Nitric oxide donor drugs: an update on pathophysiology and therapeutic potential

A nanocomposite hydrogel for co-delivery of multiple anti-biofilm therapeutics to enhance the treatment of bacterial biofilm-related infections

The characteristics of biofilms have exacerbated the issue of clinical antibiotic resistance, rendering it a pressing challenge in need of resolution. The combination of biofilm-dispersing agents and antibiotics can eliminate biofilms and promote healing synergistically in infected wounds. In this study, we developed a novel nanocomposite hydrogel (NC gel) comprised of the poly(lactic acid)-hyperbranched polyglycerol (PLA-HPG) based bioadhesive nanoparticles (BNPs) and a hydrophilic carboxymethyl chitosan (CS) network. The NC gel was designed to co-deliver two biofilm-dispersing agents (an NO-donor SNO, and an α-amylase Am) and an antibiotic, cefepime (Cef), utilizing a synergistic anti-biofilm mechanism in which Am loosens the matrix structure and NO promotes the release of biofilm bacteria via quorum sensing, and Cef kills bacteria. The drug-loaded NC gel (SNO/BNP/CS@Am-Cef) demonstrated sustained drug release, minimal cytotoxicity, and increased drug-bacterial interactions at the site of infection. When applied to mice infected with methicillin-resistant Staphylococcus aureus (MRSA) biofilms in vivo, SNO/BNP/CS@Am-Cef enhanced biofilm elimination and promoted wound healing compared to traditional antibiotic treatments. Our work demonstrates the feasibility of the co-delivery of biofilm-dispersing agents and antibiotics using the NC gel and presents a promising approach for the polytherapy of bacterial biofilm-related infections.

Nitroprusside─Expanding the Potential Use of an Old Drug Using Nanoparticles

For more than 70 years, sodium nitroprusside (SNP) has been used to treat severe hypertension in hospital emergency settings. During this time, a few other clinical uses have also emerged such as in the treatment of acute heart failure as well as improving mitral incompetence and in the intra- and perioperative management during heart surgery. This drug functions by releasing nitric oxide (NO), which modulates several biological processes with many potential therapeutic applications. However, this small molecule has a short lifetime, and it has been administered through the use of NO donor molecules such as SNP. On the other hand, SNP also has some setbacks such as the release of cyanide ions, high water solubility, and very fast NO release kinetics. Currently, there are many drug delivery strategies that can be applied to overcome many of these limitations, providing novel opportunities for the use of old drugs, including SNP. This Perspective describes some nitroprusside properties and highlights new potential therapeutic uses arising from the use of drug delivery systems, mainly silica-based nanoparticles. There is a series of great opportunities to further explore SNP in many medical issues as reviewed, which deserves a closer look by the scientific community.

Nicorandil mitigates amiodarone-induced pulmonary toxicity and fibrosis in association with the inhibition of lung TGF-β1/PI3K/Akt1-p/mTOR axis in rats

The long-term side effect of the antiarrhythmic drug, amiodarone (AMIO), such as lung toxicity, remains a critical clinical issue. The previous knowledge denotes diverse antioxidant, anti-inflammatory, and antifibrotic properties of the anti-anginal drug, nicorandil (NI). Therefore, we aimed to investigate the possible protective effect of NI on pulmonary tissue remodelling following AMIO-induced lung toxicity. The included rats were assigned into four equal groups (n = 8): (1) control, (2) control group that received NI 10 mg kg^-1  day^-1 , (3) model group that received AMIO in a dose of 60 mg kg^-1  day^-1 , and (4) treated group (AMIO-NI) that were treated with AMIO plus NI as shown above. Drug administration continued for 10 weeks. AMIO resulted in deteriorated (p < 0.001) pulmonary functions accompanied by respiratory acidosis. AMIO showed an obvious histological injury score with intense collagen deposition, disturbed nitric oxide synthase enzymes (NOS/iNOS), and increased alpha smooth muscle actin expression. Furthermore, AMIO upregulated the transforming growth factor (TGF-β1)/phosphoinositide-3 kinase (PI3K)-Akt1-p/mammalian target of rapamycin (mTOR) axis, which determined the possible mechanism of AMIO on pulmonary remodelling. NI treatment significantly (p < 0.001) prevented the AMIO-induced lung toxicity, as well as inhibited the TGF-β1/PI3K/Akt1-p/mTOR axis in the lung tissue of rats. The results were confirmed by an in-vitro study. CONCLUSION: The current results revealed that NI was effective in preserving the lung structure and functions. Amelioration of the oxidative stress and modulation of TGF-β1/PI3K/Akt1-p/mTOR have been achieved. This study suggests NI administration as a preventive therapy from the serious pulmonary fibrosis side effect of AMIO.

Nebivolol: an effective option against long-lasting dyspnoea following COVID-19 pneumonia - a pivotal double-blind, cross-over controlled study

Background

Pulmonary microvascular occlusions can aggravate SARS-CoV-2 pneumonia and result in a variable decrease in capillary blood volume (Vc). Dyspnoea may persist for several weeks after hospital discharge in many patients who have "radiologically recovered" from COVID-19 pneumonia. Dyspnoea is frequently "unexplained" in these cases because abnormalities in lung vasculature are understudied. Furthermore, even when they are identified, therapeutic options are still lacking in clinical practice, with nitric oxide (NO) supplementation being used only for severe respiratory failure in the hospital setting. Nebivolol is the only selective β¹ adrenoceptor antagonist capable of inducing nitric oxide-mediated vasodilation by stimulating endothelial NO synthase via β₃ agonism. The purpose of this study was to compare the effect of nebivolol versus placebo in patients who had low Vc and complained of dyspnoea for several weeks after COVID-19 pneumonia.

Methods

Patients of both genders, aged ≥18 years, non-smokers, who had a CT scan that revealed no COVID-related parenchymal lesions but still complaining of dyspnoea 12-16 weeks after hospital discharge, were recruited. Spirometrical volumes, blood haemoglobin, SpO₂, simultaneous diffusing capacity for carbon monoxide (CO) and NO (DL_CO and DL_NO, respectively), DL_NO/DL_CO ratio, Vc and exhaled NO (eNO) were measured together with their dyspnoea score (DS), heart frequency (HF), and blood arterial pressure (BAP). Data were collected before and one week after both placebo (P) and nebivolol (N) (2.5 mg od) double-blind cross-over administered at a two-week interval. Data were statistically compared, and p<0.05 assumed as statistically significant.

Results

Eight patients (3 males) were investigated. In baseline, their mean DS was 2.5±0.6 SD, despite the normality of lung volumes. DL_CO and DL_NO mean values were lower than predicted, while mean DL_NO/DL_CO ratio was higher. Mean Vc proved substantially reduced. Placebo did not modify any variable (all p=ns) while N improved DLco and Vc significantly (+8.5%, p<0.04 and +17.7%, p<0.003, respectively). eNO also was significantly increased (+17.6%, p<0.002). Only N lowered the dyspnoea score (-76%, p<0.001). Systolic and diastolic BAP were slightly lowered (-7.5%, p<0.02 and -5.1%, p<0.04, respectively), together with HF (-16.8%, p<0.03).

Conclusions

The simultaneous assessment of DL_NO, DL_CO, DL_NO/DL_CO ratio, and Vc confirmed that long-lasting dyspnoea is related to hidden abnormalities in the lung capillary vasculature. These abnormalities can persist even after the complete resolution of parenchymal lesions regardless of the normality of lung volumes. Nebivolol, but not placebo, improves DS and Vc significantly. The mechanism suggested is the NO-mediated vasodilation via the β3 adrenoceptor stimulation of endothelial NO synthase. This hypothesis is supported by the substantial increase of eNO only assessed after nebivolol. As the nebivolol tolerability in these post-COVID normotensive patients was very good, the therapeutic use of nebivolol against residual and symptomatic signs of long-COVID can be suggested in out-patients.

External stimuli-responsive gasotransmitter prodrugs: Chemistry and spatiotemporal release

Gasotransmitters like nitric oxide, carbon monoxide, and hydrogen sulfide with unique pleiotropic pharmacological effects in mammals are an emerging therapeutic modality for different human diseases including cancer, infection, ischemia-reperfusion injuries, and inflammation; however, their clinical translation is hampered by the lack of a reliable delivery form, which delivers such gasotransmitters to the action site with precisely controlled dosage. The external stimuli-responsive prodrug strategy has shown tremendous potential in developing gasotransmitter prodrugs, which affords precise temporospatial control and better dose control compared with endogenous stimuli-sensitive prodrugs. The promising external stimuli employed for gasotransmitter activation range from photo, ultrasound, and bioorthogonal click chemistry to exogenous enzymes. Herein, we highlight the recent development of external stimuli-mediated decaging chemistry for the temporospatial delivery of gasotransmitters including nitric oxide, carbon monoxide, hydrogen sulfide and sulfur dioxide, and discuss the pros and cons of different designs.

Hypothesis: The potential therapeutic role of nicorandil in COVID-19

At present, there is yet no specific antiviral treatment or immunization against the newly identified human severe acute respiratory syndrome virus (SARS‐CoV2) that results in a rapidly progressive pandemic coronavirus disease 2019 (COVID‐19). We believe in a crucial need for a clinical strategy to counteract this viral pandemic based on the known pathogenesis throughout the disease course. Evidence suggests that exaggerated patient's inflammatory response and oxidative stress are likely to aggravate the disease pathology. The resulting endothelial dysfunction further induces fibrosis and coagulopathy. These disturbances can generate severe acute respiratory distress syndrome (ARDS) that can progress into respiratory and circulatory failure. Nicorandil is an anti‐anginal vasodilator drug acts by increasing nitric oxide bioavailability and opening of the K_ATP channel. Recently, nicorandil has been recognized to possess multiple protective effects against tissue injury. Here, we address a possible modulatory role of nicorandil against COVID‐19 pathogenesis. We hypothesise nicorandil would be an effective form of adjuvant therapy against COVID‐19.

Nitric Oxide (NO) and NO Synthases (NOS)-Based Targeted Therapy for Colon Cancer

Colorectal cancer (CRC) is one of the most lethal malignancies worldwide and CRC therapy remains unsatisfactory. In recent decades, nitric oxide (NO)-a free-radical gas-plus its endogenous producer NO synthases (NOS), have attracted considerable attention. NO exerts dual effects (pro- and anti-tumor) in cancers. Endogenous levels of NO promote colon neoplasms, whereas exogenously sustained doses lead to cytotoxic functions. Importantly, NO has been implicated as an essential mediator in many signaling pathways in CRC, such as the Wnt/β-catenin and extracellular-signal-regulated kinase (ERK) pathways, which are closely associated with cancer initiation, metastasis, inflammation, and chemo-/radio-resistance. Therefore, NO/NOS have been proposed as promising targets in the regulation of CRC carcinogenesis. Clinically relevant NO-donating agents have been developed for CRC therapy to deliver a high level of NO to tumor sites. Notably, inducible NOS (iNOS) is ubiquitously over-expressed in inflammatory-associated colon cancer. The development of iNOS inhibitors contributes to targeted therapies for CRC with clinical benefits. In this review, we summarize the multifaceted mechanisms of NO-mediated networks in several hallmarks of CRC. We review the clinical manifestation and limitations of NO donors and NOS inhibitors in clinical trials. We also discuss the possible directions of NO/NOS therapies in the immediate future.

Emerging drugs to target lower urinary tract symptomatology (LUTS)/benign prostatic hyperplasia (BPH): focus on the prostate

OBJECTIVES

The benign prostatic syndrome, comprising lower urinary tract symptomatology secondary to benign prostatic hyperplasia/enlargement, represents a major health care issue in westernized countries. The pharmacological management involves alpha-adrenoceptor antagonists, intervention into the hormonal control of prostate growth using inhibitors of the enzyme 5-alpha-reductase, and stimulation of the nitric oxide/cyclic GMP pathway by tadalafil, an inhibitor of the phosphodiesterase type 5.

METHODS

This review summarizes the achievements which have been made in the development of drug candidates assumed to offer opportunities as beneficial treatment options in the management of the benign prostatic syndrome.

RESULTS

A review of the literature has revealed that the line of development is focusing on drugs interfering with peripheral neuromuscular/neuronal mechanisms (nitric oxide donor drugs, agonists/antagonists of endogenous peptides, botulinum toxin, NX-1207), the steroidal axis (cetrorelix) or the metabolic turn-over (lonidamine), as well as the combination of drugs already established in the treatment of lower urinary tract symptomatology/benign prostatic hyperplasia (phosphodiesterase 5 inhibitor plus alpha-adrenoceptor antagonist).

CONCLUSION

Many research efforts have provided the basis for the development of new therapeutic modalities for the management of lower urinary tract dysfunctions, some of which might be offered to the patients in the near future.

Anti-CD24 Antibody-Nitric Oxide Conjugate Selectively and Potently Suppresses Hepatic Carcinoma

Nitric oxide (NO) has a wide range of potential applications in tumor therapy. However, a targeted delivery system for NO donors has remained elusive, creating a bottleneck that limits its druggability. The antibody-drug conjugate (ADC) is a targeted drug delivery system composed of an antibody linked to an active cytotoxic drug. This design may compensate for the weak targeting ability and various biological functions of the NO donor. In this study, we designed the NO donor HL-2, which had a targeted, cleaved disulfide bond and an attachable maleimide terminal. We conjugated HL-2 with an antibody that targeted CD24 through a thioether bond to generate an ADC-like immunoconjugate, antibody-nitric oxide conjugate (ANC), which we named HN-01. HN-01 showed efficient internalization and significantly increased the release of NO in hepatic carcinoma cells in vitro. HN-01 induced apoptosis of tumor cells and suppressed tumor growth in hepatic carcinoma-bearing nude mice through antibody-dependent co-toxicity; HN-01 also increased NO levels in tumor cells. Collectively, this study expands the concept of ADC and provides an innovative NO donor and ANC to address current challenges in targeted delivery of NO. This new inspiration for an ANC design can also be used in future studies for other molecules with intracellular targets. SIGNIFICANCE: This study is the first to expand the concept of ADC with an antibody-nitric oxide conjugate that suppresses hepatic carcinoma in vitro and in vivo.

808 nm-light-excited upconversion nanoprobe based on LRET for the ratiometric detection of nitric oxide in living cancer cells

NO (nitric oxide) has dual functions in cancer, promoting carcinogenesis in low concentrations and inducing tumor cell apoptosis at high concentrations. The dual-edged-sword functions of NO make it particularly appealing to develop a sensitive and specific chemical probe for its detection. However, most NO sensors suffer from poor Stokes shifts and are limited by ultraviolet (UV) or visible light excitation, which render it difficult to avoid the intrinsic background signal. In this study, an 808 nm laser-excited Nd³⁺-sensitized upconversion nanoprobe based on LRET (luminescence resonance energy-transfer) for NO detection was constructed for the first time. This probe was composed of Nd³⁺-sensitized core-shell upconversion nanoparticles (540 nm and 660 nm emission) as the energy donor and RhBs as the acceptor. In the presence of NO, RhBs was converted into Rhodamine B and its strong absorption subsequently quenched the 540 nm fluorescence of UCNPs, while the emission at 660 nm remained constant. The ratiometric detection of the fluorescence at 540 nm, as compared to 660 nm, can precisely respond to the difference in NO levels with a detection limit of 0.21 μM. Importantly, compared with conventional UCNPs excited at 980 nm, the 808 nm light excitation led to lower water absorption and deeper tissue penetration, thus avoiding overheating and allowing for long-term biological imaging. This strategy has been perfectly applied to detecting the NO levels in living cells to differentiate the tumor cells from normal cells based on varied intracellular NO concentration. Further, the nanosystem realized the real-time monitoring of NO during treatment with NO donor drugs, which could inspire the future application of this probe to guide NO therapy.

New 4-aryl-1,3,2-oxathiazolylium-5-olates: Chemical synthesis and photochemical stability of a novel series of S-nitrosothiols

S-nitrosothiols (RSNOs) remain one of the most popular classes of NO-donating compounds due to their ability to release nitric oxide (NO) under non-enzymatic means whilst producing an inert disulphide by-product. However, alligning these compounds to the different biological fields of NO research has proved to be problematic due to the inherent instability of such compounds under a variety of conditions including heat, light and the presence of copper ions. 1,3,2-Oxathiazolylium-5-olates (OZOs) represent an interesting subclass of S-nitrosothiols that lock the -SNO moiety into a five membered heterocyclic ring in an attempt to improve the compound's overall stability. The synthesis of a novel series of halogen-containing OZOs was comprehensively studied resulting in a seven-step route and overall yields ranging between 21 and 37%. The photochemical stability of these compounds was assessed to determine if S-nitrosothiols locked within these mesoionic ring systems can offer greater stability and thereby release NO in a more controllable fashion than their non-cyclic counterparts.

Impact of novel N-aryl piperamide NO donors on NF-κB translocation in neuroinflammation: rational drug-designing synthesis and biological evaluation

NO donor drugs showed a significant therapeutic effect in the treatment of many diseases, such as arteriopathies, various acute and chronic inflammatory conditions, and several degenerative diseases. NO-releasing anti-inflammatory drugs are the prototypes of a novel class of compounds, combining the pharmacological activities of anti-inflammatory and anti-nociceptive of drugs with those of NO, thus possessing potential therapeutic applications in a great variety of diseases. In this study, we designed and predicted biological activity by targeting cyclooxygenase type 2 (COX-2) and NF-κB subunits and pharmacological profiling along with toxicity predictions of various N-aryl piperamides linked via an ester bond to a spacer that is bound to a NO-releasing moiety (-ONO2). The result of absorption, distribution, metabolism and excretion and Docking studies indicated that among 51 designed molecules PA-3′K showed the best binding potential in both the substrate and inhibitory binding pocket of the COX-2 enzyme with affinity values of –9.33 and –5.12 for PDB ID 1CVU and 3LN1, respectively, thereby having the potential to be developed as a therapeutic agent. The results of cell viabilities indicated that PA-3′k possesses the best cell viability property with respect to its dose (17.33 ng/ml), with 67.76% and 67.93% viable cells for CHME3 and SVG cell lines, respectively.

Potential therapeutic action of nitrite in sickle cell disease

Sickle cell disease is caused by a mutant form of hemoglobin that polymerizes under hypoxic conditions, increasing rigidity, fragility, calcium influx-mediated dehydration, and adhesivity of red blood cells. Increased red cell fragility results in hemolysis, which reduces nitric oxide (NO) bioavailability, and induces platelet activation and inflammation leading to adhesion of circulating blood cells. Nitric Oxide inhibits adhesion and platelet activation. Nitrite has emerged as an attractive therapeutic agent that targets delivery of NO activity to areas of hypoxia through bioactivation by deoxygenated red blood cell hemoglobin. In this study, we demonstrate anti-platelet activity of nitrite at doses achievable through dietary interventions with comparison to similar doses with other NO donating agents. Unlike other NO donating agents, nitrite activity is shown to be potentiated in the presence of red blood cells in hypoxic conditions. We also show that nitrite reduces calcium associated loss of phospholipid asymmetry that is associated with increased red cell adhesion, and that red cell deformability is also improved. We show that nitrite inhibits red cell adhesion in a microfluidic flow-channel assay after endothelial cell activation. In further investigations, we show that leukocyte and platelet adhesion is blunted in nitrite-fed wild type mice compared to control after either lipopolysaccharide- or hemolysis-induced inflammation. Moreover, we demonstrate that nitrite treatment results in a reduction in adhesion of circulating blood cells and reduced red blood cell hemolysis in humanized transgenic sickle cell mice subjected to local hypoxia. These data suggest that nitrite is an effective anti-platelet and anti-adhesion agent that is activated by red blood cells, with enhanced potency under physiological hypoxia and in venous blood that may be useful therapeutically.

The latest advances in the discovery of nitric oxide hybrid drug compounds

INTRODUCTION

There is a great interest in Nitric oxide (NO) within medicinal chemistry since it's involved in human signaling pathways. Prodrugs or hybrid compounds containing NO-donor scaffolds linked to an active compound are valuable, due to their potential for modulating many pathological conditions due to NO's biological properties when released in addition to the native drug. Compounds that selectively inhibit nitric oxide synthase isoforms (NOS) can also increase therapeutic capacity, particularly in the treatment of chronic diseases. However, search for bioactive compounds to efficiently and selectively modulate NO is still a challenge in drug discovery. Areas covered: In this review, the authors highlight the recent advances in the strategies used to discover NO-hybrid derivatives, especially those related to anti-inflammatory, cardiovascular, anticancer and anti-microorganism activities. They also focus on: nitric oxide synthase inhibitors, NO delivery materials and other related activities. Expert opinion: The process of molecular hybridization can be used to obtain NO-releasing compounds that also interact with different targets. The main problem with this approach is to control NO multiple actions in the right biological system. However, the use of NO-releasing groups with many different scaffolds leads to new molecular structures for bioactive compounds, suggesting synergies.

Discovery of phosphorodiamidate mustard-based O2-phosphorylated diazeniumdiolates with potent anticancer activity

Diazeniumdiolates are an important class of NO donors. Herein, we describe the design, synthesis and biological evaluation of a group of phosphorodiamidate mustard-based O²-phosphorylated diazeniumdiolates.

Recent advances in thromboresistant and antimicrobial polymers for biomedical applications: just say yes to nitric oxide (NO)

Biomedical devices are essential for patient diagnosis and treatment; however, when blood comes in contact with foreign surfaces or homeostasis is disrupted, complications including thrombus formation and bacterial infections can interrupt device functionality, causing false readings and/or shorten device lifetime. Here, we review some of the current approaches for developing antithrombotic and antibacterial materials for biomedical applications. Special emphasis is given to materials that release or generate low levels of nitric oxide (NO). Nitric oxide is an endogenous gas molecule that can inhibit platelet activation as well as bacterial proliferation and adhesion. Various NO delivery vehicles have been developed to improve NO's therapeutic potential. In this review, we provide a summary of the NO releasing and NO generating polymeric materials developed to date, with a focus on the chemistry of different NO donors, the polymer preparation processes, and in vitro and in vivo applications of the two most promising types of NO donors studied thus far, N-diazeniumdiolates (NONOates) and S-nitrosothiols (RSNOs).

Design, synthesis, and antitumor evaluation of novel histone deacetylase inhibitors equipped with a phenylsulfonylfuroxan module as a nitric oxide donor

On the basis of the strategy of creating multifunctional drugs, a novel series of phenylsulfonylfuroxan-based hydroxamates with histone deacetylase (HDAC) inhibitory and nitric oxide (NO) donating activities were designed, synthesized, and evaluated. The most potent NO donor-HDAC inhibitor (HDACI) hybrid, 5c, exhibited a much greater in vitro antiproliferative activity against the human erythroleukemia (HEL) cell line than that of the approved drug SAHA (Vorinostat), and its antiproliferative activity was diminished by the NO scavenger hemoglobin in a dose-dependent manner. Further mechanism studies revealed that 5c strongly induced cellular apoptosis and G1 phase arrest in HEL cells. Animal experiment identified 5c as an orally active agent with potent antitumor activity in a HEL cell xenograft model. Interestingly, although compound 5c was remarkably HDAC6-selective at the molecular level, it exhibited pan-HDAC inhibition in a western blot assay, which is likely due to class I HDACs inhibition caused by NO release at the cellular level.

Supplementation of bovine embryo culture medium with L-arginine improves embryo quality via nitric oxide production

Nitric oxide (NO) is a cell-signaling molecule that regulates a variety of molecular pathways. We investigated the role of NO during preimplantation embryonic development by blocking its production with an inhibitor or supplementing in vitro bovine embryo cultures with its natural precursor, L-arginine, over different periods. Endpoints evaluated included blastocyst rates, development kinetics, and embryo quality. Supplementation with the NO synthase inhibitor N-Nitro-L-arginine-methyl ester (L-NAME) from Days 1 to 8 of culture decreased blastocyst (P < 0.05) and hatching (P < 0.05) rates. When added from Days 1 to 8, 50 mM L-arginine decreased blastocyst rates (P < 0.001); in contrast, when added from Days 5 to 8, 1 mM L-arginine improved embryo hatching rates (P < 0.05) and quality (P < 0.05) as well as increased POU5F1 gene expression (P < 0.05) as compared to the untreated control. Moreover, NO levels in the medium during this culture period positively correlated with the increased embryo hatching rates and quality (P < 0.05). These data suggest exerts its positive effects during the transition from morula to blastocyst stage, and that supplementing the embryo culture medium with L-arginine favors preimplantation development of bovine embryos.

Gelatin-siloxane nanoparticles to deliver nitric oxide for vascular cell regulation: synthesis, cytocompatibility, and cellular responses

Nitric oxide (NO) is an important mediator in cardiovascular system to regulate vascular tone and maintain tissue homeostasis. Its role in vascular cell regulation makes it promising to address the post-surgery restenosis problem. However, the application of NO is constrained by its high reactivity. Here, we developed a novel NO-releasing gelatin-siloxane nanoparticle (GS-NO NP) to deliver NO effectively for vascular cell regulation. Results showed that gelatin-siloxane nanoparticles (GS NPs) could be synthesized via sol-gel chemistry with a diameter of ∼200 nm. It could be modified into GS-NO NPs via S-nitrosothiol (RSNO) modification. The synthesized GS-NO NPs could release a total of ∼0.12 µmol/mg NO sustainably for 7 days following a first-order exponential profile. They showed not only excellent cytocompatibility, but also rapid intracellularization within 2 h. GS-NO NPs showed inhibition of human aortic smooth muscle cell (AoSMC) proliferation and promotion of human umbilical vein endothelial cell (HUVEC) proliferation in a dose-dependent manner, which is an important approach to prevent restenosis. With GS-NO NP dose at 100 µg/mL, the proliferation of AoSMCs could be slowed down whereas the growth of HUVECs was significantly promoted. We concluded that GS-NO NPs could have potential to be used as a promising nano-system to deliver NO for vascular cell regulation.

Nitric oxide release: part II. Therapeutic applications

A wide range of nitric oxide (NO)-releasing materials has emerged as potential therapeutics that exploit NO's vast biological roles. Macromolecular NO-releasing scaffolds are particularly promising due to their ability to store and deliver larger NO payloads in a more controlled and effective manner compared to low molecular weight NO donors. While a variety of scaffolds (e.g., particles, dendrimers, and polymers/films) have been cleverly designed, the ultimate clinical utility of most NO-releasing macromolecules remains unrealized. Although not wholly predictive of clinical success, in vitro and in vivo investigations have enabled a preliminary evaluation of the therapeutic potential of such materials. In this tutorial review, we review the application of macromolecular NO therapies for cardiovascular disease, cancer, bacterial infections, and wound healing.

Sodium nitrite downregulates vascular NADPH oxidase and exerts antihypertensive effects in hypertension

Dietary nitrite and nitrate are important sources of nitric oxide (NO). However, the use of nitrite as an antihypertensive drug may be limited by increased oxidative stress associated with hypertension. We evaluated the antihypertensive effects of sodium nitrite given in drinking water for 4 weeks in two-kidney one-clip (2K1C) hypertensive rats and the effects induced by nitrite on NO bioavailability and oxidative stress. We found that, even under the increased oxidative stress conditions present in 2K1C hypertension, nitrite reduced systolic blood pressure in a dose-dependent manner. Whereas treatment with nitrite did not significantly change plasma nitrite concentrations in 2K1C rats, it increased plasma nitrate levels significantly. Surprisingly, nitrite treatment exerted antioxidant effects in both hypertensive and sham-normotensive control rats. A series of in vitro experiments was carried out to show that the antioxidant effects induced by nitrite do not involve direct antioxidant effects or xanthine oxidase activity inhibition. Conversely, nitrite decreased vascular NADPH oxidase activity. Taken together, our results show for the first time that nitrite has antihypertensive effects in 2K1C hypertensive rats, which may be due to its antioxidant properties resulting from vascular NADPH oxidase activity inhibition.

Modulating endothelial nitric oxide synthase: a new cardiovascular therapeutic strategy

The pathogenesis of many cardiovascular diseases is associated with reduced nitric oxide (NO) bioavailability and/or increased endothelial NO synthase (eNOS)-dependent superoxide formation. These findings support that restoring and conserving adequate NO signaling in the heart and blood vessels is a promising therapeutic intervention. In particular, modulating eNOS, e.g., through increasing the bioavailability of its substrate and cofactors, enhancing its transcription, and interfering with other modulators of eNOS pathway, such as netrin-1, has a high potential for effective treatments of cardiovascular diseases. This review provides an overview of the possibilities for modulating eNOS and how this may be translated to the clinic in addition to describing the genetic models used to study eNOS modulation.

The Nitric Oxide Prodrug V-PROLI/NO Inhibits Cellular Uptake of Proline

V-PYRRO/NO is a well studied nitric oxide (NO) prodrug which has been shown to protect human liver cells from arsenic, acetaminophen, and other toxic assaults in vivo. Its proline-based analogue, V-PROLI/NO, was designed to be a more biocompatible form that decomposes to the naturally occurring metabolites of proline, NO, and glycolaldehyde. Like V-PYRRO/NO, this cytochrome P450-activated prodrug was previously assumed to passively diffuse through the cellular membrane. Using (14)C-labeled proline in a competition assay, we show that V-PROLI/NO is transported through proline transporters into multiple cell lines. A fluorescent NO-sensitive dye (DAF-FM diacetate) and nitrite excretion indicated elevated intracellular NO release after metabolism over V-PYRRO/NO. These results also allowed us to predict and design a more permeable analogue, V-SARCO/NO. We report a proline transporter-based strategy for the selective transport of NO prodrugs that may have enhanced efficacy and aid in development of further NO prodrugs with increased permeability.

Apoptosis of hepatic stellate cells (HSC-T6) induced by sodium nitroprusside and mechanisms involved

AIM: To investigate whether nitric oxide (NO) donor sodium nitroprusside (SNP) can induce the apoptosis of hepatic stellate cells (HSC-T6) and to explore potential mechanisms involved.

METHODS: The apoptosis of HSC-T6 cells was determined by flow cytometry and Hoechst staining. The nuclear translocation of nuclear factor-κB (NF-κB) p65 was detected by laser scanning confocal microscopy. The expression of tissue inhibitor of matrix metalloproteinase-1 (TIMP-1), type I procollagen (procollagen I), and growth arrest and DNA damage-inducible protein (GADD45β) mRNAs was detected by real-time reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS: The apoptosis rate was significantly higher in HSC-T6 cells treated with SNP than in control cells (20.78% ± 5.91%vs 3.25% ± 1.26%, P = 0.031). Apoptotic HSC-T6 cells showed dense nuclear staining or granular fluorescence after Hoechst staining. Tumor necrosis factor-α (TNF-α)-mediated nuclear translocation of NF-κB p65 was inhibited by SNP treatment. With the increase in SNP dose, the expression levels of TIMP-1, procollagen I and GADD45β mRNAs were reduced (all P < 0.05).

CONCLUSION: SNP can induce the apoptosis of HSC-T6 cells and reduce the expression of TIMP-1 and procollagen I mRNAs perhaps by inhibiting NF-κB activity and reducing GADD45β mRNA expression.

Reduced ischemia/reperfusion injury via glutathione-initiated nitric oxide-releasing dendrimers

We report the therapeutic potential of S-nitroso-N-acetylpenicillamine-derivatized generation-4 polyamidoamine dendrimers (G4-SNAP) for reducing ischemia/reperfusion (I/R) injury in an isolated, perfused rat heart. The use of this dendrimer scaffold to deliver the nitrosothiol therapeutic did not inhibit NO donor activity as the required dose of G4-SNAP to minimize I/R injury (31nM corresponding to 2microM SNAP) was consistent with the optimum concentration of small molecule SNAP alone. An exploration of G4-SNAP NO release kinetics in the presence of physiologically relevant concentrations of glutathione (GSH) indicated enhanced NO release (t[NO]=1.28microM NO/mg) at 500microM GSH. Reperfusion experiments conducted with 500microM GSH further lowered the optimal therapeutic G4-SNAP dose to 230pM (i.e., 15nM SNAP). The unique combination of G4-SNAP dendrimer and glutathione trigger represents a novel strategy with possible clinical relevance toward salvaging ischemic tissue.

Aryl bis(diazeniumdiolates): potent inducers of S-glutathionylation of cellular proteins and their in vitro antiproliferative activities

A number of bis(diazeniumdiolates) that we designed to release up to 4 mol of nitric oxide (NO) and that are structural analogues of the NO prodrug and anticancer lead compound O(2)-{2,4-dinitro-5-[4-(N-methylamino)benzoyloxy]phenyl} 1-(N,N-dimethylamino)diazen-1-ium-1,2- diolate (PABA/NO) were synthesized and studied. A majority of these compounds yielded higher levels of NO, were better inhibitors of proliferation of a number of cancer cell lines, and more rapidly induced substantially increased levels of S-glutathionylation of cellular proteins in comparison with PABA/NO. In most cases, the antiproliferative activity and extents of S-glutathionylation correlated well with levels of intracellular NO release. We report bis(diazeniumdiolates) to be a class of S-glutathionylating agents with potent antiproliferative and S-glutathionylating activity.

Synthesis, mechanistic studies, and anti-proliferative activity of glutathione/glutathione S-transferase-activated nitric oxide prodrugs

Nitric oxide (NO) prodrugs such as O(2)-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K) are a growing class of promising NO-based therapeutics. Nitric oxide release from the anti-cancer lead compound, JS-K, is proposed to occur through a nucleophilic aromatic substitution by glutathione (GSH) catalyzed by glutathione S-transferase (GST) to form a diazeniumdiolate anion that spontaneously releases NO. In this study, a number of structural analogues of JS-K were synthesized and their chemical and biological properties were compared with those of JS-K. The homopiperazine analogue of JS-K showed anti-cancer activity that is comparable with that of JS-K but with a diminished reactivity towards both GSH and GSH/GST; both the aforementioned compounds displayed no cytotoxic activity towards normal renal epithelial cell line at concentrations where they significantly diminished the proliferation of a panel of renal cancer cell lines. These properties may prove advantageous in the further development of this class of nitric oxide prodrugs as cancer therapeutic agents.

Cell-permeable esters of diazeniumdiolate-based nitric oxide prodrugs

Although O(2)-(2,4-dinitrophenyl) derivatives of diazeniumdiolate-based nitric oxide (NO) prodrugs bearing a free carboxylic acid group were activated by glutathione to release NO, these compounds were poor sources of intracellular NO and showed diminished antiproliferative activity against human leukemia HL-60 cells. The carboxylic acid esters of these prodrugs, however, were found to be superior sources of intracellular NO and potent inhibitors of HL-60 cell proliferation.

Synthesis of S-[13N]nitrosoglutathione (13N-GSNO) as a new potential PET imaging agent

In the present paper, a fast and reproducible method for the synthesis of S-[(13)N]nitrosoglutathione is reported for the first time. The labeling strategy is based on the production of [(13)N]NO(3)(-) via the (16)O(p,alpha)(13)N nuclear reaction in water, as opposed to the standardized production of [(13)N]NH(4)(+) in 2mM aqueous ethanol. Following the reduction of [(13)N]NO(3)(-) to [(13)N]NO(2)(-), the reaction with glutathione in the presence of hydrochloric acid led to the desired radiotracer with a good radiochemical yield (24.2+/-2.0% end of synthesis, n=5) in a short production time (3min from the end of bombardment).

NO-donating NSAIDs and cancer: an overview with a note on whether NO is required for their action

Nitric oxide-donating nonsteroidal anti-inflammatory drugs (NO-NSAIDs) consist of a conventional NSAID to which an NO-releasing moiety is attached covalently, often via a spacer molecule. NO-NSAIDs represent an emerging class of compounds with chemopreventive properties against a variety of cancers, demonstrated in preclinical models including cell culture systems and animal tumor models; their potential efficacy in humans has not been assessed. Their mechanism of action appears complex and involves the generation of reactive oxygen species, suppression of microsatellite instability in mismatch repair-deficient cells, and modulation of several signaling cascades that culminate in inhibited cell renewal and enhanced apoptosis. NO, long appreciated to be able to protect from and also promote cancer, is released form NO-NSAIDs and constitutes their defining property. Existing data are consistent with the notion that NO may mediate their anticancer effect. In addition there is evidence that long-term administration of NO-donating compounds is not associated with increased incidence of colon cancer. Whether NO release is required for the anticancer effect of NO-NSAIDs has being questioned by recent data indicating that, at least in the case of NO-aspirin, the NO-releasing moiety may serve as a leaving group while the spacer actually being the moiety responsible for its pharmacological action. Regardless of mechanistic issues, these compounds promise to contribute to the control of cancer.

Synthesis, nitric oxide release, and anti-leukemic activity of glutathione-activated nitric oxide prodrugs: Structural analogues of PABA/NO, an anti-cancer lead compound

Diazeniumdiolate anions and their prodrug forms are reliable sources of nitric oxide (NO) that have generated interest as promising therapeutic agents. A number of structural analogues of O(2)-(2,4-dinitro-5-(4-(N-methylamino)benzoyloxy)phenyl) 1-(N,N-dimethylamino)diazen-1-ium-1,2-diolate (PABA/NO), an anti-cancer lead compound that is designed to release NO upon activation by glutathione, were prepared. The nitric oxide release patterns of these O(2)-(2,4-dinitrophenyl) diazeniumdiolates in the presence of glutathione were tested and it was found that in the absence of competing pathways, these compounds release nearly quantitative amounts of NO. The ability of PABA/NO and its structural analogues to inhibit human leukemia cell proliferation was determined and it was found that compounds releasing elevated amounts of NO displayed superior cytotoxic effects.

Adulterated effects of nitric oxide-generating donors

Impaired cutaneous nitric oxide (NO) production is associated with diminished antioxidative capacity in skin cells, hindered wound healing, unbalanced inflammatory reactions, and disturbed immunological responses. Use of topically applied NO donors might represent an auspicious new therapeutic approach in the field of dermatology. But what is the appropriate NO-generating compound or system? In this issue, Mowbray et al. describe a new chemical inert NO donor that per se produces little inflammation in the skin.

Synthesis and in vitro anti-leukemic activity of structural analogues of JS-K, an anti-cancer lead compound

Structural analogues of JS-K, an anti-cancer lead compound, were prepared and their in vitro anti-leukemic activity was determined. The rate of nitric oxide release from the corresponding diazeniumdiolate anions did not appear to affect the anti-leukemic activity of the prodrug forms. Two compounds with potent inhibitory activity and a potentially favorable toxicological profile were identified.

Sulfur mustard downregulates iNOS expression to inhibit wound healing in a human keratinocyte model

BACKGROUND

Increased nitric oxide (NO) synthesized by inducible NO synthase (iNOS) is involved in inflammatory and pathological conditions. iNOS also regulates several biomarkers that accelerate normal wound healing. Effects of exposure to sulfur mustard (SM) on the skin include formation of blisters and slow-healing injuries. Promoting re-epithelialization is a challenging issue in the treatment of the delayed healing of SM-induced skin injuries.

OBJECTIVES

To clarify the role(s) of iNOS in wound healing and the effect of SM on iNOS expression in an in vitro wound assay to eventually develop therapies for SM skin injuries.

METHODS

A wound was created by scratching normal human epidermal keratinocytes grown in vitro. iNOS expression was monitored by Western blotting, fluorescence microscopy, and real-time RT-PCR. Wound healing was analyzed using digitalized image analysis software.

RESULTS

The level of iNOS peaked 24-48h after wounding. SM exposure strongly reduced iNOS protein and mRNA levels. Fluorescence microscopy revealed that induction of iNOS expression by wounding and inhibition of iNOS expression by SM occurred not only in the cells at the wound edge but also in cells in the surrounding area, suggesting that wounding may induce and SM may inhibit release of cytokines that stimulate iNOS expression. iNOS-specific small interfering RNAs caused a marked decrease of iNOS expression irrespective of wounding. Gene silencing also completely inhibited wound healing.

CONCLUSION

These results suggest that preventing SM-induced inhibition of iNOS may be a prospective strategy to promote wound healing in SM-exposed skin.

Pharmacological interventions for peripheral artery disease

Peripheral arterial disease (PAD) encompasses the vascular diseases caused primarily by atherosclerosis and thromboembolic pathophysiological processes that alter the normal structure and function of the aorta, its visceral arterial branches and the arteries of the upper and lower extremities. PAD is associated with an increased risk for cardiovascular morbidity and mortality. The goals for pharmacological therapy in PAD should focus on reducing cardiovascular risk, improving walking distance and preventing critical limb ischaemia. Exercise training plays a key role in the therapeutic assessment, as well stopping smoking. Antiplatelet therapy (aspirin) should be given to every PAD patient if there are no contraindications. Neither their combination nor anticoagulant therapy has shown additional benefit in PAD patients. Several pharmacological agents have been developed to improve the functional state of the claudicant and to relieve the symptoms. Many studied drugs have shown either no, a small or a potential benefit. With future development of new drugs for PAD, there is an absolute need for very strict well-designed protocols in order to evaluate the claudication distance, the progression of the disease and the reduction in cardiovascular morbidity and mortality. New developments should focus on improvement of endothelial function, vascular repair and enhancement of collateral circulation.

V-PROLI/NO, a prodrug of the nitric oxide donor, PROLI/NO

The sensitivity to decomposition of the nitric oxide (NO) donor ion, 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (PROLI/NO), complicates direct electrophilic substitution to form useful prodrug derivatives. A modified general synthetic approach involving 1-[2-(hydroxymethyl)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate ion (structure A, above) was used to prepare several PROLI/NO prodrugs including the previously inaccessible O2-vinyl derivative, V-PROLI/NO. Metabolism of V-PROLI/NO by liver microsomes enriched in human cytochrome P450 isoforms was demonstrated.

The role of mitochondria in pharmacotoxicology: a reevaluation of an old, newly emerging topic

In addition to their well-known critical role in energy metabolism, mitochondria are now recognized as the location where various catabolic and anabolic processes, calcium fluxes, various oxygen-nitrogen reactive species, and other signal transduction pathways interact to maintain cell homeostasis and to mediate cellular responses to different stimuli. It is important to consider how pharmacological agents affect mitochondrial biochemistry, not only because of toxicological concerns but also because of potential therapeutic applications. Several potential targets could be envisaged at the mitochondrial level that may underlie the toxic effects of some drugs. Recently, antiviral nucleoside analogs have displayed mitochondrial toxicity through the inhibition of DNA polymerase-γ (pol-γ). Other drugs that target different components of mitochondrial channels can disrupt ion homeostasis or interfere with the mitochondrial permeability transition pore. Many known inhibitors of the mitochondrial electron transfer chain act by interfering with one or more of the respiratory chain complexes. Nonsteroidal anti-inflammatory drugs (NSAIDs), for example, may behave as oxidative phosphorylation uncouplers. The mitochondrial toxicity of other drugs seems to depend on free radical production, although the mechanisms have not yet been clarified. Meanwhile, drugs targeting mitochondria have been used to treat mitochondrial dysfunctions. Importantly, drugs that target the mitochondria of cancer cells have been developed recently; such drugs can trigger apoptosis or necrosis of the cancer cells. Thus the aim of this review is to highlight the role of mitochondria in pharmacotoxicology, and to describe whenever possible the main molecular mechanisms underlying unwanted and/or therapeutic effects.

Aspects of nitric oxide in health and disease: a focus on hypertension and cardiovascular disease

Nitric oxide (nitrogen monoxide) (NO) plays an important role in a wide range of physiologic processes. A major mediator of endothelial function, NO regulates vasodilatory and antithrombotic actions in the vasculature and plays a role in reproductive functions, bronchodilation, bone formation, memory, insulin sensitivity, and gastrointestinal relaxation. NO is formed from NO synthase. Impaired NO bioactivity is strongly associated with endothelial dysfunction and cardiovascular disease, but is also implicated in a broad range of other disorders, including pulmonary hypertension, insulin resistance, erectile dysfunction, and preeclampsia. Numerous therapies designed to target NO are being investigated and developed, including NO donors and stimulants. The recent African-American Heart Failure Trial (A-HeFT) showed that the NO donor isosorbide dinitrate, combined with the vasodilator hydralazine, significantly reduced morbidity and mortality in black patients with moderate-to-severe heart failure. Antihypertensive drugs, including angiotensin-converting enzyme inhibitors, calcium channel blockers, and third-generation beta-blockers, are NO stimulants that have demonstrated significant improvement of endothelial function and NO bioactivity. Other cardiovascular therapies that may improve NO bioactivity include statins, l-arginine, and nonpharmacologic approaches such as exercise and dietary changes.