study determines whether the leucine zipper-positive (LZ+) isoform of myosin phosphatase target subunit 1 (MYPT1), a key target protein for PKG actions, is involved in the development of nitrate tolerance.

METHODS AND RESULTS

Nitrate tolerance in in vitro preparations was obtained by a 24 h incubation with nitroglycerin (NTG). Nitrate tolerance in in vivo preparations was obtained by subcutaneous injection of mice with NTG, and the aortas were used. Protein levels of total MYPT1, MYPT1 (LZ+), PP1Cdelta, myosin light chain (MLC), and phosphorylated MLC were determined by Western blot analysis. Isometric vessel tension was determined by an organ chamber technique. Protein levels of MYPT1 (LZ+), but not of PP1Cdelta, were significantly reduced in in vitro and in vivo nitrate-tolerant arteries. The decrease in the MYPT1 (LZ+) protein level of coronary artery was also induced by a nitric oxide donor and a cGMP analogue, which was prevented by the inhibitors of soluble guanylyl cyclase and PKG. The decrease in MYPT1 (LZ+) protein levels was not affected by the inhibitor of protein synthesis, but was prevented by the inhibitors of proteasomes. The diminished inhibition of dephosphorylation of MLC as well as the attenuated relaxation of porcine coronary artery and mouse aorta to NTG was improved by proteasome inhibitors.

CONCLUSION

This study demonstrates that a reduction in the protein level of MYPT1 (LZ+) is involved in nitrate tolerance. This may result in part from a proteasome-dependent degradation of MYPT1 (LZ+).

Lack of effect of norfloxacin on hyperdynamic circulation in bile duct-ligated rats despite reduction of endothelial nitric oxide synthase function: result of unchanged vascular Rho-kinase?

BACKGROUND/AIMS

In cirrhosis, portal hypertension is maintained by splanchnic vasodilation owing to overproduction of the vasodilator nitric oxide (NO) and defective contractile signalling by Rho-kinase. NO overproduction is partially caused by bacterial translocation from the gut to mesenteric lymph nodes. However, the effects of intestinal bacterial decontamination on hyperdynamic circulation or vascular contractility are unknown. We investigated the haemodynamic and vascular effects of norfloxacin in rats with secondary biliary cirrhosis.

METHODS

Cirrhosis was induced by bile duct ligation (BDL). One group was treated with norfloxacin (20 mg/kg/day, 5 days, orally). Bacterial growth in the lymph nodes was determined on blood agar plates. Invasive haemodynamic measurements were combined with coloured microspheres. Aortic contractility was assessed myographically. Protein expression/phosphorylation was examined by Western blot analysis.

RESULTS

Norfloxacin treatment of BDL rats abolished bacterial translocation to mesenteric lymph nodes. BDL rats had hyperdynamic circulation, including portal hypertension and splanchnic vasodilation. None of these parameters was changed by norfloxacin, although norfloxacin reduced endothelial NO synthase expression and phosphorylation. The latter was associated with a diminished activity of protein kinase G (PKG), which mediates NO-induced vasodilation. However, norfloxacin had no effect on aortic contractility to methoxamine or Ca2+, or the aortic expression of RhoA, Rho-kinase and beta-arrestin 2, or the phosphorylation of the Rho-kinase substrate moesin.

CONCLUSIONS

Short-term treatment of BDL rats with norfloxacin does not change hyperdynamic circulation or vascular contractility, despite reduction of PKG activity.

Effects of nitroglycerin or pentaerithrityl tetranitrate treatment on the gene expression in rat hearts: evidence for cardiotoxic and cardioprotective effects

Nitroglycerin (NTG) and pentaerithrityl tetranitrate (PETN) are organic nitrates used in the treatment of angina pectoris, myocardial infarction, and congestive heart failure. Recent data show marked differences in the effects of NTG and PETN on the generation of reactive oxygen species. These differences are attributed to different effects of NTG and PETN on the expression of antioxidative proteins like the heme oxygenase-I. To analyze the expressional effects of NTG and PETN in a more comprehensive manner we performed whole genome expression profiling experiments using cardiac total RNA from NTG- or PETN-treated rats and DNA microarrays containing oligonucleotides representing 27,044 rat gene transcripts. The data obtained show that NTG and PETN together significantly modify the expression of >1,600 genes (NTG 532, PETN 1212). However, the expression of only a small group of these genes (68) was modified by both treatments, indicating marked differences in the expressional effects of NTG and PETN. NTG treatment resulted in the enhanced expression of genes that are believed to be markers for cardiotoxic processes. In addition, NTG treatment reduced the expression of genes described to code for cardioprotective proteins. In sharp contrast, PETN treatment enhanced the expression of cardioprotective genes and reduced the expression of genes believed to perform cardiotoxic effects. In conclusion, our data suggest that NTG treatment results in the induction of cardiotoxic gene expression networks leading to an activation of mechanisms that result in pathological changes in cardiomyocytes. In contrast, PETN treatment seems to activate gene expression networks that result in cardioprotective effects.

Role of glutaredoxin-mediated protein S-glutathionylation in cellular nitroglycerin tolerance

We hypothesize that nitroglycerin (NTG) causes direct oxidation of multiple cellular sulfhydryl (SH) proteins and that manipulation of SH redox status affects NTG tolerance. In LLC-PK1 cells, we found that nitrate tolerance, as indicated by cGMP accumulation toward NTG, was accompanied by increased protein [(35)S]cysteine incorporation, significant S-glutathionylation of multiple proteins, and decreased metabolic activity of several SH-sensitive enzymes, including creatine kinase, xanthine oxidoreductase, and glutaredoxin (GRX). Cells overexpressing GRX exhibited reduced cellular protein S-glutathionylation (PSSG) and absence of NTG tolerance, whereas those with silenced GRX showed increased extent of NTG-induced tolerance. Incubation of LLC-PK1 cells with oxidized glutathione led to several major observations associated with nitrate tolerance, namely, reduced cGMP accumulation, PSSG formation, superoxide accumulation, and the attenuation of these events by vitamin C. Aortic S-glutathionylated proteins increased approximately 3-fold in rats made tolerant in vivo to NTG and showed significant negative correlation with vascular responsiveness ex vivo. NTG incubation in EA.hy926 endothelial cells and LLC-PK1 cells led to increased S-glutathionylation and activity of p21(ras), a known mediator of cellular signaling. These results indicate that the hallmark events of NTG tolerance, such as reduced bioactivation and redox signaling, are associated with GRX-dependent protein deglutathionylation.

NO-independent, haem-dependent soluble guanylate cyclase stimulators

The nitric oxide (NO) signalling pathway is altered in cardiovascular diseases, including systemic and pulmonary hypertension, stroke, and atherosclerosis. The vasodilatory properties of NO have been exploited for over a century in cardiovascular disease, but NO donor drugs and inhaled NO are associated with significant shortcomings, including resistance to NO in some disease states, the development of tolerance during long-term treatment, and non-specific effects such as post-translational modification of proteins. The development of pharmacological agents capable of directly stimulating the NO receptor, soluble guanylate cyclase (sGC), is therefore highly desirable. The benzylindazole compound YC-1 was the first sGC stimulator to be identified; this compound formed a lead structure for the development of optimized sGC stimulators with improved potency and specificity for sGC, including CFM-1571, BAY 41-2272, BAY 41-8543, and BAY 63-2521. In contrast to the NO- and haem-independent sGC activators such as BAY 58-2667, these compounds stimulate sGC activity independent of NO and also act in synergy with NO to produce anti-aggregatory, anti-proliferative, and vasodilatory effects. Recently, aryl-acrylamide compounds were identified independent of YC-1 as sGC stimulators; although structurally dissimilar to YC-1, they have a similar mode of action and promote smooth muscle relaxation. Pharmacological stimulators of sGC may be beneficial in the treatment of a range of diseases, including systemic and pulmonary hypertension, heart failure, atherosclerosis, erectile dysfunction, and renal fibrosis. An sGC stimulator, BAY 63-2521, is currently in clinical development as an oral therapy for patients with pulmonary hypertension. It has demonstrated efficacy in a proof-of-concept study, reducing pulmonary vascular resistance and increasing cardiac output from baseline. A full, phase 2 trial of BAY 63-2521 in pulmonary hypertension is underway.

Inflammatory and thrombotic processes are associated with vascular dysfunction in children with familial hypercholesterolemia

BACKGROUND

Evidence suggests that children with familial hypercholesterolemia (FH) have endothelial dysfunction. Inflammatory and haemostatic abnormalities are associated with advanced atherosclerosis and increased cardiovascular events. However, it is unknown whether these abnormalities present in FH children and contribute to their vascular dysfunction.

METHODS AND RESULTS

We studied 38 children with FH (19 males, 19 females aged 14.8+/-0.9 years mean+/-S.E.) and 41 healthy children (controls; 22 males, 19 females aged 15.4+/-0.7 years). Endothelium-dependent reactive hyperemia (RH%) and endothelium-independent nitrate hyperemia dilatation (NH%) were measured by strain gauge plethysmography. Inflammatory and haemostatic parameters were assessed by ELISA. RH% and NH% were significantly reduced in FH compared to controls (91.3+/-9.3% vs. 120.4+/-10.6% and 53.6+/-3.8% vs. 74.5+/-7.4%, p<0.05 for both). Total cholesterol and lipoprotein (a) were increased in FH children compared to controls (282.3+/-8.8 mg/dl vs. 163.8+/-4.6 mg/dl and 11.0[4.6, 30.7]mg/dl vs. 5.24[2.63, 11.0]mg/dl median [IQR] respectively; p<0.001 for both). Intercellular cell adhesion molecule (ICAM-1) and interleukin 1 beta (IL-1 beta) serum levels were increased in FH compared to controls (p<0.05 and <0.001, respectively). Plasminogen activator inhibitor 1 (PAI-1) levels were also higher in FH children (p<0.001). Multivariate analysis revealed that reactive hyperemia was independently associated with nitrate-dependent reactive hyperemia (beta=0.597(0.199), p<0.01), PAI-1(beta=-6.78(2.65), p<0.05), log IL-1 beta (beta=-102.8 (30.2), p<0.01), age (beta=-5.06 (2.35), p<0.05) and FH status (beta=-25.2(10.6), p<0.05) (R(2) for the model: 0.63, p=0.001).

CONCLUSIONS

Inflammatory and haemostatic abnormalities are present in FH children and contribute to the endothelial dysfunction observed in these children.

Nitroglycerin-induced S-nitrosylation and desensitization of soluble guanylyl cyclase contribute to nitrate tolerance

Nitrates such as nitroglycerin (GTN) and nitric oxide donors such as S-nitrosothiols are clinically vasoactive through stimulation of soluble guanylyl cyclase (sGC), which produces the second messenger cGMP. Development of nitrate tolerance, after exposure to GTN for several hours, is a major drawback to a widely used cardiovascular therapy. We recently showed that exposure to nitric oxide and to S-nitrosothiols causes S-nitrosylation of sGC, which directly desensitizes sGC to stimulation by nitric oxide. We tested the hypothesis that desensitization of sGC by S-nitrosylation is a mechanism of nitrate tolerance. Our results established that vascular tolerance to nitrates can be recapitulated in vivo by S-nitrosylation through exposure to cell membrane-permeable S-nitrosothiols and that sGC is S-nitrosylated and desensitized in the tolerant, treated tissues. We next determined that (1) GTN treatment of primary aortic smooth muscle cells induces S-nitrosylation of sGC and its desensitization as a function of GTN concentration; (2) S-nitrosylation and desensitization are prevented by treatment with N-acetyl-cysteine, a precursor of glutathione, used clinically to prevent development of nitrate tolerance; and (3) S-nitrosylation and desensitization are reversed by cessation of GTN treatment. Finally, we demonstrated that in vivo development of nitrate tolerance and crosstolerance by 3-day chronic GTN treatment correlates with S-nitrosylation and desensitization of sGC in tolerant tissues. These results suggest that in vivo nitrate tolerance is mediated, in part, by desensitization of sGC through GTN-dependent S-nitrosylation.

Effect of oral organic nitrates on expression and activity of vascular soluble guanylyl cyclase

BACKGROUND AND PURPOSE

The regulation of vascular soluble guanylyl cyclase (sGC) expression by nitric oxide (NO) is still under discussion. In vitro, NO has been shown to downregulate the expression of sGC but it is unclear if this mechanism is operative in vivo and occurs during nitrate treatment.

EXPERIMENTAL APPROACH

We investigated whether high dose isosorbide mononitrate (ISMN) or pentaerythrityl tetranitrate (PETN) treatment changes vascular sGC expression and activity in vivo. New Zealand White rabbits received a standard diet, 2 or 200 mg ISMN kg(-1) d(-1) for 16 weeks, and C57BL/6 mice received a standard diet, 6, 60 or 300 mg PETN kg(-1) d(-1) for four weeks. Absorption was checked by measuring the plasma levels of the drug/metabolite.

KEY RESULTS

Western blots of rabbit aortic rings showed similar protein levels of sGC alpha1- (P=0.2790) and beta1-subunits (P=0.6900) in all groups. Likewise, ANOVA showed that there was no difference in the expression of sGC in lungs of PETN-treated mice (P=0.0961 for alpha1 and P=0.3709 for beta1). The activities of isolated sGC in response to SNAP (1 microM-1 mM) were identical in aortae of ISMN-treated rabbits (P=0.0775) and lungs of PETN-treated mice (P=0.6348). The aortic relaxation response to SNAP slightly decreased at high ISMN but not at high PETN.

CONCLUSIONS AND IMPLICATIONS

These data refute the hypothesis that therapeutic treatment with long acting NO donors has a significant impact on the regulation of vascular sGC expression and activity in vivo.

Prevention of nitroglycerin tolerance in vitro by T0156, a selective phosphodiesterase type 5 inhibitor

The efficacy of nitroglycerin as a vasodilator is limited by tolerance, which develops shortly after treatment begins. The present study aims to examine whether T0156, a newly developed potent and selective inhibitor of phosphodiesterase type 5 (PDE5), could attenuate the tolerance to nitroglycerin on rat aortas. Rat aortic rings were suspended in organ bath for the measurement of changes in isometric tension and nitrate tolerance was acutely induced by preceding exposure for 90 min to 30 microM nitroglycerin. Concentration-response curves to nitroglycerin were obtained on aortic rings pre-contracted with phenylephrine. Pre-exposure of rings with or without endothelium to nitroglycerin reduced the relaxations to nitroglycerin. The tissue levels of cyclic GMP were measured by enzyme immunoassay kit. Treatment with T0156 inhibited and prevented the reduced relaxation and cyclic GMP levels in response to nitroglycerin in tolerant rings. In contrast, nitroglycerin-induced tolerance was unaffected by cilostazol (PDE3 inhibitor) and rolipram (PDE4 inhibitor). Finally, incubation of aortic rings with thromboxane prostanoid receptor antagonist, cyclooxygenase inhibitor, or endothelin ET(A) receptor antagonist did not inhibit the development of tolerance. The present results suggest that nitroglycerin tolerance may involve an increased activity of PDE5 but not PDE3 or PDE4 isoforms in vascular smooth muscle cells since T0156 prevents the development of tolerance. Thromboxane A(2), cyclooxygenase (COX)-dependent prostaglandins and endothelin 1 play little role in the acute induction of nitroglycerin tolerance.

Hemodynamic effects of urotensin II and its specific receptor antagonist palosuran in cirrhotic rats

In cirrhosis, splanchnic vasodilation contributes to portal hypertension, subsequent renal sodium retention, and formation of ascites. Urotensin II(U-II) is a constrictor of large conductive vessels. Conversely, it relaxes mesenteric vessels, decreases glomerular filtration, and increases renal sodium retention. In patients with cirrhosis, U-II plasma levels are increased. Thus, we investigated hemodynamic and renal effects of U-II and its receptor antagonist, palosuran, in cirrhotic bile duct-ligated rats (BDL). In BDL and sham-operated rats, we studied acute effects of U-II (3 nmol/kg; intravenously) and palosuran (10 mg/kg; intravenously) and effects of oral administration of palosuran (30 mg/kg/day; 3 days) on hemodynamics and renal function. We localized U-II and U-II-receptor (UTR) in livers and portal veins by immunostaining. We determined U-II-plasma levels by enzyme-linked immunosorbent assay (ELISA), and mesenteric nitrite/nitrate-levels by Griess-reaction. RhoA/Rho-kinase and endothelial nitric oxide synthase (eNOS) pathways were determined by western blot analysis and reverse transcription polymerase chain reaction (RT-PCR) in mesenteric arteries. U-II plasma levels, as well as U-II and UTR-receptor expression in livers and portal veins of cirrhotic rats were significantly increased. U-II administration further augmented the increased portal pressure (PP) and decreased mean arterial pressure (MAP), whereas palosuran decreased PP without affecting MAP. The decrease in PP was associated with an increase in splanchnic vascular resistance. In mesenteric vessels, palosuran treatment up-regulated expression of RhoA and Rho-kinase, increased Rho-kinase-activity, and diminished nitric oxide (NO)/cyclic guanosine 3',5'-monophosphate (cGMP) signaling. Moreover, palosuran increased renal blood flow, sodium, and water excretion in BDL rats.

CONCLUSION

In BDL rats, U-II is a mediator of splanchnic vasodilation, portal hypertension and renal sodium retention. The U-II-receptor antagonist palosuran might represent a new therapeutic option in liver cirrhosis with portal hypertension.

Resistance to the nitric oxide/cyclic guanosine 5'-monophosphate/protein kinase G pathway in vascular smooth muscle cells from the obese Zucker rat, a classical animal model of insulin resistance: role of oxidative stress

Some in vivo and ex vivo studies demonstrated a resistance to the vasodilating effects of nitric oxide (NO) in insulin-resistant states and, in particular, obese Zucker rats (OZR). To evaluate the biochemical basis of this phenomenon, we aimed to identify defects of the NO/cGMP/cGMP-dependent protein kinase (PKG) pathway in cultured vascular smooth muscle cells (VSMCs) from OZR and lean Zucker rats (LZR) by measuring: 1) NO donor ability to increase cGMP in the absence and presence of inhibitors of soluble guanylate cyclase (sGC) and phosphodiesterases (PDEs); 2) NO and cGMP ability to induce, via PKG, vasodilator-stimulated phosphoprotein (VASP) phosphorylation at serine 239 and PDE5 activity; 3) protein expression of sGC, PKG, total VASP, and PDE5; 4) superoxide anion concentrations and ability of antioxidants (superoxide dismutase+catalase and amifostine) to influence the NO/cGMP/PKG pathway activation; and 5) hydrogen peroxide influence on PDE5 activity and VASP phosphorylation. VSMCs from OZR vs. LZR showed: 1) baseline cGMP concentrations higher, at least in part owing to reduced catabolism by PDEs; 2) impairment of NO donor ability to increase cGMP, even in the presence of PDE inhibitors, suggesting a defect in the NO-induced sGC activation; 3) reduction of NO and cGMP ability to activate PKG, indicated by the impaired ability to phosphorylate VASP at serine 239 and to increase PDE5 activity via PKG; 4) similar baseline protein expression of sGC, PKG, total VASP, and PDE5; and 5) higher levels of superoxide anion. Antioxidants partially prevented the defects of the NO/cGMP/PKG pathway observed in VSMCs from OZR, which were reproduced by hydrogen peroxide in VSMCs from LZR, suggesting the pivotal role of oxidative stress.

Reversal of tolerance to nitroglycerin with vinpocetine: A role of calcitonin gene-related peptide

Previous studies have shown that the development of tolerance to nitroglycerin is related to reduction of endogenous calcitonin gene-related peptide (CGRP) release. In the present study, Nitroglycerin caused a concentration-dependent relaxation concomitantly with a significant increase in the release of CGRP in the isolated rat thoracic aorta, an effect that was reduced by preincubation with capsaicin. Pretreatment with nitroglycerin significantly decreased its vasodilation and depressor effect and the release of CGRP, which was restored in the presence of vinpocetine, an inhibitor of phosphodiesterase. The present results suggest that reversal of tolerance to nitroglycerin with vinpocetine is related to the increased release of CGRP in the rat.

Role of cGMP-dependent protein kinase in development of tolerance to nitroglycerine in porcine coronary arteries

BACKGROUND AND PURPOSE

The cGMP-dependent protein kinase (PKG) is a key enzyme for nitrovasodilator-induced vasodilation. The present study was to determine its role in nitrate tolerance.

EXPERIMENTAL APPROACH

isolated porcine coronary arteries were incubated for 24 h with nitroglycerin (NTG) and their relaxant responses were determined. PKG activity was assayed by measuring the incorporation of (32)P into BPDEtide. PKG protein was determined by Western blotting and PKG mRNA by real-time PCR.

KEY RESULTS

A 24 h incubation with NTG attenuated relaxation of coronary arteries to NTG, which was associated with decreased PKG activity. The nitrate tolerance induced with NTG at 10(-7) M was affected by a scavenger of reactive oxygen species and the tolerance induced with NTG at 10(-6) and 10(-5) M showed cross-tolerance to DETA NONOate and 8-Br-cGMP (a cell permeable cGMP analogue). PKG protein and mRNA were down-regulated by a 24 h incubation with NTG at 10(-5) M but not at 10(-7) M. Acute exposure to exogenous superoxide inhibited PKG activity stimulated by NTG at 10(-7) M but not at 10(-5) M. Superoxide had no effect on PKG activity stimulated with exogenous cGMP.

CONCLUSIONS AND IMPLICATIONS

Nitrate tolerance induced by NTG at low concentrations may result from an increased production of reactive oxygen species acting on sites upstream of PKG. The tolerance induced by NTG at higher concentrations may be in part due to suppression of PKG expression resulting from sustained activation of the enzyme. These distinct mechanisms of nitrate tolerance may be of clinical significance.

Oxidative inhibition of the mitochondrial aldehyde dehydrogenase promotes nitroglycerin tolerance in human blood vessels

OBJECTIVES

We tested the hypothesis of whether an inhibition of the nitroglycerin (GTN) bioactivating enzyme mitochondrial aldehyde dehydrogenase (ALDH-2) contributes to GTN tolerance in human blood vessels.

BACKGROUND

The hemodynamic effects of GTN are rapidly blunted by the development of tolerance, a phenomenon associated with increased formation of reactive oxygen species (ROS). Recent studies suggest that ROS-induced inhibition of ALDH-2 accounts for tolerance in animal models.

METHODS

Segments of surgically removed arteria mammaria and vena saphena from patients undergoing coronary bypass surgery were used to examine the vascular responsiveness to GTN and the endothelium-dependent vasodilator acetylcholine. The ALDH-2 activity and expression in these segments were assessed by the conversion of a benzaldehyde or its derivative to the benzoic acid metabolite and by Western blotting technique.

RESULTS

In contrast to patients not treated with nitrates (n = 36), patients treated with GTN for 48 h (n = 14) before surgery showed tolerance to GTN and endothelial dysfunction in arterial and venous vessels. In vivo GTN tolerance was mimicked in vitro by incubation of nontolerant vessels with the ALDH-2 inhibitor benomyl. In vivo GTN treatment decreased vascular aldehyde dehydrogenase activity compared with nontolerant vessels and decreased the expression of ALDH-2 in arterial tissue. Incubation of control venous vessels with GTN caused a significant attenuation of aldehyde dehydrogenase activity that was reversed by presence of the sulfhydryl group donor dithiothreitol.

CONCLUSIONS

Long-term GTN treatment induces tolerance and endothelial dysfunction in human vessels, associated with an inhibition and down-regulation of vascular ALDH-2. Thus, these findings extend results of previous animal studies to humans.

Comparative study of nicorandil and a spasmolytic cocktail in preventing radial artery spasm during transradial coronary angiography

BACKGROUND

Radial artery spasm is one of the most common complications during coronary angiography via the transradial approach, causing patient discomfort or sometimes interrupting the procedure. This study was designed to compare the spasmolytic effect between nicorandil and a cocktail during transradial coronary angiography.

METHODS

A randomized study to compare 4 mg of nicorandil and a cocktail (mixture of normal saline, 200 microg of verapamil) was performed in 150 patients. We examined vasospasms of the radial artery that were expressed as stenosis of the radial artery vessel diameter after the procedure.

RESULT

The reductions of systolic and diastolic blood pressures showed no significant differences between the two groups (15.4+/-11.5/7.7+/-7.8 mmHg for nicorandil and 16.3+/-13.4/6.2 mmHg for cocktail). Both agents induced a significant radial artery vasodilation after transradial administration at proximal and mid segments (P < 0.001 for all). Nicorandil showed a significant increase of the mean change of the radial artery diameter compared to the cocktail at mid-segment (0.32+/-0.23 mm for nicorandil and 0.24+/-0.15 mm for a cocktail, P < 0.05). There was no statistically significant difference between the two groups in radial artery spasm (50.7% vs. 52.0% in nicorandil and a cocktail, respectively) after catheterization.

CONCLUSION

Nicorandil with vasodilator effects by a dual mechanism was effective as the cocktail in preventing radial artery spasm during transradial coronary angiography.

Chronic nitrates blunt the effects of not only nitric oxide but also natriuretic peptides in cardiac myocytes

Exposure to nitrates causes tachyphylaxis to nitric oxide (NO), which reduces the effects of the second messenger cyclic guanosine-3',-5'-monophosphate (cyclic GMP). We tested the hypothesis that prolonged exposure to NO would also blunt the effects of natriuretic peptides. Cardiac myocytes were isolated from control (N=7) and chronic nitroglycerin (patched, N=7) rabbits. Patched animals received a transdermal nitroglycerin patch (0.3mg/h for 5 days). Myocyte function was determined at baseline, after C-type natriuretic peptide (CNP, 10(-8) and 10(-7)M) or brain natriuretic peptide (BNP, 10(-8) and 10(-7)M) or S-nitroso-N-acetyl-penicilliamine (SNAP, a NO donor, 10(-6) and 10(-5)M) followed by KT5823 (a cyclic GMP protein kinase inhibitor, 10(-6)M). Soluble and particulate guanylyl cyclase activities were measured in vitro and phosphoprotein analysis was performed. In control animals, CNP 10(-8)M (5.14+/-0.5%) and 10(-7)M (4.4+/-0.7%) significantly reduced percentage shortening from baseline (6.1+/-1.6%). KT5823 restored percentage shortening to 4.9+/-0.8%. Similar data were obtained with BNP and SNAP. In patched animals, CNP, BNP, SNAP had no significant effects on percentage shortening. The data on maximal rate of shortening and relaxation were consistent with these results. Guanylyl cyclase activities were not different in the control and patched animals. The myocytes from control and patched animals had similar protein phosphorylation patterns. Our data suggested that in addition to NO, the responses to both natriuretic peptides were downregulated after chronic exposure to nitroglycerin, but these effects were not due to changes in either guanylyl cyclase or cyclic GMP protein kinase, suggesting an altered downstream pathway.