Involvement of the endothelial DDAH/ADMA pathway in nitroglycerin tolerance: the role of ALDH-2

S-Nitrosylation of Prostacyclin Synthase Instigates Nitrate Cross-Tolerance In Vivo

Development of nitrate tolerance is a major drawback to nitrate therapy. Prostacyclin (PGI2) is a powerful vasodilator produced from prostaglandin (PGH2) by prostacyclin synthase (PGIS) in endothelial cells. This study aimed to determine the role of PGIS S-nitrosylation in nitrate tolerance induced by nitroglycerin (GTN). In endothelial cells, GTN increased PGIS S-nitrosylation and disturbed PGH2 metabolism, which were normalized by mutants of PGIS cysteine 231/441 to alanine (C231/441A). Clearance of nitric oxide by carboxy-PTIO or inhibition of S-nitrosylation by N-acetyl-cysteine decreased GTN-induced PGIS S-nitrosylation. Enforced expression of mutated PGIS with C231/441A markedly abolished GTN-induced PGIS S-nitrosylation and nitrate cross-tolerance in Apoe^-/- mice. Inhibition of cyclooxygenase 1 by aspirin, supplementation of PGI2 by beraprost, and inhibition of PGIS S-nitrosylation by N-acetyl-cysteine improved GTN-induced nitrate cross-tolerance in rats. In patients, increased PGIS S-nitrosylation was associated with nitrate tolerance. In conclusion, GTN induces nitrate cross-tolerance through PGIS S-nitrosylation at cysteine 231/441.

Induction of microRNA-199 by Nitric Oxide in Endothelial Cells Is Required for Nitrovasodilator Resistance via Targeting of Prostaglandin I2 Synthase

Background:

Nitrates are widely used to treat coronary artery disease, but their therapeutic value is compromised by nitrate tolerance, because of the dysfunction of prostaglandin I2 synthase (PTGIS). MicroRNAs repress target gene expression and are recognized as important epigenetic regulators of endothelial function. The aim of this study was to determine whether nitrates induce nitrovasodilator resistance via microRNA-dependent repression of PTGIS gene expression.

Methods:

Nitrovasodilator resistance was induced by nitroglycerin (100 mg·kg –1 ·d –1 , 3 days) infusion in Apoe –/– mice. The responses of aortic arteries to nitric oxide donors were assessed in an organ chamber. The expression levels of microRNA-199 (miR-199)a/b were assayed by quantitative reverse transcription polymerase chain reaction or fluorescent in situ hybridization.

Results:

In cultured human umbilical vein endothelial cells, nitric oxide donors induced miR-199a/b endogenous expression and downregulated PTGIS gene expression, both of which were reversed by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt or silence of serum response factor. Evidence from computational and luciferase reporter gene analyses indicates that the seed sequence of 976 to 982 in the 3′-untranslated region of PTGIS mRNA is a target of miR-199a/b. Gain functions of miR-199a/b resulting from chemical mimics or adenovirus-mediated overexpression increased PTGIS mRNA degradation in HEK293 cells and human umbilical vein endothelial cells. Furthermore, nitroglycerin-decreased PTGIS gene expression was prevented by miR-199a/b antagomirs or was mirrored by the enforced expression of miR-199a/b in human umbilical vein endothelial cells. In Apoe –/– mice, nitroglycerin induced the ectopic expression of miR-199a/b in the carotid arterial endothelium, decreased PTGIS gene expression, and instigated nitrovasodilator resistance, all of which were abrogated by miR-199a/b antagomirs or LNA—anti–miR-199. It is important that the effects of miR-199a/b inhibitions were abolished by adenovirus-mediated PTGIS deficiency. Moreover, the enforced expression of miR-199a/b in vivo repressed PTGIS gene expression and impaired the responses of aortic arteries to nitroglycerin/sodium nitroprusside/acetylcholine/cinaciguat/riociguat, whereas the exogenous expression of the PTGIS gene prevented nitrovasodilator resistance in Apoe –/– mice subjected to nitroglycerin infusion or miR-199a/b overexpression. Finally, indomethacin, iloprost, and SQ29548 improved vasorelaxation in nitroglycerin-infused Apoe –/– mice, whereas U51605 induced nitrovasodilator resistance. In humans, the increased expressions of miR-199a/b were closely associated with nitrate tolerance.

Conclusions:

Nitric oxide–induced ectopic expression of miR-199a/b in endothelial cells is required for nitrovasodilator resistance via the repression of PTGIS gene expression. Clinically, miR-199a/b is a novel target for the treatment of nitrate tolerance.

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.

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.

Nitroglycerine-induced nitrate tolerance compromises propofol protection of the endothelial cells against TNF-α: the role of PKC-β2 and NADPH oxidase

Continuous treatment with organic nitrates causes nitrate tolerance and endothelial dysfunction, which is involved with protein kinase C (PKC) signal pathway and NADPH oxidase activation. We determined whether chronic administration with nitroglycerine compromises the protective effects of propofol against tumor necrosis factor (TNF-) induced toxicity in endothelial cells by PKC-β₂ dependent NADPH oxidase activation. Primary cultured human umbilical vein endothelial cells were either treated or untreated with TNF-α (40 ng/mL) alone or in the presence of the specific PKC-β₂ inhibitor CGP53353 (1 μM)), nitroglycerine (10 μM), propofol (100 μM), propofol plus nitroglycerin, or CGP53353 plus nitroglycerine, respectively, for 24 hours. TNF-α increased the levels of superoxide, Nox (nitrate and nitrite), malondialdehyde, and nitrotyrosine production, accompanied by increased protein expression of p-PKC-β₂, gP91phox, and endothelial cell apoptosis, whereas all these changes were further enhanced by nitroglycerine. CGP53353 and propofol, respectively, reduced TNF-α induced oxidative stress and cell toxicity. CGP53353 completely prevented TNF-α induced oxidative stress and cell toxicity in the presence or absence of nitroglycerine, while the protective effects of propofol were neutralized by nitroglycerine. It is concluded that nitroglycerine comprises the protective effects of propofol against TNF-α stimulation in endothelial cells, primarily through PKC-β₂ dependent NADPH oxidase activation.

Nutraceutical strategies for ameliorating the toxic effects of alcohol

Rodent studies reveal that oxidative stress, much of it generated via induction/activation of NADPH oxidase, is a key mediator of a number of the pathogenic effects of chronic ethanol overconsumption. The highly reactive ethanol metabolite acetaldehyde is a key driver of this oxidative stress, and doubtless works in other ways to promote alcohol-induced pathology. Effective antioxidant measure may therefore be useful for mitigating the adverse health consequences of alcohol consumption; spirulina may have particular utility in this regard, as its chief phycochemical phycocyanobilin has recently been shown to function as an inhibitor of certain NADPH oxidase complexes, mimicking the physiological role of its chemical relatives biliverdin/bilirubin in this respect. Moreover, certain nutraceuticals, including taurine, pantethine, and lipoic acid, may have the potential to boost the activity of the mitochondrial isoform of aldehyde dehydrogenase, ALDH-2, accelerating conversion of acetaldehyde to acetate (which arguably has protective health effects). Little noticed clinical studies conducted nearly three decades ago reported that pre-ingestion of either taurine or pantethine could blunt the rise in blood acetaldehyde following ethanol consumption. Other evidence suggests that lipoic acid may function within mitochondria to maintain aldehyde dehydrogenase in a reduced active conformation; the impact of this agent on ethanol metabolism has however received little or no study. Studies evaluating the impact of nutracetical strategies on prevention of hangovers - which likely are mediated by acetaldehyde - may represent a quick, low-cost way to identify nutraceutical regimens that merit further attention for their potential impact on alcohol-induced pathology. Measures which boost or preserve ALDH-2 activity may also have important antioxidant potential, as this enzyme functions physiologically to protect cells from toxic aldehydes generated by oxidant stress.

Preserving mitochondrial function prevents the proteasomal degradation of GTP cyclohydrolase I

The development of pulmonary hypertension is a common accompaniment of congenital heart disease (CHD) with increased pulmonary blood flow. Our recent evidence suggests that asymmetric dimethylarginine (ADMA)-induced mitochondrial dysfunction causes endothelial nitric oxide synthase (eNOS) uncoupling secondary to a proteasome-dependent degradation of GTP cyclohydrolase I (GCH1) that results in a decrease in the NOS cofactor tetrahydrobiopterin (BH(4)). Decreases in NO signaling are thought to be an early hallmark of endothelial dysfunction. As l-carnitine plays an important role in maintaining mitochondrial function, in this study we examined the protective mechanisms and the therapeutic potential of l-carnitine on NO signaling in pulmonary arterial endothelial cells and in a lamb model of CHD and increased pulmonary blood flow (Shunt). Acetyl-l-carnitine attenuated the ADMA-mediated proteasomal degradation of GCH1. This preservation was associated with a decrease in the association of GCH1 with Hsp70 and the C-terminus of Hsp70-interacting protein (CHIP) and a decrease in its ubiquitination. This in turn prevented the decrease in BH(4) levels induced by ADMA and preserved NO signaling. Treatment of Shunt lambs with l-carnitine also reduced GCH1/CHIP interactions, attenuated the ubiquitination and degradation of GCH1, and increased BH(4) levels compared to vehicle-treated Shunt lambs. The increases in BH(4) were associated with decreased NOS uncoupling and enhanced NO generation. Thus, we conclude that L-carnitine may have a therapeutic potential in the treatment of pulmonary hypertension in children with CHD with increased pulmonary blood flow.

Decreased anandamide transporter activity and calcitonin gene-related peptide production in spontaneously hypertensive rats: role of angiotensin II

In the present study, we investigated the role of angiotensin II in regulating the anandamide transporter activity and resultant calcitonin gene-related peptide (CGRP) production in spontaneously hypertensive rats (SHRs). Systolic blood pressure, plasma levels of anandamide, angiotensin II and CGRP, CGRP mRNA expression in dorsal root ganglion and anandamide transporter activity in peripheral blood lymphocytes were measured in SHRs treated with selective angiotensin II type 1 receptor antagonist losartan. Rat peripheral blood lymphocytes were isolated to examine the effect of exogenous angiotensin II on anandamide-induced CGRP mRNA expression, anandamide transporter activity and intracellular reactive oxygen species production in presence or absence of losartan and antioxidant n-acetyl-cysteine. In SHRs, the plasma level of angiotensin II and anandamide was elevated, but the anandamide transporter activity was attenuated concomitantly with decreased CGRP production. Treatment with losartan for 2weeks produced depressor effect, restored the reduced anandamide transporter activity, decreased the plasma anandamide level and increased the plasma level and mRNA expression of CGRP in SHRs. In cultured lymphocytes, up-regulation of CGRP mRNA expression by exogenous administration of anandamide was inhibited by anandamide transporter blocker and angiotensin II. Angiotensin II also inhibited the anandamide transporter activity concentration-dependently while increased intracellular reactive oxygen species production, which was reversed by pretreatment with losartan or n-acetyl-cysteine. The present findings suggest that angiotensin II plays a critical role in mediating the decrease in anandamide transporter activity and CGRP production in SHRs, which is likely due to activation angiotensin II type 1 receptor and resultant reactive oxygen species production.

Comparative proteomic analysis of cellular response of human airway epithelial cells (A549) to benzo(a)pyrene

This work aimed to investigate the cellular response of human airway epithelial cells (A549) to oxidative stress induced by benzo(a)pyrene [B(a)P]. Levels of intracellular reactive oxygen species (ROS) and lipid peroxidation were investigated in A549 cells treated with varying concentrations of B(a)P. A comparative proteomic analysis of total proteins was performed in cells treated with 1 µM B(a)P [B(a)P-1] and untreated cells. The expression of Mn superoxide dismutase (Mn SOD), one of the identified down-regulated proteins in B(a)P-1 cells, was then analyzed by Western blotting. The total antioxidant activity, total superoxide dismutase activity, catalase (CAT) activity, and glutathione reductase (GR) activity were all analyzed after B(a)P treatment. Our results demonstrated that 1 µM B(a)P could induce ROS generation and lead to lipid peroxidation in A549 cells, and 23 differentially expressed proteins were identified. The expression levels of Mn SOD and the total SOD were induced at 0.1 µM and suppressed at 1 µM and 10 µM. Up-regulation of CAT and GR activity resulted in an increase in total antioxidant activity in A549 after exposure to B(a)P. These findings provide a basis for understanding the mechanisms of mitochondrial dysfunction and perturbation of antioxidant status induced by B(a)P on airway epithelial cells.

Continuous therapy with transdermal nitroglycerin does not affect biomarkers of vascular inflammation and injury in healthy volunteers

Continuous exposure to nitroglycerin (GTN) results in development of tolerance and is associated with increased free radical production and abnormal endothelial function. Elevated plasma biomarkers of inflammation have been shown to be associated with endothelial dysfunction in most cardiovascular conditions. It remains unclear whether exposure to GTN is also associated with increased biomarkers of endothelial and vascular injury or vascular inflammation. In an investigator-blind study, a total of 28 healthy volunteers were randomized to continuous therapy with GTN (0.6 mg/h 24 h/day for 7 days) or no therapy. Venous blood was collected on day 0 and day 7. Plasma levels of markers such as asymmetric dimethyl-arginine (ADMA), human soluble P-selectin, interleukin-6, tumor necrosis factor-alpha, intercellular adhesion molecule-1, and oxidized low-density lipoproteins were measured. The levels of blood markers on day 0 were similar in the control and GTN-treated groups. After 7 days of GTN exposure, there were no significant changes in the different markers of vascular inflammation and injury either in the GTN or control group (all p > 0.5). The present study documents that prolonged continuous therapy with transdermal GTN therapy is not associated with changes in markers of vascular inflammation and injury.

Protective effects of kaempferol against endothelial damage by an improvement in nitric oxide production and a decrease in asymmetric dimethylarginine level

Previous investigations have shown that asymmetric dimethylarginine (ADMA) inhibits nitric oxide (NO) synthases (NOS) and that ADMA is a risk factor for endothelial dysfunction. The objective of this study was to investigate the protective effect of kaempferol, a naturally occurring flavonoid antioxidant agent, against endothelial damage and the mechanisms involved. The experiments were performed in aorta and plasma from C57BL/6J control and apolipoprotein E-deficient (ApoE(-/-)) mice treated or not with kaempferol (50 or 100mg/kg, intragastrically) for 4 weeks, and in human umbilical vein endothelial cells (HUVECs) pretreated or not with kaempferol (1, 3 or 10 microM) for 1h and exposed to lysophosphatidylcholine (LPC) (10 microg/mL) for 24h. Kaempferol treatment improved endothelium-dependent vasorelaxation, increased the maximal relaxation value, and decreased the half-maximum effective concentration concomitantly with an increase in nitric oxide plasma concentration, a decrease in ADMA and malondialdehyde (MDA) plasma concentrations, and increase in the expression of aortic endothelial NOS (eNOS) as well as dimethylarginine dimethylaminohydrolase II (DDAH II) in ApoE(-/-) mice. In addition, LPC caused a reduction in NO production, an increase in ADMA concentration concomitantly with a decreased expression of eNOS and DDAH II in HUVECs, and the effect of LPC was abolished by kaempferol. Treatment with kaempferol also significantly decreased reactive oxygen species production in mice aorta and in HUVECs. The present results suggest that the protective effect of kaempferol against endothelial damage may be associated with an improvement in NO production and a decrease in ADMA level.

Dimethylarginine dimethylaminohydrolase regulation: a novel therapeutic target in cardiovascular disease

Asymmetric dimethylarginine (ADMA), an endogenous methylated form of the amino acid L-arginine, inhibits the activity of the enzyme endothelial nitric oxide synthase, with consequent reduced synthesis of nitric oxide. ADMA is metabolised to L-citrulline and dimethylamine by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). The modulation of DDAH activity and expression plays a pivotal role in regulating intracellular ADMA concentrations, with important effects on vascular homeostasis. For example, impairment in DDAH activity, resulting in elevated ADMA concentrations and reduced nitric oxide synthesis, can promote the onset and progression of atherosclerosis in experimental models. This review discusses the current role of ADMA and DDAH in vascular health and disease, the techniques used to assess DDAH activity and expression, and the results of recent studies on pharmacological and biological agents modulating DDAH activity and expression. Suggestions for future basic and clinical research directions are also discussed.