After 130 years, the molecular mechanism of action of nitroglycerin is revealed

Effects of beetroot juice on blood pressure in hypertension according to European Society of Hypertension Guidelines: A systematic review and meta-analysis

AIMS

It has been suggested that nitrate-rich beetroot juice (BRJ) reduces blood pressure (BP) in various populations. We aimed to investigate the effect of BRJ on BP in adults with hypertension according to the European Society of Hypertension Guidelines (clinical BP ≥ 140/≥ 90 mmHg) and whether BRJ can be considered as an adjunct to hypertension drug treatment, by conducting a meta-analysis of randomized controlled trials.

DATA SYNTHESIS

PubMed, SCOPUS, Medline Ovid, Cinahl, Cochrane Library and Web of Science were searched from inception until April 13, 2024 to identify randomized controlled trials of BRJ versus placebo, water, or no intake. Risk of bias was assessed using a standardized appraisal instrument from the Swedish Agency for Health Technology and Assessment of Social Services, which is based on the Cochrane risk-of-bias tool for randomized trials. The pooled BP effect size was calculated using random effects models and meta-regression. Certainty of evidence was assessed using GRADE. Eleven trials (349 patients) were included. BRJ yielded a significant reduction in clinical systolic BP compared with placebo mean difference (MD) -5.31 mmHg (95% CI -7.46, -3.16; I2 = 64%, GRADE ⊕⊕OO). There was no significant effect on clinical diastolic BP or 24-h BP outcomes, and the heterogeneity was moderate to high.

CONCLUSIONS

Daily ingestion of 200-800 mg of nitrate from BRJ may reduce clinical systolic BP in hypertensive individuals with no sign of development of tolerance. Certainty of evidence is low, and results should be interpreted with caution.

Nitroglycerin: a comprehensive review in cancer therapy

Nitroglycerin (NTG) is a prodrug that has long been used in clinical practice for the treatment of angina pectoris. The biotransformation of NTG and subsequent release of nitric oxide (NO) is responsible for its vasodilatating property. Because of the remarkable ambivalence of NO in cancer disease, either protumorigenic or antitumorigenic (partly dependent on low or high concentrations), harnessing the therapeutic potential of NTG has gain interest to improve standard therapies in oncology. Cancer therapeutic resistance remains the greatest challenge to overcome in order to improve the management of cancer patients. As a NO releasing agent, NTG has been the subject of several preclinical and clinical studies used in combinatorial anticancer therapy. Here, we provide an overview of the use of NTG in cancer therapy in order to foresee new potential therapeutic avenues.

Assessing emerging technologies from an arms control perspective

Developments in science and technology improve health and wellbeing of humankind, for example with better methods to detect and treat diseases. However, some advances have led to the development of weapons of mass destruction: chemical and biological weapons. Although banned by international treaties, chemical weapons have been used in recent years in assassinations and the Syrian civil war. Additionally, biological weapons became the subject of recent suspicions and allegations. While not limited to these fields, the so-called dual-use potential-the possibility to apply aspects both with benevolent or malevolent intentions-is especially pronounced in the life sciences. Here, we showcase some areas explored at the conference series Spiez CONVERGENCE that facilitates an exchange between science, arms control and international security. Together, these communities discuss the potential impact of life scientific advances on the Chemical and Biological Weapons Conventions. Enabled by digital technologies, DNA sequencing and synthesis provide the toolbox to (re)construct viruses and cells, which demonstrated invaluable during the COVID-19 pandemic but bear the misuse risk to allow intentionally triggering an outbreak. Open databases and algorithms could be used to generate new chemical weapons. We argue that preventing unintended consequences of life science research while promoting its benefits with responsible science, requires awareness and reflection about unexpected risks of everyone involved in the research process. The strength of the ban of chemical and biological weapons also depends on scientists interacting with policy makers in evaluating risks and implementing measures to reduce them.

Nitrate Water Contamination from Industrial Activities and Complete Denitrification as a Remediation Option

Freshwater is a scarce resource that continues to be at high risk of pollution from anthropogenic activities, requiring remediation in such cases for its continuous use. The agricultural and mining industries extensively use water and nitrogen (N)-dependent products, mainly in fertilizers and explosives, respectively, with their excess accumulating in different water bodies. Although removal of NO3 from water and soil through the application of chemical, physical, and biological methods has been studied globally, these methods seldom yield N2 gas as a desired byproduct for nitrogen cycling. These methods predominantly cause secondary contamination with deposits of chemical waste such as slurry brine, nitrite (NO2), ammonia (NH3), and nitrous oxide (N2O), which are also harmful and fastidious to remove. This review focuses on complete denitrification facilitated by bacteria as a remedial option aimed at producing nitrogen gas as a terminal byproduct. Synergistic interaction of different nitrogen metabolisms from different bacteria is highlighted, with detailed attention to the optimization of their enzymatic activities. A biotechnological approach to mitigating industrial NO3 contamination using indigenous bacteria from wastewater is proposed, holding the prospect of optimizing to the point of complete denitrification. The approach was reviewed and found to be durable, sustainable, cost effective, and environmentally friendly, as opposed to current chemical and physical water remediation technologies.

Glyceryl Trinitrate: History, Mystery, and Alcohol Intolerance

Glyceryl trinitrate (GTN) is one of the earliest known treatments for angina with a fascinating history that bridges three centuries. However, despite its central role in the nitric oxide (NO) story as a NO-donating compound, establishing the precise mechanism of how GTN exerts its medicinal benefit has proven to be far more difficult. This review brings together the explosive and vasodilatory nature of this three-carbon molecule while providing an update on the likely in vivo pathways through which GTN, and the rest of the organic nitrate family, release NO, nitrite, or a combination of both, while also trying to explain nitrate tolerance. Over the last 20 years the alcohol detoxification enzyme, aldehyde dehydrogenase (ALDH), has undoubtedly emerged as the front runner to explaining GTN's bioactivation. This is best illustrated by reduced GTN efficacy in subjects carrying the single point mutation (Glu504Lys) in ALDH, which is also responsible for alcohol intolerance, as characterized by flushing. While these findings are significant for anyone following the GTN story, they appear particularly relevant for healthcare professionals, and especially so, if administering GTN to patients as an emergency treatment. In short, although the GTN puzzle has not been fully solved, clinical study data continue to cement the importance of ALDH, as uncovered in 2002, as a key GTN activator.

Carbon Monoxide and Nitric Oxide as Examples of the Youngest Class of Transmitters

The year 2021 is the 100th anniversary of the confirmation of the neurotransmission phenomenon by Otto Loewi. Over the course of the hundred years, about 100 neurotransmitters belonging to many chemical groups have been discovered. In order to celebrate the 100th anniversary of the confirmation of neurotransmitters, we present an overview of the first two endogenous gaseous transmitters i.e., nitric oxide, and carbon monoxide, which are often termed as gasotransmitters.

Biotransformation of organic nitrates by glutathione S-transferases and other enzymes: An appraisal of the pioneering work by William B. Jakoby

Organic nitrates (R-ONO₂; R, organic residue) such as nitroglycerin are used as drugs in part for more than a century. Their pharmacological use is associated with clinically relevant tolerance which is reportedly known since 1888. The underlying mechanisms of both, the mechanisms of action and the main pharmacological effect, which is vasodilatation and reduction of blood pressure, and the development of tolerance, which means increasing need of drug amount in sustained long-term therapy, are still incompletely understood. William B. Jakoby and associates were the first to report the biotransformation of organic nitrates, notably including nitroglycerin (i.e., glycerol trinitrate; GTN), by glutathione S-transferase (GST)-catalyzed conjugation of glutathione (GSH) to the nitrogen atom of one of the three nitrate groups of GTN to generate glutathione sulfenyl nitrite (glutathione thionitrate, S-nitroglutathione; GSNO₂). Jakoby's group was also the first to suggest that GSNO₂ reacts with a second GSH molecule to produce inorganic nitrite (ONO^-) and glutathione disulfide (GSSG) without the catalytic involvement of GST. This mechanism has been adopted by others to the biotransformation of GTN by mitochondrial aldehyde dehydrogenase (mtALDH-(CysSH)₂) which does not require GSH as a substrate. The main difference between these reactions is that mtALDH forms an internal thionitrate (mtALDH-(CysSH)-CysSNO₂) which releases inorganic nitrite upon intra-molecular reaction to form mtALDH disulfide (mtALDH-(CysS)₂). Subsequently, ONO^- and GSNO₂ are reduced by several proteins and enzymes to nitric oxide (NO) which is a very potent activator of soluble guanylyl cyclase to finally relax the smooth muscles thus dilating the vasculature. GSNO₂ is considered to rearrange to GSONO which undergoes further reactions including GSNO and GSSG formation. The present article is an appraisal of the pioneering work of William B. Jakoby in the area of the biotransformation of organic nitrates by GST. The two above mentioned enzymatic reactions are discussed in the context of tolerance development to organic nitrates, still a clinically relevant pharmacological concern.

Pharmacologic Control of Blood Pressure in Infants and Children

Alterations in blood pressure are common during the perioperative period in infants and children. Perioperative hypertension may be the result of renal failure, volume overload, or activation of the sympathetic nervous system. Concerns regarding end-organ effects or postoperative bleeding may mandate regulation of blood pressure. During the perioperative period, various pharmacologic agents have been used for blood pressure control including sodium nitroprusside, nitroglycerin, β-adrenergic antagonists, fenoldopam, and calcium channel antagonists. The following manuscript outlines the commonly used pharmacologic agents for perioperative BP including dosing regimens and adverse effect profiles. Previously published clinical trials are discussed and efficacy in the perioperative period reviewed.

Co-treatment with nitroglycerin and metformin exhibits physicochemically and pathohistologically detectable anticancer effects on fibrosarcoma in hamsters

We investigated the effect of nitroglycerin with metformin on fibrosarcoma in hamsters. Syrian golden hamsters of both sexes, weighing approximately 60 g, were randomly allocated to control and experimental groups, with 8 animals per group. In all groups, 2 × 10⁶ BHK-21/C13 cells in 1 ml were injected subcutaneously into the animals' backs. Peroral treatment carried out with nitroglycerin 25 mg/kg daily, or with metformin 500 mg/kg daily, or with a combination of nitroglycerin 25 mg/kg and metformin 500 mg/kg daily. Later validation experiments were conducted with double doses of the single therapy and additional rescue doses of mebendazole 460 mg/kg daily, via a gastric probe after tumor inoculation. After 2 weeks, when the tumors were approximately 2-3 cm in the control group, all animals were sacrificed. Blood samples were collected for hematological and biochemical analyses, the tumors were excised and weighed, and their diameters and volumes were measured. The tumor samples were pathohistologically and immunohistochemically assessed for proliferation marker protein Ki-67, proliferating cell nuclear antigen PCNA, hematopoietic progenitor cell antigen CD34, cluster of differentiation 31 (CD31), cytochrome c oxidase subunit 4 (COX4), mitochondria marker Cytochrome C, glucose transporter 1 (GLUT1) and inducible nitric oxide synthase (iNOS), and the main organs were toxicologically tested. The Ki-67 and PCNA positivity and the cytoplasmic marker (CD34, CD31, COX4, Cytochrome C, GLUT1, iNOS) immunoexpression in the tumor samples were quantified. The combination of nitroglycerin and metformin significantly inhibited fibrosarcoma growth in hamsters without toxicity, compared to monotherapy or control. The results were validated and confirmed in the subsequently accomplished experiment with doubled doses of the single drug therapy and in the rescue experiment with addition of mebendazole. The single treatments did not show significant antisarcoma effect, regardless of the dose. Co-treatment with mebendazole inhibited anticancer activity of the nitroglycerin and metformin combination. Mebendazole rescued tumor progression suppressed by the combination of nitroglycerin and metformin. Administration of nitroglycerin with metformin might be an effective and safe approach in novel nontoxic adjuvant and relapse prevention anticancer treatment.

The Effect of Topical Tacrolimus on Pedicled Flap Survival

PURPOSE

Skin necrosis is a known postoperative complication of mastectomies. The pathophysiology of tissue necrosis involves lymphatic congestion, followed by venous congestion and ultimately arterial insufficiency. Recent mouse model studies have shown topical tacrolimus to increase growth of lymphatic collateral vessels and decrease lymphedema, potentially obviating the cycle of necrosis and increasing skin survival. The purpose of this study was to investigate the effect of topical tacrolimus on skin flap necrosis in a rat model.

METHODS

A cranially based dorsal skin flap measuring 3 × 10 cm was raised and reinset on 22 Sprague-Dawley rats. They were then randomized to either the control (topical petroleum jelly) or the treatment (topical 0.1% tacrolimus) arm. In addition, 0.2 g of either ointment was spread over the flap and then covered with an occlusive dressing. Dressings were changed daily with reapplication of both the topical ointment and occlusive dressing. The rats were sacrificed 7 days postoperatively; areas of viable tissue, reversible ischemia, and full thickness necrosis were measured with Fiji software, and comparative analysis was performed with GraphPad statistical software.

RESULTS

The average area of the dorsal flaps in the control and tacrolimus groups was 22.5 and 23.9 cm, respectively. In the control cohort, the average viable area was 42.4%, the average reversible ischemia area was 43.6%, and the average necrotic area was 13.9%. In the tacrolimus cohort, the average viable area was 31.5%, the average reversible ischemia area was 59.3%, and the average necrotic area was 9.2%. Total necrotic area was significantly lower in rats receiving topical tacrolimus as compared with controls (P = 0.015). Furthermore, the ratios of necrotic to reversible ischemia and necrotic to viable tissue were significantly lower in the tacrolimus group as compared with controls (P = 0.003, P = 0.015). There was one incidence of wound dehiscence secondary to rodent self-removal of dressings and suture that required reoperation and reinset.

CONCLUSIONS

Topical tacrolimus was associated with significantly less full thickness necrosis as compared with topical.

Subcutaneous Injection of Nitroglycerin at the Radial Artery Puncture Site Reduces the Risk of Early Radial Artery Occlusion After Transradial Coronary Catheterization: A Randomized, Placebo-Controlled Clinical Trial

BACKGROUND

Transradial coronary catheterization is widely used as a diagnostic or interventional procedure for coronary disease. However, it can lead to adverse complications, such as radial artery occlusion. We sought to determine whether preprocedural injection of nitroglycerin at the radial artery puncture site reduces radial artery occlusion.

METHODS AND RESULTS

A total of 188 patients undergoing transradial coronary catheterization were randomized in a single-blind fashion to receive subcutaneous injection of 0.5 mL 0.1% nitroglycerin or a placebo at the radial artery puncture site. The participants underwent ultrasound examinations of the radial artery before and at 24 hours after the procedure. Of the 188 patients enrolled, 182 completed the study, as the procedure failed in 2 participants in the nitroglycerin-treated group and 4 in the placebo group. Baseline demographic and clinical characteristics were similar between 2 groups. Comparing the radial artery diameters before and after the operation, there was a statistically significant increase in the nitroglycerin-treated group (2.48±0.45 versus 2.45±0.46 mm; P=0.003) but a decrease in the placebo control group (2.41±0.50 versus 2.46±0.49 mm; P<0.001). Importantly, the incidence of radial arterial occlusion was substantially lower in the nitroglycerin-treated group than in the placebo control group (5.4% versus 14.4%; P=0.04). There was not significant difference in other complications (forearm hematoma and radial artery pseudoaneurysm, respectively), and there was no incidence of cause hypotension or an intolerable headache.

CONCLUSIONS

Subcutaneous injection of nitroglycerin at the radial artery puncture site dilates the radial artery and reduces the incidence of early radial artery occlusion post-catheterization.

CLINICAL TRIAL REGISTRATION

URL: https://www.chictr.org.cn. Unique identifier: ChiCTR-IPR-15006559.

Recognition and Optimization of Ingredients Treating Nitroglycerin-Induced Migraine Rats from Wuzhuyu Decoction

Wuzhuyu decoction (WZYD) has been clinically used to treat migraine effectively since Eastern Han Dynasty of ancient China. However, its antimigrainic ingredients remain unclear. In present study, the antimigrainic ingredients of WZYD were explored and optimized in nitroglycerin-induced migraine rats through correlation analysis of decoction spectra-pharmacological effects and absorption spectra-pharmacological using entropy-weighted partial least squares regression method. The decoction spectra and absorption spectra were obtained through the determination of nine main ingredients in ten kinds of WZYDs and WZYDs' single-pass intestinal perfusion samples using high performance liquid chromatography-diode array detector. The pharmacodynamics indexes related to migraine model rats were detected using high performance liquid chromatography method and kits after oral administration of WZYDs. Then, the key ingredients influencing indexes were achieved through the correlation analysis. And the optimization of key ingredients was acquired through uniform design experiment. The pharmacodynamic verification test was used to clarify the advantages of the optimized sample. The results showed that the final optimized sample, in which the concentrations of rutaecarpine, evodiamine, ginsendside Rb₁, 6-gingerol, ginsendside Rg₁, rutaevine, and limonin were 0.081, 0.565, 1.455, 0.159, 0.871, 0.178, and 0.009 mg·mL⁻¹, respectively, provided the best comprehensive effect than another optimized sample and the best uniform design sample. Therefore, a new reliable method for rapidly recognizing and optimizing the effective constituents of WZYD treating migraine was established.

Coordinative interaction between nitrogen oxides and iron–molybdenum POM Mo72Fe30

The process of adsorption of nitrogen monoxide and dioxide by the giant Keplerate nanocluster Mo₇₂Fe₃₀ was studied in detail under ambient conditions and air/argon atmosphere.

Perioperative diltiazem or nitroglycerin in on-pump coronary artery bypass: A systematic review and network meta-analysis

Background

Arterial graft spasm is a severe complication after coronary artery bypass graft (CABG). Among numerous potential antispasmodic agents, systemic application of diltiazem and nitroglycerin had been investigated most frequently over the past three decades. However, it remains inconclusive if either or both agents could improve patient outcomes by preventing graft spasm when applied perioperatively, and, if so, which one would be a better choice. The current systematic review and network meta-analysis aims to summarize the data from all available randomized clinical trials of perioperative continuous intravenous infusion of diltiazem and/or nitroglycerin in patients undergoing on-pump CABG in order to define and compare their roles in graft spasm prevention and their impacts on perioperative outcomes.

Methods

We searched Ovid Medline, PubMed, CINAHL, Google Scholar and Cochrane Center for randomized controlled trials that reported outcome effects of perioperative continuous intravenous infusion of diltiazem and/or nitroglycerin in patients undergoing elective on-pump CABG. Conventional meta-analyses were conducted to evaluate the pairwise comparisons (diltiazem vs. placebo; nitroglycerin vs. placebo; diltiazem vs. nitroglycerin) on perioperative outcomes. Network meta-analyses were implemented to compare the three regimens through direct and indirect comparison.

Results

Twenty-seven studies involving 1,660 patients were included. Pairwise and network meta-analyses found no significant difference in mortality among the groups. There are four studies that reported blood flow measurements of internal mammary artery grafts intraoperatively after dissecting or immediately after distal anastomosis while patients were on continuous intravenous infusion of diltiazem and nitroglycerin. Although insufficient for data synthesis, the measured results from all four studies suggest that both diltiazem and nitroglycerin significantly increased blood flow of arterial grafts compared to placebo. For other perioperative outcomes, compared to diltiazem, patients that received nitroglycerin had higher odds of postoperative atrial fibrillation (OR = 2.67, 95% CI: 1.15 to 6.24) and higher peak serum cardiac enzymes. Patients that received placebo had higher odds of atrial fibrillation (OR = 3.00, 95% CI: 1.18 to 7.63) and lower odds of requiring inotrope support (OR = 0.19, 95% CI: 0.04 to 0.73) compared to diltiazem. Data from the network meta-analysis indicated that diltiazem had significantly lower odds of postoperative atrial fibrillation compared to nitroglycerin (OR = 0.39, 95% CI: 0.18 to 0.85). In fact, the rank from highest to lowest rates of postoperative atrial fibrillation was placebo>nitroglycerin>diltiazem. The rank from highest to lowest odds of requiring inotropic support is nitroglycerin> diltiazem>placebo. However, placebo had significantly higher odds of postoperative myocardial infarction than diltiazem (OR = 4.51, 95% CI: 1.34 to 15.25). The rank from highest to lowest odds of postoperative myocardial infarction, transient cardiac ischemic event and atrial fibrillation is placebo>nitroglycerin>diltiazem.

Conclusion

Compared to nitroglycerin and placebo, perioperative continuous intravenous infusion of diltiazem had stronger protective effects against postoperative ischemic cardiac injuries and atrial fibrillation although patients may need more inotropic support. The increased blood flow from diltiazem use in arterial grafts may potentially contribute to the drug’s outcome benefits.

Synthesis and characterization of a novel organic nitrate NDHP: Role of xanthine oxidoreductase-mediated nitric oxide formation

In this report, we describe the synthesis and characterization of 1,3-bis(hexyloxy)propan-2-yl nitrate (NDHP), a novel organic mono nitrate. Using purified xanthine oxidoreductase (XOR), chemiluminescence and electron paramagnetic resonance (EPR) spectroscopy, we found that XOR catalyzes nitric oxide (NO) generation from NDHP under anaerobic conditions, and that thiols are not involved or required in this process. Further mechanistic studies revealed that NDHP could be reduced to NO at both the FAD and the molybdenum sites of XOR, but that the FAD site required an unoccupied molybdenum site. Conversely, the molybdenum site was able to reduce NDHP independently of an active FAD site. Moreover, using isolated vessels in a myograph, we demonstrate that NDHP dilates pre-constricted mesenteric arteries from rats and mice. These effects were diminished when XOR was blocked using the selective inhibitor febuxostat. Finally, we demonstrate that NDHP, in contrast to glyceryl trinitrate (GTN), is not subject to development of tolerance in isolated mesenteric arteries.

Vasodilatory effect of nitroglycerin in Japanese subjects with different aldehyde dehydrogenase 2 (ALDH2) genotypes

The functional genetic polymorphism of aldehyde dehydrogenase 2 (ALDH2) influences the enzymatic activities of its wild type (Glu504 encoded by ALDH2*1) and mutant type (Lys504 encoded by ALDH2*2) proteins. The enzymatic activities of mutant-type ALDH2 are limited compared with those of the wild type. ALDH2 has been suggested as a critical factor for nitroglycerin-mediated vasodilation by some human studies and in vitro studies. Currently, there is no research on direct observations of the vasodilatory effect of nitroglycerin sublingual tablets, which is the generally used dosage form. In the present study, the contribution of ALDH2 to the vasodilatory effect of nitroglycerin sublingual tablets was investigated among three genotype groups (ALDH2*1/*1, ALDH2*1/*2, and ALDH2*2/*2) in Japanese. The results by direct assessments of in vivo nitroglycerin-mediated dilation showed no apparent difference in vasodilation among all genotypes of ALDH2. Furthermore, to analyze the effect of other factors (age and flow-mediated dilation), multiple regression analysis and Pearson's correlation coefficient analysis were carried out. These analyses also indicated that the genotypes of ALDH2 were not related to the degree of vasodilation. These results suggest the existence of other predominant pathway(s) for nitroglycerin biotransformation, at least with regard to clinical nitroglycerin (e.g., a sublingual tablet) in Japanese subjects.

Antispastic Management in Arterial Grafts in Coronary Artery Bypass Grafting Surgery

Arterial grafts have long-term patency superior to vein grafts but have a tendency to develop spasm that can lead to potentially life-threatening complications. A perfect antispastic protocol should include advanced surgical technique and adequate pharmacologic methods. All pharmacologic vasodilator drugs relax the vessel through specific mechanisms, and therefore, there is no perfect, single best vasodilator to prevent or treat spasm of the arterial graft against all mechanisms of contraction. One of the choices is to use a combination of pharmacologic vasodilators targeting different mechanisms of spasm to obtain the reliable and best effect.

Nitric oxide generation by the organic nitrate NDBP attenuates oxidative stress and angiotensin II-mediated hypertension

BACKGROUND AND PURPOSE

NO deficiency and oxidative stress are crucially involved in the development or progression of cardiovascular disease, including hypertension and stroke. We have previously demonstrated that acute treatment with the newly discovered organic nitrate, 2-nitrate-1,3-dibuthoxypropan (NDBP), is associated with NO-like effects in the vasculature. This study aimed to further characterize the mechanism(s) and to elucidate the therapeutic potential in a model of hypertension and oxidative stress.

EXPERIMENTAL APPROACH

A combination of ex vivo, in vitro and in vivo approaches was used to assess the effects of NDBP on vascular reactivity, NO release, NADPH oxidase activity and in a model of hypertension.

KEY RESULTS

Ex vivo vascular studies demonstrated NDBP-mediated vasorelaxation in mesenteric resistance arteries, which was devoid of tolerance. In vitro studies using liver and kidney homogenates revealed dose-dependent and sustained NO generation by NDBP, which was attenuated by the xanthine oxidase inhibitor febuxostat. In addition, NDBP reduced NADPH oxidase activity in the liver and prevented angiotensin II-induced activation of NADPH oxidase in the kidney. In vivo studies showed that NDBP halted the progression of hypertension in mice with chronic angiotensin II infusion. This was associated with attenuated cardiac hypertrophy, and reduced NADPH oxidase-derived oxidative stress and fibrosis in the kidney and heart.

CONCLUSION AND IMPLICATIONS

The novel organic nitrate NDBP halts the progression of angiotensin II-mediated hypertension. Mechanistically, our findings suggest that NDBP treatment is associated with sustained NO release and attenuated activity of NADPH oxidase, which to some extent requires functional xanthine oxidase.

RRx-001, A novel dinitroazetidine radiosensitizer

The ‘holy grail’ in radiation oncology is to improve the outcome of radiation therapy (RT) with a radiosensitizer—a systemic chemical/biochemical agent that additively or synergistically sensitizes tumor cells to radiation in the absence of significant toxicity. Similar to the oxygen effect, in which DNA bases modified by reactive oxygen species prevent repair of the cellular radiation damage, these compounds in general magnify free radical formation, leading to the permanent “fixation” of the resultant chemical change in the DNA structure. The purpose of this review is to present the origin story of the radiosensitizer, RRx-001, which emerged from the aerospace industry. The activity of RRx-001 as a chemosensitizer in multiple tumor types and disease states including malaria, hemorrhagic shock and sickle cell anemia, are the subject of future reviews.

Utility of different outcome measures for the nitroglycerin model of migraine in mice

INTRODUCTION

Majority of the work for establishing nitroglycerin (NTG)-induced migraine models in animals was done in rats, though recently some studies in mice were also reported. Different special formulations of NTG were investigated in various studies; however, NTG treated groups were often compared to simple saline treated control groups. The aim of the present studies was to critically assess the utility of a panel of potential outcome measures in mice by revisiting previous findings and investigating endpoints that have not been tested in mice yet.

METHODS

We investigated two NTG formulations, Nitrolingual and Nitro Pohl, at an intraperitoneal dose of 10mg/kg, in comparison with relevant vehicle controls, and evaluated the following outcome measures: light aversive behaviour, cranial blood perfusion by laser Doppler imaging, number of c-Fos- and neuronal nitrogen monoxide synthase (nNOS)-immunoreactive neurons in the trigeminal nucleus caudalis (TNC) and trigeminal ganglia, thermal hyperalgesia and tactile allodynia of the hind paw and orofacial pain hypersensitivity.

RESULTS

We could not confirm previous reports of significant NTG-induced changes in light aversion and cranial blood perfusion of mice but we observed considerable effects elicited by the vehicle of Nitrolingual. In contrast, the vehicle of Nitro Pohl was apparently inert. Increased c-Fos expression in the TNC, thermal hyperalgesia, tactile allodynia and orofacial hypersensitivity were apparently good endpoints in mice that were increased by NTG-administration. The NTG-induced increase in c-Fos expression was prevented by topiramate but not by sumatriptan treatment. However, the NTG-induced orofacial hypersensitivity was dose dependently attenuated by sumatriptan.

DISCUSSION

Our results pointed to utilisable NTG formulations and outcome measures for NTG-induced migraine models in mice. Pending further cross-validation with positive and negative control drugs in these mouse models and in the human NTG models of migraine, these tests might be valuable translational research tools for development of new anti-migraine drugs.

Nitrite-mediated renal vasodilatation is increased during ischemic conditions via cGMP-independent signaling

The kidney is vulnerable to hypoxia, and substantial efforts have been made to ameliorate renal ischemic injury secondary to pathological conditions. Stimulation of the nitrate-nitrite-nitric oxide pathway is associated with renal and cardiovascular protection in disease models, but less is known about the vascular effects during renal ischemia. This study was aimed at investigating the vascular effects of nitrite in the kidney during normoxic and ischemic conditions. Using a multiwire myograph system, we assessed nitrite-mediated relaxation (10(-9)-10(-4)mol/L) in isolated and preconstricted renal interlobar arteries from C57BL/6 mice under normal conditions (pO2 13kPa; pH 7.4) and with low oxygen tension and low pH to mimic ischemia (pO2 3kPa; pH 6.6). Xanthine oxidoreductase expression was analyzed by quantitative PCR, and production of reactive nitrogen species was measured by DAF-FM DA fluorescence. During normoxia significant vasodilatation (15±3%) was observed only at the highest concentration of nitrite, which was dependent on NO-sGC-cGMP signaling. The vasodilatory responses to nitrite were greatly sensitized and enhanced during hypoxia with low pH, demonstrating significant dilatation (11±1%) already in the physiological range (10(-8)mol/L), with a maximum response of 27±2% at 10(-4) mol/L. In contrast to normoxia, and to that observed with a classical NO donor (DEA NONOate), this sensitization was independent of sGC-cGMP signaling. Moreover, inhibition of various enzymatic systems reported to reduce nitrite in other vascular beds, i.e., aldehyde oxidase (raloxifene), aldehyde dehydrogenase (cyanamide), and NO synthase (L-NAME), had no effect on the nitrite response. However, inhibition of xanthine oxidoreductase (XOR; febuxostat or allopurinol) abolished the sensitized response to nitrite during hypoxia and acidosis. In conclusion, in contrast to normoxia, nitrite exerted potent vasorelaxation during ischemic conditions already at physiological concentrations. This effect was dependent on functional XOR but independent of classical downstream signaling by sGC-cGMP.

New Drugs You Are Going to Read About: Serelaxin, Ularitide, TRV027

Nitrovasodilators have long been used as first-line treatment for hypertensive acute heart failure (AHF). Although effective for BP control and symptom alleviation, this class of agents has never been shown to improve mortality or prevent hospital readmissions. Consequently, there has been tremendous interest in development of newer vasodilators with more beneficial therapeutic profiles. In this review, we focus on three of the most promising agents currently being studied: serelaxin, ularitide, and TRV027. While regulatory approval has yet to be obtained, should they prove beneficial in on-going trials, we are looking at a new era of drug therapy that could supplant more conventional treatments and broaden the horizon for management of patients with AHF.

Low hazard small-scale synthesis and chemical analysis of high purity nitroglycerine (NG)

A two-phase batch method to prepare high purity 1,2,3-propanetriyl trinitrate (nitroglycerine, NG) was evaluated, simplified and adapted specifically for low hazard small-scale synthesis.

Allopurinol prevents nitroglycerin-induced tolerance in rat thoracic aorta

Xanthine oxidase is an important source of reactive oxygen species; so, it may play a role in the pathogenesis of endothelium dysfunction and its consequences. Allopurinol, a purine analog, is a famous xanthine oxidase inhibitor. This study aimed to investigate possible effects of allopurinol on nitroglycerin tolerance, vasoconstriction, and vasorelaxation in rat aortic ring. Using thoracic aortic rings obtained from male Wistar rats, the effect of allopurinol was examined on nitroglycerin-induced tolerance. In addition, changes of vasoconstriction (by using KCl and phenylephrine) and vasorelaxation (by using carbachol, sodium nitroprusside, and nitroglycerin) were also measured and compared between tissues treated with and without allopurinol. All 3 concentrations of allopurinol (50, 100, and 150 μM) significantly acted against the development of nitroglycerin-induced tolerance in comparison with controls. In terms of vasoconstriction and vasorelaxation, the effect of allopurinol was significant only on carbachol-induced (endothelium related) vasorelaxation in a dose-dependent manner. In conclusion, although allopurinol had no significant effect on the contractile response of the aorta, in accord with the previous data, it significantly intensified endothelium-dependent vasodilation. The inhibitory effect of allopurinol against the development of nitrate-induced tolerance may suggest its clinical benefit and is worth to be studied more extensively.

The efficacy and hemodynamic response to Dexmedetomidine as a hypotensive agent in posterior fixation surgery following traumatic spine injury

AIM

This study was designed to evaluate the efficacy of dexmedetomidine (DEX) as a hypotensive agent in comparison to nitroglycerin (NTG) in posterior fixation surgery for traumatic spine injury.

MATERIALS AND METHODS

Forty patients ASA I or II aged 18-65 years scheduled for posterior fixation surgery were randomly assigned to receive either DEX 1 μg/kg over 10 min before induction of anesthesia followed by 0.2-0.7 μg/kg/h infusion during maintenance in DEX group or NTG 3-5 μg/kg/min infusion after induction of anesthesia in NTG group to maintain mean arterial blood pressure (MAP) between 65 and 70 mmHg. The two groups were compared for achievement of target MAP, intraoperative blood loss, and reversibility of hypotensive state. Student's t-test was used for continuous variables and chi-square test for categorical variables. P-value < 0.05 was considered significant.

RESULTS

Patients in DEX group achieved the target MAP with better heart rate (HR) control, as compared to NTG group during the period of observation. The blood loss was significantly lesser in the DEX group (422.11 ± 149.34 ml) than the NTG group (564.51 ± 160.88 ml), P = 0.01. The time to hypotension reversal in NTG group (5.63 ± 1.93 min) was lesser compared to DEX group (9.15 ± 2.16 min), P = 0.65.

CONCLUSION

DEX is an effective and safe agent in achieving controlled hypotension in adults undergoing posterior fixation spine surgery.

Vasodilators in Acute Heart Failure: Review of the Latest Studies

Vasodilators play an important role in the management of acute heart failure, particularly when increased afterload is the precipitating cause of decompensation. The time-honored approach to afterload reduction has been largely focused on use of intravenous nitrovasodilators and, when properly dosed, this class of agents does provide substantial symptom relief for patients with acute hypertensive heart failure. Despite this, nitrovasodilators have never been shown to diminish mortality or provide any post-discharge outcome benefit leading to an on-going search for viable and more effective alternatives. While no new vasodilators have been approved for use in acute heart failure since nesiritide more than a decade ago, a number of novel agents have been developed, with some showing significant promise in recent clinical trials. In this review, we summarize the latest study data as it relates to vasodilator therapy and provide a glimpse into the not too distant future state of acute heart failure care.

Sex differences in cardiovascular drug-induced adverse reactions causing hospital admissions

AIMS

Cardiovascular disease in women is often underestimated. The effects of cardiovascular drugs differ between the sexes because of pharmacokinetic and pharmacodynamic differences. Adverse drug reactions (ADRs) within these drug classes may have serious consequences, leading to hospital admission. We aimed to study differences between men and women in hospital admissions for ADRs due to cardiovascular drugs.

METHODS

We conducted a nationwide study of all hospital admissions between 2000 and 2005 with data from the Dutch National Medical Register. Relative risks were calculated of hospital admissions due to ADRs to the different cardiovascular drug groups for women compared with men. By an ecological design, risks were adjusted for the total number of Dutch inhabitants and the total number of prescriptions.

RESULTS

In total, 14 207 of the hospital admissions (34% of all ADR-related admissions) were attributed to cardiovascular drugs [7690 in women (54%; 95% confidence interval 53-55%)]. 'Anticoagulants and salicylates' (n= 8988), 'high- and low-ceiling diuretics' (n= 2242) and 'cardiotonic glycosides' (n= 932) were responsible for the majority of the ADR-related hospital admissions. The most pronounced sex differences were seen in users of low-ceiling diuretics (relative risk 4.02; 95% confidence interval 3.12-5.19), cardiotonic glycosides (relative risk 2.38; 95% confidence interval 2.06-2.74), high-ceiling diuretics (relative risk 2.10; 95% confidence interval 1.91-2.32) and coronary vasodilators (relative risk 0.77; 95% confidence interval 0.65-0.91).

CONCLUSIONS

Clear sex differences exist in ADRs requiring hospital admission for different cardiovascular drug groups. Sex differences should be taken into account in the prescription and evaluation of drugs.

Simultaneous determination of three alkaloids, four ginsenosides and limonin in the plasma of normal and headache rats after oral administration of Wu-Zhu-Yu decoction by a novel ultra fast liquid chromatography-tandem mass spectrometry method: application to a comparative pharmacokinetics and ethological study

A novel, sensitive and reliable ultra fast liquid chromatography-tandem mass spectrometry (UFLC-MS/MS) method has been developed and validated for simultaneous quantitation of eight main active ingredients (evodiamine, rutaecarpine, dehydroevodiamine, limonin, ginsenoside Rb1, Rd, Re and Rg1) in rat plasma after oral administration of Wu-Zhu-Yu (WZY) decoction, which is a celebrated and widely used Traditional Chinese Medicine formula for the treatment of headache. The analytes and internal standard (IS) were separated on a SHIM-PACK XR-ODS II column, and the detection was performed on a UFLC-MS/MS system with turbo ion spray source. The lower limits of quantification were 1.5, 0.5, 1.0, 2.0, 2.0, 1.0, 0.5 and 0.2 ng ml(-1) for evodiamine, rutaecarpine, dehydroevodiamine, limonin, gensenoside Rb1, Rd, Re and Rg1, respectively. Linearity, accuracy, precision and absolute recoveries of the eight analytes were all within satisfaction. The IS-normalized matrix factor was adopted for assessing the matrix effect and accompanied with a satisfactory result. The validated method has been successfully applied to compare pharmacokinetic profiles of the eight active ingredients in rat plasma between normal and headache rats after administration. Exact pharmaceutical effect of WZY decoction on headache was demonstrated by the ethological response of headache rats induced by nitric oxide donor after administration. The results indicated that the absorption of evodiamine, rutaecarpine, gensenoside Rb1, Re and Rg1 in headache group were significantly higher than those in normal group with similar concentration-time curves while no significant differences existed in limonin and ginsenoside Rd between the two groups.

Acute Heart Failure Treatment

Dyspnea is the predominant symptom for patients with acute heart failure and initial treatment is largely directed towards the alleviation of this. Contrary to conventional belief, not all patients present with fluid overload and the approach to management is rapidly evolving from a solitary focus on diuresis to one that more accurately reflects the complex interplay of underlying cardiac dysfunction and acute precipitant. Effective treatment thus requires an understanding of divergent patient profiles and an appreciation of various therapeutic options for targeted patient stabilization. The key principle within this paradigm is directed management that aims to diminish the work of breathing through situation appropriate ventillatory support, volume reduction and hemodynamic improvement. With such an approach, clinicians can more efficiently address respiratory discomfort while reducing the likelihood of avoidable harm.

Optimizing drug therapy in the surgical intensive care unit

This article provides a review of commonly prescribed medications in the surgical ICU, focusing on sedatives, antipsychotics, neuromuscular blocking agents, cardiovascular agents, anticoagulants, and antibiotics. A brief overview of pharmacology is followed by practical considerations to aid prescribers in selecting the best therapy within a given category of drugs to optimize patient outcomes.

Nitrite and nitrite reductases: from molecular mechanisms to significance in human health and disease

Nitrite, previously considered physiologically irrelevant and a simple end product of endogenous nitric oxide (NO) metabolism, is now envisaged as a reservoir of NO to be activated in response to oxygen (O(2)) depletion. In the first part of this review, we summarize and compare the mechanisms of nitrite-dependent production of NO in selected bacteria and in eukaryotes. Bacterial nitrite reductases, which are copper or heme-containing enzymes, play an important role in the adaptation of pathogens to O(2) limitation and enable microrganisms to survive in the human body. In mammals, reduction of nitrite to NO under hypoxic conditions is carried out in tissues and blood by an array of metalloproteins, including heme-containing proteins and molybdenum enzymes. In humans, tissues play a more important role in nitrite reduction, not only because most tissues produce more NO than blood, but also because deoxyhemoglobin efficiently scavenges NO in blood. In the second part of the review, we outline the significance of nitrite in human health and disease and describe the recent advances and pitfalls of nitrite-based therapy, with special attention to its application in cardiovascular disorders, inflammation, and anti-bacterial defence. It can be concluded that nitrite (as well as nitrate-rich diet for long-term applications) may hold promise as therapeutic agent in vascular dysfunction and ischemic injury, as well as an effective compound able to promote angiogenesis.

Nitric oxide modulation as a therapeutic strategy in heart failure

Nitric oxide (NO) is recognized as one of the most important cardiovascular signaling molecules, with multiple regulatory effects on myocardial and vascular tissue as well as on other tissues and organ systems. With the growth in understanding of the range and mechanisms of NO effects on the cardiovascular system, it is now possible to consider pharmaceutical interventions that directly target NO or key steps in NO effector pathways. This article reviews aspects of the cardiovascular effects of NO, abnormalities in NO regulation in heart failure, and clinical trials of drugs that target specific aspects of NO signaling pathways.

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.

Is nitric oxide a hormone?

Nitric oxide (NO) is a simple ubiquitous signaling molecule and plays important roles in almost every biological system. Recent evidences suggest that NO may act as an endocrine molecule. The aim of this review is considering available literature on endocrine roles of NO and/or its metabolites, i.e. nitrite and nitrate. Existing data suggest the idea that NO is a hormone that after production in tissues, it is stabilized and transported as nitrite and/or S-nitrosothiols in the blood to target cells.

Daily low-dose folic acid supplementation does not prevent nitroglycerin-induced nitric oxide synthase dysfunction and tolerance: a human in vivo study

INTRODUCTION

Continuous treatment with nitroglycerin (GTN) causes tolerance and endothelial dysfunction, both of which may involve endothelial nitric oxide synthase (eNOS) dysfunction. eNOS dysfunction may be linked to depletion of tetrahydrobiopterin, and folic acid may be involved in the regeneration of this cofactor. It has been demonstrated that 10 mg⁄day folic acid supplementation prevents the development of GTN tolerance and GTN-induced endothelial dysfunction. However, the efficacy of daily lower-dose folic acid supplementation for preventing these phenomena has not been investigated.

OBJECTIVE

To determine the effect of 1 mg⁄day folic acid supplementation on responses to sustained GTN therapy.

METHODS AND RESULTS

On visit 1, 20 healthy male volunteers were randomly assigned to receive either oral folic acid (1 mg⁄day) or placebo for one week in a double- blind study. All subjects also received continuous transdermal GTN (0.6 mg⁄h). On visit 2, forearm blood flow was measured using venous occlusion strain-gauge plethysmography in response to incremental intra-arterial infusions of acetylcholine, N-monomethyl-L-arginine and GTN. Subjects in both groups displayed significantly decreased responses to acetylcholine and N-monomethyl-L-arginine infusions compared with a control group that received no treatment. Responses to GTN were also significantly diminished in both groups (P<0.05 for all).

DISCUSSION

The present data demonstrate that daily supplementation with 1 mg folic acid does not prevent the development of GTN-induced eNOS dysfunction or tolerance.

Mitochondrial aldehyde dehydrogenase mediates vasodilator responses of glyceryl trinitrate and sodium nitrite in the pulmonary vascular bed of the rat

It has been reported that mitochondrial aldehyde dehydrogenase (ALDH2) catalyzes the formation of glyceryl dinitrate and inorganic nitrite from glyceryl trinitrate (GTN), leading to an increase in cGMP and vasodilation in the coronary and systemic vascular beds. However, the role of nitric oxide (NO) formed from nitrite in mediating the response to GTN in the pulmonary vascular bed is uncertain. The purpose of the present study was to determine if nitrite plays a role in mediating vasodilator responses to GTN. In this study, intravenous injections of GTN and sodium nitrite decreased pulmonary and systemic arterial pressures and increased cardiac output. The decreases in pulmonary arterial pressure under baseline and elevated tone conditions and decreases in systemic arterial pressure in response to GTN and sodium nitrite were attenuated by cyanamide, an ALDH2 inhibitor, whereas responses to the NO donor, sodium nitroprusside (SNP), were not altered. The decreases in pulmonary and systemic arterial pressure in response to GTN and SNP were not altered by allopurinol, an inhibitor of xanthine oxidoreductase, whereas responses to sodium nitrite were attenuated. GTN was approximately 1,000-fold more potent than sodium nitrite in decreasing pulmonary and systemic arterial pressures. These results suggest that ALDH2 plays an important role in the bioactivation of GTN and nitrite in the pulmonary and systemic vascular beds and that the reduction of nitrite to vasoactive NO does not play an important role in mediating vasodilator responses to GTN in the intact chest rat.

Microwave-assisted hydrolysis of nitroglycerin (NG) under mild alkaline conditions: new insight into the degradation pathway

Nitroglycerin (NG), a nitrate ester, is widely used in the pharmaceutical industry and as an explosive in dynamite and as propellant. Currently NG is considered as a key environmental contaminant due to the discharge of wastewater tainted with the chemical from the military and pharmaceutical industry. The present study describes hydrolytic degradation of NG (200 microM) at pH 9 using either conventional or microwave-assisted heating at 50 degrees C. We found that hydrolytic degradation of NG inside the microwave chamber was much higher than its degradation using conventional heating. Products distributions in both heating systems were closely related and included nitrite, nitrate, formic acid, and the novel intermediates 2-hydroxypropanedial (OCHCH(OH)HCO) and glycolic acid (CH2(OH)COOH). Two other intermediates glycolaldehyde (CH2(OH)CHO) and glyoxylic acid (CHOCOOH) were only detected in the microwave treated samples. The molar ratio of nitrite to nitrate in the presence and absence of microwave heating was 2.5 and 2.8, respectively. In both microwave assisted and conventional heating a nitrogen mass balance of 96% and 98% and a carbon mass balance of 58% and 78%, respectively, were obtained. The lower C mass recovery might be attributed to further unknown reactions, e.g., polymerization of the aldehydes CH2(OH)CHO, CHOCOOH and OCHCH(OH)HCO. A hydrolytic degradation pathway for NG was proposed involving denitration (loss of 2 NO2(-)) from the two primary carbons and the loss of one nitrate from the secondary carbon to produce 2-hydroxypropanedial.

Nitroglycerin headache and nitroglycerin-induced primary headaches from 1846 and onwards: a historical overview and an update

Nitroglycerin (NTG) (glyceryl trinitrate) was synthesized by the Italian chemist Ascanio Sobrero in Paris in 1846. A very unstable explosive, Alfred Nobel while working on explosives, combined it with Kiselguhr and patented it as dynamite in 1867. NTG was introduced in 1879 in medicine in the treatment of angina pectoris by the English doctor William Murrell. NTG-induced headache was quickly recognized as an important adverse event both in the industrial use of NTG, where it was used to produce dynamite, as well as in the use of NTG as drug. This review traces the evolution of our understanding of NTG headache.

NO and sGC-stimulating NO donors

Our knowledge of nitric oxide (NO) as a crucial endogenous signalling molecule continues to expand. Many, but not all, of the actions of NO are mediated by activation of soluble guanylyl cyclase (sGC) in target tissues. The aim of this chapter is to encapsulate the functions of NO in mammalian biology, tied to the chemistry of this unusual signalling entity. The experimental usefulness and therapeutic potential of the most widely utilised NO donor drugs is reviewed, with special consideration given to the importance of choosing the correct NO donor for any given experiment, in vitro, in vivo or in clinical studies.

Effect of intravenous nitroglycerin therapy on erythrocyte antioxidant enzymes

Intravenous nitroglycerin (GTN) has been used as an anti-ischemic agent for the therapy of unstable and post-infarction angina. Nitric oxide (NO) and S-nitrosothiols constitute the biologically active species formed via nitroglycerin bioactivation. Increased levels of reactive oxygen species can diminish the therapeutic action of organic nitrates by scavenging donated NO and oxidizing tissue thiols important in nitrate biotransformation. Studies reported here show that the red cell activity of antioxidant enzymes, catalase and glutathione peroxidase, are significantly decreased after intravenous nitroglycerin treatment. Catalase activity (739.6 +/- 92.3 k/gHb) decreased to 440.1 +/- 111.9 and 459.8 +/- 130.7 k/gHb after 1 and 24 hr GTN infusion, respectively. Similarly, glutathione peroxidase activity (5.8 +/- 1.8 U/gHb) decreased to 3.2 +/- 1.7 and 3.8 +/- 1.1 U/g Hb after 1 and 24 hr GTN infusion, respectively. The reported decrease in antioxidant enzyme activities can lead to an oxidant milieu and contribute to the generation of nitrate tolerance.