Nitric Oxide-releasing Compounds Research Articles

Repurposing nitric oxide donating drugs in cancer therapy through immune modulation

BackgroundNitric oxide-releasing drugs are used for cardiovascular diseases; however, their effects on the tumor immune microenvironment are less clear. Therefore, this study explored the impact of nitric oxide donors on tumor progression in immune-competent mice.MethodsThe effects of three different nitric oxide-releasing compounds (SNAP, SNP, and ISMN) on tumor growth were studied in tumor-bearing mouse models. Three mouse tumor models were used: B16F1 melanoma and LL2 lung carcinoma in C57BL/6 mice, CT26 colon cancer in BALB/c mice, and LL2 lung carcinoma in NOD/SCID mice. After nitric oxide treatment, splenic cytokines and lymphocytes were analyzed by cytokine array and flow cytometry, and tumor-infiltrating lymphocytes in the TME were analyzed using flow cytometry and single-cell RNA sequencing.ResultsLow doses of three exogenous nitric oxide donors inhibited tumor growth in two immunocompetent mouse models but not in NOD/SCID immunodeficient mice. Low-dose nitric oxide donors increase the levels of splenic cytokines IFN-γ and TNF-α but decrease the levels of cytokines IL-6 and IL-10, suggesting an alteration in Th2 cells. Nitric oxide donors increased the number of CD8+ T cells with activation gene signatures, as indicated by single-cell RNA sequencing. Flow cytometry analysis confirmed an increase in infiltrating CD8+ T cells and dendritic cells. The antitumor effect of nitric oxide donors was abolished by depletion of CD8+ T cells, indicating the requirement for CD8+ T cells. Tumor inhibition correlated with a decrease in a subtype of protumor macrophages and an increase in a subset of Arg1-positive macrophages expressing antitumor gene signatures. The increase in this subset of macrophages was confirmed by flow cytometry analysis. Finally, the combination of low-dose nitric oxide donor and cisplatin induced an additive cancer therapeutic effect in two immunocompetent animal models. The enhanced therapeutic effect was accompanied by an increase in the cells expressing the gene signature of NK cell.ConclusionsLow concentrations of exogenous nitric oxide donors inhibit tumor growth in vivo by regulating T cells and macrophages. CD8+ T cells are essential for antitumor effects. In addition, low-dose nitric oxide donors may be combined with chemotherapeutic drugs in cancer therapy in the future.

New Nitric Oxide-Releasing Compounds as Promising Anti-Bladder Cancer Drugs.

Bladder cancer is a worldwide problem and improved therapies are urgently needed. In the search for newer strong antitumor compounds, herein, we present the study of three nitric oxide-releasing compounds and evaluate them as possible therapies for this malignancy. Bladder cancer cell lines T24 and 253J were used to evaluate the antiproliferative, antimigratory, and genotoxic effects of compounds. Moreover, we determined the NF-κB pathway inhibition, and finally, the survivin downregulation exerted by our molecules. The results revealed that compounds 1 and 3 exerted a high antiproliferative activity against bladder cancer cells through DNA damage and survivin downregulation. In addition, compound 3 reduced bladder cancer cell migration. We found that nitric oxide donors are promising molecules for the development of a new therapeutic targeting the underlying mechanisms of tumorigenesis and progression of bladder cancer.

A Focused Library of NO‐Donor Compounds with Potent Antiproliferative Activity Based on Green Multicomponent Reactions

Cancer is the second leading cause of death worldwide. Herein, a strategy to quickly and efficiently identify novel lead compounds to develop anticancer agents, using green multicomponent reactions followed by antiproliferative activity and structure-activity relationship studies, is described. A second-generation focused library of nitric oxide-releasing compounds was prepared by microwave-assisted Passerini and Ugi reactions. Nearly all compounds displayed potent antiproliferative activities against a panel of human solid tumor cell lines, with 1-phenyl-1-[(tert-butylamino)carbonyl]methyl 3-[(3-phenylsulfonyl-[1,2,5]oxadiazol-4-yl N2 -oxide)oxy]benzoate (4 k) and N-[1-(tert-butylaminocarbonyl)-1-phenylmethyl]-N-(4-methylphenyl)-3-(3-phenylsulfonyl-[1,2,5]oxadiazol-4-yl N2 -oxide)oxyphenyl carboxamide (6 d) exhibiting the strongest activity on SW1573 lung cell line (GI50 =110 and 21 nm) with selectivity indices of 70 and 470, respectively. Preliminary mechanistic studies suggest a relationship between NO release and antiproliferative activity. Our strategy allowed the rapid identification of at least two molecules as future candidates for the development of potent antitumor drugs.

Anticancer efficacy of a nitric oxide-modified derivative of bifendate against multidrug-resistant cancer cells.

The development of multidrug resistance (MDR) not only actively transports a wide range of cytotoxic drugs across drug transporters but is also a complex interaction between a number of important cellular signalling pathways. Nitric oxide donors appear to be a new class of anticancer therapeutics for satisfying all the above conditions. Previously, we reported furoxan‐based nitric oxide‐releasing compounds that exhibited selective antitumour activity in vitro and in vivo. Herein, we demonstrate that bifendate (DDB)‐nitric oxide, a synthetic furoxan‐based nitric oxide‐releasing derivative of bifendate, effectively inhibits the both sensitive and MDR tumour cell viability at a comparatively low concentration. Interestingly, the potency of DDB‐nitric oxide is the independent of inhibition of the functions and expressions of three major ABC transporters. The mechanism of DDB‐nitric oxide appears to be in two modes of actions by inducing mitochondrial tyrosine nitration and apoptosis, as well as by down‐regulating HIF‐1α expression and protein kinase B (AKT), extracellular signal‐regulated kinases (ERK), nuclear factor κB (NF‐κB) activation in MDR cells. Moreover, the addition of a typical nitric oxide scavenger significantly attenuated all the effects of DDB‐nitric oxide, indicating that the cytotoxicity of DDB‐nitric oxide is as a result of higher levels of nitric oxide release in MDR cancer cells. Given that acquired MDR to nitric oxide donors is reportedly difficult to achieve and genetically unstable, compound like DDB‐nitric oxide may be a new type of therapeutic agent for the treatment of MDR tumours.

Antitumoral Activity Of Nitric Oxide-Releasing Compounds

Despite significant improvements in the conventional anti-ovarian cancer therapies, tumor cell resistance to various cytostatic drugs remains a relevant problem. Therefore, the new cancer treatment strategies are being developed. Among many agents that have been studied for their potential anti-cancer activity, the most promising are the nitric oxide (NO) donors-syntethic compounds that release NO in vivo and/or in vitro. We have evaluated the effect of NO donors on the SK-OV-3 and OVCAR-3 ovarian cancer cell lines. We assessed some of the cancer cells' specific features: the uncontrolled proliferation, over-activation of particular signaling proteins, high resistance to therapeutics and elevated expression and secretion of invasiveness/metastatic factors. Two members of NONOates family were used: SPER/NO and DETA/NO. Cancer cell lines were cultured with different concentrations of NO donors. The cytotoxic, pro-apoptotic activity of NO donors and their impact on the phosphorylation status of STAT-3 and AKT in cells were determined. The expression of VEGF-A, MMPs and TGF-β was also evaluated. NO donors inhibited ovarian cancer cells growth making them also more susceptible to the cisplatin cytotoxic activity. Moreover, both NO donors induced apoptosis of cells and decreased activity of signaling proteins (STAT3 and AKT). Similarly, SPER/NO and DETA/NO lowered the secretion of pro-metastatic factors, responsible for cancer cells invasiveness. The obtained results show that both NO donors demonstrated a wide range of action on both ovarian cancer cell lines. Therefore, they have a high potential of being a supporting compounds in the cancer therapies.

Simultaneous determination of sildenafil citrate and some nitric oxide releasing drugs in human plasma using UPLC MS/MS

ObjectiveThe inadvertent combination of sildenafil (SLD) and nitric oxide releasing compounds (NRC) may cause a life threatening hypotension and conversion of coital angina into an irreversible one. The aim of this study was to develop and validate a UPLC MS/MS method for the simultaneous quantitative analysis of SLD, nicorandil (NRD), and ARG in human plasma to determine the safety margins for drug combinations. Design and methodChromatographic elution was achieved in 4min using gradient elution and an injection volume of 10μL. Electro-spray positive ionization (ESI+ve) detection and multiple-reaction monitoring mode (MRM) were used for detection. ResultsThe method was found to be linear (10–900ng/mL for SLD and NRD while 1–30μg/mL for ARG), accurate and precise (99.35±1.58, 99.62±1.13, and 100.04±1.22% for SLD, NRD and ARG; respectively) and met all other validation requirements. ConclusionThe developed UPLC MS/MS method is suitable for fast, sensitive, accurate and simultaneous determinations of SLD, NRD, and ARG in plasma.

Pulmonary hypertension, nitric oxide and nitric oxide-releasing compounds

Nitric oxide (NO) is an important molecule in the mammalian cardiovascular system and the elucidation of its biological role has led to the awarding of a Nobel prize in medicine. There have been many significant discoveries in NO biology over the past two decades and translation of these developments from bench to bedside has allowed an explosion of therapies for pulmonary hypertension. This article provides an overview of the NO pathway in the pulmonary circulation in maintenance of normal vascular tone as well as its dysregulation in pulmonary hypertension, and a discussion of therapies based on inhaled NO or manipulation of its downstream signaling pathways. Several therapies such as phosphodiesterase inhibitors are already in use, and various experimental therapies are also discussed.

In Vitro Metabolism of (Nitrooxy)butyl Ester Nitric Oxide-Releasing Compounds: Comparison with Glyceryl Trinitrate

We investigated the in vitro metabolism of two (nitrooxy)butyl ester nitric oxide (NO) donor derivatives of flurbiprofen and ferulic acid, [1,1'-biphenyl]-4-acetic acid-2-fluoro-alpha-methyl-4-(nitrooxy)butyl ester (HCT 1026) and 3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid 4-(nitrooxy)butyl ester (NCX 2057), respectively, in rat blood plasma and liver subcellular fractions compared with (nitrooxy)butyl alcohol (NOBA) and glyceryl trinitrate (GTN). HCT 1026 and NCX 2057 undergo rapid ubiquitous carboxyl ester hydrolysis to their respective parent compounds and NOBA. The nitrate moiety of this latter is subsequently metabolized to inorganic nitrogen oxides (NOx), predominantly in liver cytosol by glutathione S-transferase (GST) and to a lesser extent in liver mitochondria. If, however, in liver cytosol, the carboxyl ester hydrolysis is prevented by an esterase inhibitor, the metabolism at the nitrate moiety level does not occur. In blood plasma, HCT 1026 and NCX 2057 are not metabolized to NOx, whereas a slow but sustained NO generation in deoxygenated whole blood as detected by electron paramagnetic resonance indicates the involvement of erythrocytes in the bioactivation of these compounds. Differently from NOBA, GTN is also metabolized in blood plasma and more quickly metabolized by different GST isoforms in liver cytosol. The cytosolic GST-mediated denitration of these organic nitrates in liver limits their interaction with other intracellular compartments to possible generation of NO and/or their subsequent availability and bioactivation in the systemic circulation and extrahepatic tissues. We show the possibility of modulating the activity of hepatic cytosolic enzymes involved in the metabolism of (nitrooxy)butyl ester compounds, thus increasing the therapeutic potential of this class of compounds.

Featured Molecules: Nitric Oxide-Releasing Compounds

Fully manipulable Chime versions of nitric oxide-releasing compounds, for the article Nitrogen-Based Diazeniumdiolates: Versatile Nitric Oxide-Releasing Compounds in Biomedical Research and Potential Clinical Applications

Nitrogen-Based Diazeniumdiolates: Versatile Nitric Oxide-Releasing Compounds for Biomedical Research and Potential Clinical Applications

Nitric oxide-generating ions of the nitrogen-diazeniumdiolate class with the general structure R1R2N-[N(O)NO]1 have been prepared by exposing primary, secondary, and polyamines to nitric oxide (NO). The resulting complexes regenerate bioactive NO at physiological pH with half-lives ranging from 2 seconds to 20 hours. An important goal in our research is to deliver NO to a specific organ or cell type where it is needed without affecting other NO-sensitive parts of the anatomy. By taking advantage of the remarkable chemical versatility of diazeniumdiolates, we have developed general strategies to prepare either tissue-selective NO donor drugs or materials containing NO delivery agents that can be physically placed near the target sites. Inhibition of blood coagulation, induction of penile erection, relief of pulmonary hypertension, and reversal of cerebral vasospasm are a few examples of their potential clinical applications.

Mutagenicity of nitric oxide-releasing compounds in Escherichia coli: effect of superoxide generation and evidence for two mutagenic mechanisms

The mutagenicity of three nitric oxide (NO) donors, 3-morpholinosydnonimine (SIN-1), a compound generating the precursors of peroxynitrite NO and superoxide, diethylamine/NO (DEA/NO) and spermine/NO (SPER/NO), both releasing authentic NO was analyzed using Escherichia coli tester strains IC203, carrying a deletion of the oxyR gene, and its oxyR + parent IC188 (the alternative name of WP2 uvrA/pKM101). The OxyR protein is a redox-sensitive transcriptional activator of genes encoding antioxidant enzymes. Strains IC203 and IC188 contain error-prone DNA polymerases polV, encoded by the chromosomal umuDC genes, and polRI, encoded by mucAB genes carried by pKM101. SIN-1 was determined to be an oxidative mutagen giving a positive response only in IC203, whereas DEA/NO and SPER/NO induced similar positive responses in IC203 and IC188 and were considered as non-oxidative mutagens. The spectrum of ochre suppressors in Trp + revertants induced by SIN-1 in IC203 was characterized by a higher number of TA→AT transversions and GC→AT transitions, and a lower number of GC→TA transversions, with respect to the untreated control. The mutagenicity of SIN-1 in IC203, probably induced by peroxynitrite through reactive derivatives, was enhanced in the presence of plumbagin (PLB), a superoxide generator. Superoxide generation by PLB, as well as formation of peroxynitrite in cells treated with SIN-1, evaluated by monitoring the oxidation, respectively, of dihydroethidium and dihydrorhodamine 123, were greater in IC203 than in IC188. Formation of peroxynitrite in IC203 treated with SIN-1 was stimulated by PLB. After treatment with DEA/NO and SPER/NO the number of revertants scored in IC188 was higher than in strains IC187, containing only polV, and IC204, deficient in both polV and polRI. For these compounds, induced suppressor revertants in IC187 and IC204 were almost exclusively GC→AT transitions, whereas in IC188 significant levels of GC→TA and TA→AT transversions were also induced. Mutagenesis by both DEA/NO and SPER/NO was partially inhibited in the presence of PLB. The results show the usefulness of the new tester strain IC203 to differentiate NO-promoted mutagenic mechanisms that involve or do not involve oxygen radicals.

Nitric oxide interacts with the cAMP pathway to modulate capacitation of human spermatozoa

This study aimed to demonstrate nitric oxide production by human spermatozoa and to characterize the interaction between nitric oxide and cAMP-related pathway in the control of human sperm capacitation and protein tyrosine phosphorylation. Spermatozoa were incubated in Tyrode’s medium with or without bovine serum albumin (BSA), and nitric oxide was measured with the spin trap sodium N-methyl-D-glucamine dithiocarbamate. Under noncapacitating conditions, spermatozoa produced low levels of nitric oxide. However, under capacitating conditions, prominent nitric oxide adduct signals were obtained and a time-dependent increase of nitric oxide production was observed. When spermatozoa were incubated in Tyrode+BSA medium with nitric oxide-releasing compounds, intracellular cAMP concentrations increased to levels higher than those of spermatozoa incubated in Tyrode+BSA alone. In contrast, incubation with nitric oxide synthase inhibitors (N G-nitro- l-arginine methyl ester or N G-monomethyl l-arginine) decreased intracellular sperm cAMP concentrations. The inhibitory effect observed with N G-nitro- l-arginine methyl ester on capacitation and tyrosine phosphorylation of two sperm proteins (105, 81 kDa) was overcome by the presence of cAMP analogs or of a phosphodiesterase inhibitor. These results indicate that nitric oxide is produced by capacitating human spermatozoa and that it may act as a cellular messenger by modulating the cAMP pathway involved in capacitation and protein tyrosine phosphorylation.

Inhibition by nitric oxide-releasing compounds of E-selectin expression in and neutrophil adhesion to human endothelial cells

The effects of two chemically unrelated nitric oxide (NO)-releasing compounds were studied on adhesion molecule expression in and neutrophil adhesion to human umbilical vein endothelial cells. Incubation of confluent monolayers of endothelial cells with increasing concentrations of lipopolysaccharide stimulated the adhesion of polymorphonuclear leukocytes to endothelial cells. Flow cytometric analysis showed that lipopolysaccharide treatment upregulated the expression of adhesion molecules E-selectin and intercellular adhesion molecule-1 (ICAM-1) in human umbilical vein endothelial cells. A novel NO-releasing compound GEA 3175 (1,2,3,4-oxatriazolium,-3-(3-chloro-2-methylphenyl)-5-[[(4-methylphenyl)sulfonyl]amino]-, hydroxide inner salt) inhibited lipopolysaccharide-induced adhesion being more potent than the earlier known NO donor S-nitroso- N-acetylpenicillamine. The increased E-selectin expression induced by lipopolysaccharide was significantly attenuated by the two NO donors tested whereas ICAM-1 expression remained unaltered. The present data show that NO donors inhibit E-selectin expression in and neutrophil adhesion to lipopolysaccharide-stimulated vascular endothelial cells. Thus, by inhibiting leukocyte adhesion NO donors may reduce leukocyte infiltration and leukocyte-mediated tissue injury in inflammation and ischemia–reperfusion injury.

Nitric oxide-releasing compounds inhibit neutrophil adhesion to endothelial cells

In the present work, we demonstrated that chemically different nitric oxide (NO)-releasing compounds inhibit tumor necrosis factor α (TNF-α)-induced polymorphonuclear leukocyte adhesion to endothelial cells in vitro. Two mesoionic oxatriazole derivatives GEA 3162 (1,2,3,4-oxatriazolium,5-amino-3(3,4-dichlorophenyl)-chloride) and GEA 3175 (1,2,3,4-oxatriazolium,-3-(3-chloro-2-methylphenyl)-5-[[(4-methylphenyl)sulfonyl]amino]-, hydroxide inner salt) were compared to the earlier-known NO donor SIN-1 (3-morpholino-sydnonimine). GEA 3162 (3–10 μM) and GEA 3175 (10–30 μM) inhibited human polymorphonuclear leukocyte adhesion to B 4 endothelial cells in a dose-dependent manner being more potent than SIN-1. In the present model, leukocytes rather than endothelial cells seemed to be the target of the effect of NO. Flow cytometric analysis showed that NO-releasing compounds did not alter TNF-α induced CD11/CD18 surface expression in polymorphonuclear leukocytes. The inhibitory action of NO-releasing compounds on adhesion paralleled with the increased synthesis of cGMP in polymorphonuclear leukocytes. Analogues of cGMP inhibited polymorphonuclear leukocyte adhesion indicating a role for cGMP in the action of NO donors. The results suggest that exogenous NO in the form of NO-releasing compounds inhibits polymorphonuclear leukocyte adhesion to endothelial cells, which may be implicated in the regulation of leukocyte migration and leukocyte-mediated tissue injury.

Nitric oxide regulates human sperm capacitation and protein-tyrosine phosphorylation in vitro.

The aim of the present study was to investigate whether the generation of nitric oxide by human spermatozoa is associated with human sperm capacitation and with the tyrosine phosphorylation of sperm proteins. Human spermatozoa were capacitated in the presence or absence of nitric oxide-releasing compounds or nitric oxide synthase inhibitors, and then the percentage of acrosome loss induced by human follicular fluid or by calcium ionophore was determined. The presence of the nitric oxide-releasing compounds primed spermatozoa to respond earlier to human follicular fluid whereas nitric oxide synthase inhibitors decreased the percentage of acrosome reaction. Moreover, nitric oxide modulated tyrosine phosphorylation of sperm proteins. A tight correlation between capacitation and tyrosine phosphorylation regulated by nitric oxide was observed. Results indicate that nitric oxide is involved in human sperm capacitation and emphasize the importance of oxidoreduction reactions in the fine control of sperm physiology.

Inhibition by nitric oxide-releasing compounds of prostacyclin production in human endothelial cells.

1. The effects of two chemically unrelated nitric oxide (NO)-releasing compounds were studied on prostacyclin production in lipopolysaccharide (LPS)-stimulated human umbilical vein endothelial cells (HUVECs). The cells expressed cyclooxygenase-2 (COX-2) protein and produced prostacyclin by NS-398-sensitive manner suggesting that prostacyclin production derives principally by COX-2 pathway. 2. A novel NO-releasing oxatriazole derivative GEA 3175 (1-30 microm) inhibited LPS-induced production of prostacyclin in HUVECs in a dose-dependent manner being more potent than the earlier known NO-donor S-nitroso-N-acetylpenicillamine (SNAP). 3. The effects of the two NO-donors on prostacyclin synthesis were reversed when red blood cells were added into the culture indicating that the effects are due to NO released from the compounds. 4. Addition of exogenous arachidonic acid into the culture did not alter the inhibitory action of NO-donors suggesting that phospholipases are not the target of action of NO. 5. The NO-donors did not inhibit prostacyclin production in the presence of a selective COX-2 inhibitor NS-398. These data suggest that NO affects COX-2 pathway rather than has an overall effect on cyclooxygenases. 6. NO-releasing compounds did not alter the level of COX-2 protein expression in LPS-treated HUVECs as measured by Western blot analysis. 7. The results suggest that NO-donors inhibit the activity of COX-2 in human endothelial cells. A link between NO and the regulation of eicosanoid synthesis could represent an important mechanism in controlling vascular and inflammatory responses in pathophysiological states and during treatment with nitrovasodilators.

Mechanisms of Ulcer Healing and Effects of Nonsteroidal Anti-inflammatory Drugs

Ulceration of the gastroduodenal mucosa occurs frequently in humans, particularly in patients with a history of peptic ulcer disease. In order for healing to occur, mucosal damage stimulates secretion of growth factors in the adjacent mucosa and ulcer bed. Peptic ulcer healing is accomplished by the filling of the mucosal defect with cells that migrate from the ulcer margin and by connective tissue, including microvessels originating from granulation tissue. Peptic ulcer healing is accelerated both in humans and experimental models by gastric acid inhibition, which enhances cell migration and maturation of the granulation tissue. In experimental models, peptic ulcer healing can also be accelerated by oral administration of basic fibroblast growth factor, which increases angiogenesis in the ulcer bed, or by nitric oxide-releasing compounds, which improve gastric blood flow. Clinical and experimental data indicate that traditional nonsteroidal anti-inflammatory drugs (NSAIDs) delay the healing of peptic ulcers by interfering with the action of growth factors, decreasing epithelial cell proliferation in the ulcer margin, decreasing angiogenesis in the ulcer bed, and slowing maturation of the granulation tissue. In order to reduce the gastroduodenal side-effects of NSAIDs, selective cyclo-oxygenase (COX)-2 inhibitors have been developed, which inhibit the inducible COX-2 isoform in inflammatory tissue but have only limited effect on the constitutive COX-1 isoform in the stomach. It has been reported that the selective COX-2 inhibitor L-745,337 has a reduced liability for gastrointestinal ulceration. In our chronic experimental gastric ulcer model in rats, however, delay of gastric ulcer healing with L-745,337 was comparable to that with ordinary NSAIDs. It has also been reported that nitric oxide-releasing NSAIDs have a low relative risk of gastrointestinal ulceration but, again, in our chronic gastric ulcer model, nitric oxide did not reverse NSAID-induced deleterious effects on ulcer healing. In contrast, the proton pump inhibitor omeprazole has been shown to reverse NSAID-induced deleterious effects on gastric ulcer healing in our model. Comparable results have also been reported in humans. Histologic analysis has shown that omeprazole reverses the effects of NSAIDs on cell proliferation, angiogenesis, and maturation of the granulation tissue. In conclusion, only highly effective gastric acid inhibition reliably reverses NSAID-induced delay of gastric ulcer healing.

Effects of nitric oxide-releasing compounds on the adhesion of melanocytes

Effects of nitric oxide-releasing compounds on the adhesion of melanocytes

Nitric oxide donor-mediated killing of bioluminescent Escherichia coli

The antimicrobial activities of two nitric oxide-releasing compounds against Escherichia coli were investigated by using recombinant E. coli cloned with a luciferase gene from Pyrophorus plagiophthalamus. Since luciferase uses intracellular ATP to generate visible light which can be measured from living cells in real time, we wanted to compare the extent to which cell viability parallels light emission. Results from luminescence measurements and CFU counts were in good agreement, and the decrease in light emission was shown to provide a rapid and more sensitive indication of cytotoxicity.

Nitric oxide-releasing compounds inhibit Dictyostelium discoideum aggregation without altering cGMP production

The effects of nitric oxide-releasing compounds on Dictyostelium discoideum cell development and guanylyl cyclase activity were studied. The addition of SNP (sodium nitroprusside) or SIN-1 (3-morpholino-syndnonimine) to starved cells inhibited their differentiation and aggregation in a concentration-dependent manner. In contrast to mammalian systems, SNP did not significantly affect guanylyl cyclase activity in cell lysates of D. discoideum nor did it stimulate cGMP production in intact cells. The results suggest that the inhibitory effects of NO on D. discoideum cell aggregation are through a mechanism independent of an effect on guanylyl cyclase activity.