Development of a fluorescent indicator for nitric oxide based on the fluorescein chromophore

Differential Nitric Oxide Responses in Primary Cultured Keratinocytes and Fibroblasts to Visible and Near-Infrared Light

NO is a crucial signaling molecule involved in skin health, the immune response, and the protection against environmental stressors. This study explores how different wavelengths of light, namely blue (455 nm), red (660 nm), and near infrared (NIR, 850 nm), affect nitric oxide (NO) production in skin cells. Primary keratinocytes and fibroblasts from three donors were exposed to these wavelengths, and NO production was quantified using a DAF-FM fluorescent probe. The results demonstrated that all three wavelengths stimulated NO release, with blue light showing the most pronounced effect. Specifically, blue light induced a 1.7-fold increase in NO in keratinocytes compared to red and NIR light and a 2.3-fold increase in fibroblasts compared to red light. Notably, fibroblasts exposed to NIR light produced 1.5 times more NO than those exposed to red light, while keratinocytes consistently responded more robustly across all wavelengths. In conclusion, blue light significantly boosts NO production in both keratinocytes and fibroblasts, making it the most effective wavelength. Red and NIR light, while less potent, also promote NO production and could serve as complementary therapeutic options, particularly for minimizing potential photoaging effects.

Ex Tenebris Lux: Illuminating Reactive Oxygen and Nitrogen Species with Small Molecule Probes

Reactive oxygen and nitrogen species are small reactive molecules derived from elements in the air─oxygen and nitrogen. They are produced in biological systems to mediate fundamental aspects of cellular signaling but must be very tightly balanced to prevent indiscriminate damage to biological molecules. Small molecule probes can transmute the specific nature of each reactive oxygen and nitrogen species into an observable luminescent signal (or even an acoustic wave) to offer sensitive and selective imaging in living cells and whole animals. This review focuses specifically on small molecule probes for superoxide, hydrogen peroxide, hypochlorite, nitric oxide, and peroxynitrite that provide a luminescent or photoacoustic signal. Important background information on general photophysical phenomena, common probe designs, mechanisms, and imaging modalities will be provided, and then, probes for each analyte will be thoroughly evaluated. A discussion of the successes of the field will be presented, followed by recommendations for improvement and a future outlook of emerging trends. Our objectives are to provide an informative, useful, and thorough field guide to small molecule probes for reactive oxygen and nitrogen species as well as important context to compare the ecosystem of chemistries and molecular scaffolds that has manifested within the field.

Determination of Nitric Oxide and Its Metabolites in Biological Tissues Using Ozone-Based Chemiluminescence Detection: A State-of-the-Art Review

Ozone-based chemiluminescence detection (CLD) has been widely applied for determining nitric oxide (•NO) and its derived species in many different fields, such as environmental monitoring and biomedical research. In humans and animals, CLD has been applied to determine exhaled •NO and •NO metabolites in plasma and tissues. The main advantages of CLD are high sensitivity and selectivity for quantitative analysis in a wide dynamic range. Combining CLD with analytical separation techniques like chromatography allows for the analytes to be quantified with less disturbance from matrix components or impurities. Sampling techniques like microdialysis and flow injection analysis may be coupled to CLD with the possibility of real-time monitoring of •NO. However, details and precautions in experimental practice need to be addressed and clarified to avoid wrong estimations. Therefore, using CLD as a detection tool requires a deep understanding of the sample preparation procedure and chemical reactions used for liberating •NO from its derived species. In this review, we discuss the advantages and pitfalls of CLD for determining •NO species, list the different applications and combinations with other analytical techniques, and provide general practical notes for sample preparation. These guidelines are designed to assist researchers in comprehending CLD data and in selecting the most appropriate method for measuring •NO species.

EGCG, a Green Tea Compound, Increases NO Production and Has Antioxidant Action in a Static and Shear Stress In Vitro Model of Preeclampsia

Preeclampsia (PE) is a gestational hypertensive disease characterized by endothelial dysfunction. Epigallocatechin-3-gallate (EGCG), the main compound in green tea, is a promising therapeutic target for the disease. By activating eNOS, EGCG increased NO production and exerted an important antioxidant action, but its specific impact in the context of PE remains understudied. The aim of this study is to evaluate the effects of EGCG on endothelial function in static and shear stress in in vitro models of PE. Endothelial cells were incubated with healthy (HP) and preeclamptic (PE) pregnant women's plasma, and the latter group was treated with EGCG. Additionally, NOS (L-NAME) and PI3K protein (LY249002) inhibitors were also used. The levels of NO, ROS, and O2•- were evaluated, as well as the antioxidant potential. These investigations were also carried out in a shear stress model. We found that EGCG increases the NO levels, which were reduced in the PE group. This effect was attenuated with the use of L-NAME and LY249002. Furthermore, EGCG increased the antioxidant capacity of PE, but its action decreased with LY294002. In cells subjected to shear stress, EGCG increased nitrite levels in the PE group and maintained its action on the antioxidant capacity. This is the first study of the effects of EGCG in this experimental model, as well as the investigation of its effects along with shear stress. Our findings suggest that EGCG improves parameters of endothelial dysfunction in vitro, making it a promising target in the search for treatments for the disease.

Reductases Produce Nitric Oxide in an Alternative Pathway to Form the Diazeniumdiolate Group of l-Alanosine

l-Alanosine is a diazeniumdiolate (N-nitrosohydroxylamine) antibiotic that inhibits MTAP-deficient tumor cells by blocking de novo adenine biosynthesis. Previous work revealed the early steps in the biosynthesis of l-alanosine. In the present study, we used genome mining to discover two new l-alanosine-producing strains that lack the aspartate-nitrosuccinate pathway genes found in the original l-alanosine producer. Instead, nitrate is reduced with a unique set of nitrate-nitrite reductases. These enzymes are typically used as part of the nitrogen cycle for denitrification or assimilation, and our report here shows how enzymes from the nitrogen cycle can be repurposed for the biosynthesis of specialized metabolites. The widespread distribution of nitric-oxide-producing reductases also indicates a potential for the discovery of new nitric-oxide-derived natural products.

Gold nanoparticle-based two-photon fluorescent nanoprobe for monitoring intracellular nitric oxide levels

Nitric oxide (NO) plays an important role in the regulation of the immune, cardiovascular and nervous systems. Consequently, being able to monitor and quantify intracellular NO levels would provide a greater understanding of the implications of this molecule in the different biological processes, including, for example, in cancer. Here, we report a broadly applicable two-photon excitable fluorescent nanoprobe able to detect and potentially quantify NO levels in an extensive range of cellular environments. The nanoprobe consists of a thiolated photoinduced electron transfer-based two=photon fluorescent probe attached onto the surface of 2.4 ± 0.7 nm gold nanoparticles (DANPY-NO@AuNPs). The nanoprobe, which can be synthesised in a reproducible manner and exhibits great stability when stored at room temperature, is able to selectively detect NO in solution, with a dynamic range up to 150 μM, and at pH values of biological relevance. DANPY-NO@AuNPs were able to selectively detect endogenous NO in RAW264.7γ NO^- macrophages and THP-1 human leukemic cells; and endogenous and exogenous NO in endothelial cells. The nanoprobe accumulated in the acidic organelles of the tested cell lines showing negligible toxicity. Importantly, DANPY-NO@AuNPs showed potential to quantify intracellular NO concentrations in MDA-MB-231 breast cancer cells. The biological evaluation of the nanoprobe was undertaken using confocal laser scanning (images and intracellular emission spectra) and multiphoton microscopies, and flow cytometry. Based on their excellent sensitivity and stability, and outstanding versatility, DANPY-NO@AuNPs can be applied for the spatiotemporal monitoring of in vitro and in vivo NO levels.

Methylarginine efflux in nutrient-deprived yeast mitigates disruption of nitric oxide synthesis

Protein arginine N-methyltransferases (PRMTs) have emerged as important actors in the eukaryotic stress response with implications in human disease, aging, and cell signaling. Intracellular free methylarginines contribute to cellular stress through their interaction with nitric oxide synthase (NOS). The arginine-dependent production of nitric oxide (NO), which is strongly inhibited by methylarginines, serves as a protective small molecule against oxidative stress in eukaryotic cells. NO signaling is highly conserved between higher and lower eukaryotes, although a canonical NOS homologue has yet to be identified in yeast. Since stress signaling pathways are well conserved among eukaryotes, yeast is an ideal model organism to study the implications of PRMTs and methylarginines during stress. We sought to explore the roles and fates of methylarginines in Saccharomyces cerevisiae. We starved methyltransferase-, autophagy-, and permease-related yeast knockouts by incubating them in water and monitored methylarginine production. We found that under starvation, methylarginines are expelled from yeast cells. We found that autophagy-deficient cells have an impaired ability to efflux methylarginines, which suggests that methylarginine-containing proteins are degraded via autophagy. For the first time, we determine that yeast take up methylarginines less readily than arginine, and we show that methylarginines impact yeast NO production. This study reveals that yeast circumvent a potential methylarginine toxicity by expelling them after autophagic degradation of arginine-modified proteins.

Gene Expression Changes Induced by Exposure of RAW 264.7 Macrophages to Particulate Matter of Air Pollution: The Role of Endotoxins

Despite the variable chemical and physical characteristics of particulate air pollutants, inflammation and oxidative stress have been identified as common mechanisms for cell damage and negative health influences. These effects are produced by organic components, especially by endotoxins. This study analyzed the gene expression profile after exposure of RAW 264.7 cells to the standard particulate matter (PM) material, NIST1648a, and PM with a reduced organic matter content, LAp120, in comparison to the effects of lipopolysaccharide (LPS). The selected parameters of cell viability, cell cycle progression, and metabolic and inflammatory activity were also investigated. Both forms of PM negatively influenced the parameters of cell activity. These results were generally reflected in the gene expression profile. Only NIST1648a, excluding LAp120, contained endotoxins and showed small but statistically significant pro-inflammatory activity. However, the gene expression profiling revealed strong pro-inflammatory cell activation induced by NIST1648a that was close to the effects of LPS. Changes in gene expression triggered by LAp120 were relatively small. The observed differences in the effects of NIST1648a and LAp120 were related to the content of organic matter in which bacterial endotoxins play an important role. However, other organic compounds and their interactions with other PM components also appear to be of significant importance.

Aedes aegypti sialokinin facilitates mosquito blood feeding and modulates host immunity and vascular biology

Saliva from mosquitoes contains vasodilators that antagonize vasoconstrictors produced at the bite site. Sialokinin is a vasodilator present in the saliva of Aedes aegypti. Here, we investigate its function and describe its mechanism of action during blood feeding. Sialokinin induces nitric oxide release similar to substance P. Sialokinin-KO mosquitoes produce lower blood perfusion than parental mosquitoes at the bite site during probing and have significantly longer probing times, which result in lower blood feeding success. In contrast, there is no difference in feeding between KO and parental mosquitoes when using artificial membrane feeders or mice that are treated with a substance P receptor antagonist, confirming that sialokinin interferes with host hemostasis via NK1R signaling. While sialokinin-KO saliva does not affect virus infection in vitro, it stimulates macrophages and inhibits leukocyte recruitment in vivo. This work highlights the biological functionality of salivary proteins in blood feeding.

Design, Synthesis, and Biological Evaluation of a Novel VEGFR-2 Inhibitor Based on a 1,2,5-Oxadiazole-2-Oxide Scaffold with MAPK Signaling Pathway Inhibition

Over the past few decades, the development of broad-spectrum anticancer agents with anti-angiogenic activity has witnessed considerable progress. In this study, a new series of pyrazolo[3,4-d]pyrimidines based on a phenylfuroxan scaffold were designed, synthesized, and evaluated, in terms of their anticancer activities. NCI-60 cell one-dose screening revealed that compounds 12a-c and 14a had the best MGI%, among the tested compounds. The target fluorinated compound 12b, as the most active one, showed better anticancer activity compared to the reference drug sorafenib, with IC50 values of 11.5, 11.6, and 13 µM against the HepG-2, A2780CP, and MDA-MB-231 cell lines, respectively. Furthermore, compound 12b (IC50 = 0.092 µM) had VEGFR-2-inhibitory activity comparable to that of the standard inhibitor sorafenib (IC50 = 0.049 µM). Furthermore, the ability of compound 12b in modulating MAPK signaling pathways was investigated. It was found to decrease the level of total ERK and its phosphorylated form, as well as leading to the down-regulation of metalloproteinase MMP-9 and the over-expression of p21 and p27, thus leading to subG1 cell-cycle arrest and, thus, the induction of apoptosis. Additionally, compound 12b decreased the rate of wound healing in the absence of serum, in comparison to DMSO-treated cells, providing a significant impact on metastasis inhibition. The quantitative RT-PCR results for E-cadherin and N-cadherin showed lower expression of the neuronal N-cadherin and increased expression of epithelial E-cadherin, indicating the ability of 12b to suppress metastasis. Furthermore, 12b-treated HepG2 cells expressed a low level of anti-apoptotic BCL-2 and over-expressed proapoptotic Bax genes, respectively. Using the DAF-FM DA fluorescence probe, compound 12b produced NO intracellularly as efficiently as the reference drug JS-K. In silico molecular docking studies showed a structural similarity through an overlay of 12b with sorafenib. Interestingly, the drug-likeness properties of compound 12b met the expectations of Pfizer's rule for the design of new drug candidates. Therefore, this study presents a novel anticancer lead compound that is worthy of further investigation and activity improvement.

Methods to Detect Nitric Oxide and Reactive Nitrogen Species in Biological Sample

Oxidative stress has been implicated in various human diseases, including cancer, mainly through the generation of reactive nitrogen species (RNS), such as nitric oxide (NO), nitrite, nitroxyl, s-nitrosothiols, and reactive oxygen species (ROS) such as peroxides, superoxide, and hydroxyl radicals. NO being the main player among RNS induced altered cellular molecules and metabolisms, thus making it important to understand and detect the generation of NO in biological samples. There are many methods for direct and indirect detection of NO; out of these most commonly used are spectrophotometric-based Griess assay and fluorescence probe-based assays. In this chapter, we summarize these routinely used methods to detect NO and various challenges associated with these methods.

A qnr-plasmid allows aminoglycosides to induce SOS in Escherichia coli

The plasmid-mediated quinolone resistance (PMQR) genes have been shown to promote high-level bacterial resistance to fluoroquinolone antibiotics, potentially leading to clinical treatment failures. In Escherichia coli, sub-minimum inhibitory concentrations (sub-MICs) of the widely used fluoroquinolones are known to induce the SOS response. Interestingly, the expression of several PMQR qnr genes is controlled by the SOS master regulator, LexA. During the characterization of a small qnrD-plasmid carried in E. coli, we observed that the aminoglycosides become able to induce the SOS response in this species, thus leading to the elevated transcription of qnrD. Our findings show that the induction of the SOS response is due to nitric oxide (NO) accumulation in the presence of sub-MIC of aminoglycosides. We demonstrated that the NO accumulation is driven by two plasmid genes, ORF3 and ORF4, whose products act at two levels. ORF3 encodes a putative flavin adenine dinucleotide (FAD)-binding oxidoreductase which helps NO synthesis, while ORF4 codes for a putative fumarate and nitrate reductase (FNR)-type transcription factor, related to an O₂-responsive regulator of hmp expression, able to repress the Hmp-mediated NO detoxification pathway of E. coli. Thus, this discovery, that other major classes of antibiotics may induce the SOS response could have worthwhile implications for antibiotic stewardship efforts in preventing the emergence of resistance.

Novel gene similar to nitrite reductase (NO forming) plays potentially important role in the latency of tuberculosis

The development of the latent phenotype of Mycobacterium tuberculosis (Mtb) in the human lungs is the major hurdle to eradicate Tuberculosis. We recently reported that exposure to nitrite (10 mM) for six days under in vitro aerobic conditions completely transforms the bacilli into a viable but non-cultivable phenotype. Herein, we show that nitrite (beyond 5 mM) treated Mtb produces nitric oxide (NO) within the cell in a dose-dependent manner. Our search for the conserved sequence of NO synthesizing enzyme in the bacterial system identified MRA2164 and MRA0854 genes, of which the former was found to be significantly up regulated after nitrite exposure. In addition, the purified recombinant MRA2164 protein shows significant nitrite dependent NO synthesizing activity. The knockdown of the MRA2164 gene at mRNA level expression resulted in a significantly reduced NO level compared to the wild type bacilli with a simultaneous return of its replicative capability. Therefore, this study first time reports that nitrite induces dormancy in Mtb cells through induced expression of the MRA2164 gene and productions of NO as a mechanism for maintaining non-replicative stage in Mtb. This observation could help to control the Tuberculosis disease, especially the latent phenotype of the bacilli.

Using diaminofluoresceins (DAFs) in nitric oxide research

Diaminofluoresceins (DAFs) are fluorescent probes widely applied to measure nitric oxide (NO) formation in cells and tissues. The main advantages of these compounds are their availability and low cost, and the general availability of instruments able to detect green fluorescence in all laboratories; these include fluorimeters, flow cytometers, and fluorescent microscopes. What made these molecules particularly interesting for many scientists approaching the NO field is that they are apparently very easy to use, as compared with other techniques requiring specific instrumentation and knowledge like chemiluminescence and electron paramagnetic resonance. However, the reactivity and biological chemistry of these probes in the cellular environment is rather complex and still not fully understood. Moreover, secondary reactions with ascorbate, or interference with thiols occur in cells. Therefore, the use of DAFs requires specific experimental planning and a careful interpretation of the results obtained. In this methodological review, we described in detail what is known about the reactivity of DAFs, their application in biological assays, list some principles to help experimental planning, including the necessary controls, and list the caveats concerning result interpretation. These guiding principles will help to understand the "Method behind our DAF-madness".

Sensing Nitric Oxide in Cells: Historical Technologies and Future Outlook

Nitric oxide (NO) is a critical cell signaling molecule with important roles in both normal cellular physiology and pathology. Over the past 20 years, multiple sensing modalities have been developed for the intracellular synthesis (endogenous) and release (exogenous) of NO. In this review, we survey the historical progression of NO sensing platforms, highlight the current state of the art, and offer a forward-looking view of how we expect the field of NO sensing to develop in the context of recent advances in bio-nanotechnology and nanoscale cellular biosensors.

The role of nitric oxide in ocular surface physiology and pathophysiology

Nitric oxide (NO) has a wide array of biological functions including the regulation of vascular tone, neurotransmission, immunomodulation, stimulation of proinflammatory cytokine expression and antimicrobial action. These functions may depend on the type of isoform that is responsible for the synthesis of NO. NO is found in various ocular tissues playing a pivotal role in physiological mechanisms, namely regulating vascular tone in the uvea, retinal blood circulation, aqueous humor dynamics, neurotransmission and phototransduction in retinal layers. Unregulated production of NO in ocular tissues may result in production of toxic superoxide free radicals that participate in ocular diseases such as endotoxin-induced uveitis, ischemic proliferative retinopathy and neurotoxicity of optic nerve head in glaucoma. However, the role of NO on the ocular surface in mediating physiology and pathophysiological processes is not fully understood. Moreover, methods used to measure levels of NO in the biological samples of the ocular surface are not well established due to its rapid oxidation. The purpose of this review is to highlight the role of NO in the physiology and pathophysiology of ocular surface and propose suitable techniques to measure NO levels in ocular surface tissues and tears. This will improve the understanding of NO's role in ocular surface biology and the development of new NO-based therapies to treat various ocular surface diseases. Further, this review summarizes the biochemistry underpinning NO's antimicrobial action.

Considerations of the importance of redox state for reactive nitrogen species action

Nitric oxide (NO) and other reactive nitrogen species (RNS) are immensely important signalling molecules in plants, being involved in a range of physiological responses. However, the exact way in which NO fits into signal transduction pathways is not always easy to understand. Here, some of the issues that should be considered are discussed. This includes how NO may interact directly with other reactive signals, such as reactive oxygen and sulfur species, how NO metabolism is almost certainly compartmentalized, that threshold levels of RNS may need to be reached to have effects, and how the intracellular redox environment may impact on NO signalling. Until better tools are available to understand how NO is generated in cells, where it accumulates, and to what levels it reaches, it will be hard to get a full understanding of NO signalling. The interaction of RNS metabolism with the intracellular redox environment needs further investigation. A changing redox poise will impact on whether RNS species can thrive in or around cells. Such mechanisms will determine whether specific RNS can indeed control the responses needed by a cell.

Design and synthesis of rosiglitazone-ferulic acid-nitric oxide donor trihybrids for improving glucose tolerance

Glucose intolerance is associated with metabolic syndrome and type 2 diabetes mellitus (T2DM) while some new therapeutic drugs, such as rosiglitazone (Rosi), for T2DM can cause severe cardiovascular side effects. Herein we report the synthesis of Rosi-ferulic acid (FA)-nitric oxide (NO) donor trihybrids to improve glucose tolerance and minimize the side effects. In comparison with Rosi, the most active compound 21 exhibited better effects on improving glucose tolerance, which was associated with its NO production, antioxidant and anti-inflammatory activities. Furthermore, 21 displayed relatively high stability in the simulated gastrointestinal environments and human liver microsomes, and released Rosi in plasma. More importantly, 21, unlike Rosi, had little stimulatory effect on the membrane translocation of aquaporin-2 (AQP2) in kidney collecting duct epithelial cells. These, together with a better safety profile, suggest that the trihybrids, like 21, may be promising candidates for intervention of glucose intolerance-related metabolic syndrome and T2DM.

Schiff bases containing a furoxan moiety as potential nitric oxide donors in plant tissues

Stable Schiff bases containing a furoxan moiety are synthesized as single regioisomers by the reaction of 3-methyl-2-oxy-furazan-4-carbaldehydewith various amino compounds at room temperature. The structures of synthesized compounds were fully characterized by multinuclear NMR spectroscopy and X-ray crystallography. The effect of synthesized Schiff bases containing a furoxan moiety on biological generation of reactive oxygen species and nitric oxide in plant tissues was investigated for the first time by fluorescence microscopy and the released NO identified as nitrite with Griess reagent. There is a good correlation between the biological generation of NO determined by fluorescence microscopy and with Griess reagent. Some of the synthesized compounds exhibited both nitric oxide and reactive oxygen species generation abilities and represent potential NO donors in plant tissues.

Nitric Oxide-Delivering High-Density Lipoprotein-like Nanoparticles as a Biomimetic Nanotherapy for Vascular Diseases

Disorders of blood vessels cause a range of severe health problems. As a powerful vasodilator and cellular second messenger, nitric oxide (NO) is known to have beneficial vascular functions. However, NO typically has a short half-life and is not specifically targeted. On the other hand, high-density lipoproteins (HDLs) are targeted natural nanoparticles (NPs) that transport cholesterol in the systemic circulation and whose protective effects in vascular homeostasis overlap with those of NO. Evolving the AuNP-templated HDL-like nanoparticles (HDL NPs), a platform of bioinspired HDL, we set up a targeted biomimetic nanotherapy for vascular disease that combines the functions of NO and HDL. A synthetic S-nitrosylated (SNO) phospholipid (1,2-dipalmitoyl-sn-glycero-3-phosphonitrosothioethanol) was synthesized and assembled with S-containing phospholipids and the principal protein of HDL, apolipoprotein A-I, to construct NO-delivering HDL-like particles (SNO HDL NPs). SNO HDL NPs self-assemble under mild conditions similar to natural processes, avoiding the complex postassembly modification needed for most synthetic NO-release nanoparticles. In vitro data demonstrate that the SNO HDL NPs merge the functional properties of NO and HDL into a targeted nanocarrier. Also, SNO HDL NPs were demonstrated to reduce ischemia/reperfusion injury in vivo in a mouse kidney transplant model and atherosclerotic plaque burden in a mouse model of atherosclerosis. Thus, the synthesis of SNO HDL NPs provides not only a bioinspired nanotherapy for vascular disease but also a foundation to construct diversified multifunctional platforms based on HDL NPs in the future.

Nitric oxide enhanced the growth of an obligated intracellular bacterium Orientia tsutsugamushi in murine macrophages

Orientia tsutsugamushi is the causative agent of scrub typhus. It is an obligate intracellular bacterium that grows only in eukaryotic cells. Macrophages play an important role in innate immunity by surveilling the human body for pathogens. In present study, it was demonstrated that O. tsutsugamushi propagated well in LPS-activated RAW 264.7 macrophages, but not in non-activated macrophages. In LPS-activated macrophages, the expression of Nos2, which encodes the inducible nitric oxide (NO) synthase (iNOS), was highly upregulated compared to those in non-activated macrophages. Parallel to this upregulation, high NO production was observed in LPS-activated macrophages. Transmissible electron microscopy showed that O. tsutsugamushi replicated in the cytosol of macrophages. Thus, O. tsutsugamushi was thought to escape the phagosomes at an early stage of phagosome maturation to avoid the bactericidal effect of NO. Furthermore, O. tsutsugamushi growth was enhanced in NO donor-supplied RAW 264.7 macrophages, as well as in LPS-activated, but not in non-activated macrophages. Consequently, these results suggested that NO was rather essential for enhancing the replication of O. tsutsugamushi in RAW 264.7 macrophages, despite the typically detrimental effects of NO against intracellular pathogens. In the present study, NO was suggested to activate specific pathways to enhance the growth of O. tsutsugamushi.

Isoxazole derivatives as new nitric oxide elicitors in plants

Several 3,5-disubstituted isoxazoles were obtained in good yields by regiospecific 1,3-dipolar cycloaddition reactions between aromatic nitrile oxides, generated in situ from the corresponding hydroxyimidoyl chlorides, with non-symmetrical activated alkynes in the presence of catalytic amounts of copper(I) iodide. Effects of 3,5-disubstituted isoxazoles on nitric oxide and reactive oxygen species generation in Arabidopsis tissues was studied using specific diaminofluoresceine dyes as fluorescence indicators.

Bioactive silicon nitride: A new therapeutic material for osteoarthropathy

While the reciprocity between bioceramics and living cells is complex, it is principally governed by the implant's surface chemistry. Consequently, a deeper understanding of the chemical interactions of bioceramics with living tissue could ultimately lead to new therapeutic strategies. However, the physical and chemical principles that govern these interactions remain unclear. The intricacies of this biological synergy are explored within this paper by examining the peculiar surface chemistry of a relatively new bioceramic, silicon nitride (Si3N4). Building upon prior research, this paper aims at obtaining new insights into the biological interactions between Si3N4 and living cells, as a consequence of the off-stoichiometric chemical nature of its surface at the nanometer scale. We show here yet unveiled details of surface chemistry and, based on these new data, formulate a model on how, ultimately, Si3N4 influences cellular signal transduction functions and differentiation mechanisms. In other words, we interpret its reciprocity with living cells in chemical terms. These new findings suggest that Si3N4 might provide unique new medicinal therapies and effective remedies for various bone or joint maladies and diseases.

Methods to Detect Nitric Oxide in Plants: Are DAFs Really Measuring NO?

Nitric oxide, a gaseous radical molecule, appears involved in many reactions in all living organisms. Fluorescent dyes like DAF-2 and related compounds are still widely used to monitor NO production inside or outside cells, although doubts about their specificity have recently been raised. We present evidence that DAF dyes do not only react with nitric oxide but also with peroxidase enzyme and hydrogen peroxide. Both are secreted in the case of elicitation of tobacco suspension cells with cryptogein, with a fluorescence increase mimicking NO release from cells. However, HPLC separation shows that fluorescence outside cells does not at all originate from DAF-2T, the product of DAF-2 and NO, but from other yet unidentified compounds. Inside cells, other DAF molecules are formed but only a minor part is DAF-2T. The chemical nature of the novel DAF derivatives still needs to be determined.

Preparation of a nitric oxide imaging agent from gelatin derivative micelles

INTRODUCTION

Nitric oxide (NO) is an intracellular and intercellular messenger that plays an important role in cellular events in physiological and pathophysiological processes. NO is one of the inflammation markers and macrophages of an inflammatory cell produce a large amount of NO compared with other cells. Non-invasive detection system of NO is highly required to realize an early therapeutic treatment considering the process of pathophysiological changes. The objective of this study is to develop an imaging agent of nitric oxide (NO).

METHODS

A water-insoluble DAR-4M of fluorescent dye for NO was solubilized in water through the micelle formation with gelatin grafted with l-α-phosphatidylethanolamine distearoyl (DAR-4M micelles). Physicochemical and biological properties of DAR-4M micelles were investigated by using cultured cells and animals.

RESULTS

The DAR-4M micelles responded to NO secreted from a NO donors, in contrast to the same concentration of free DAR-4M. When RAW264.7 of a macrophage cell line was stimulated by lipopolysaccharide (LPS) to allow them to generate NO, the DAR-4M micelles could detect NO of the cells to a significant great extent compared with free DAR-4M. After the intravenous injection of DAR-4M micelles or free DAR-4M to a mouse model of aristolochic acid (AA) induced acute interstitial nephritis, the DAR-4M micelles enhanced the fluorescence intensity from the kidneys to a significant great extent compared with the free DAR-4M injection. In case of DAR-4M micelles injection into normal mice, such an enhanced kidney fluorescence was not observed. A body distribution experiment demonstrated that the kidney accumulation of DAR-4M micelles was not modified by the AA-induced inflammation. After the AA injection, the number of CD11b-positive cells increased with time, indicating the increased number of inflammatory macrophages.

CONCLUSION

DAR-4M micelles are effective in imaging NO generated from macrophages accompanied with inflammation.

Photobiomodulation by Infrared Diode Laser: Effects on Intracellular Calcium Concentration and Nitric Oxide Production of Paramecium

In Paramecium, cilia beating is correlated to intracellular calcium concentration ([Ca²⁺ ]i) and nitric oxide (NO) synthesis. Recent findings affirm that photobiomodulation (PBM) can transiently increase the [Ca²⁺ ]i in mammalian cells. In this study, we investigated the effect of both 808 and 980 nm diode laser irradiated with flat-top hand-piece on [Ca²⁺ ]i and NO production of Paramecium primaurelia, to provide basic information for the development of new therapeutic approaches. In the experiments, the laser power in CW varied (0.1; 0.5; 1; and 1.5 W) to generate the following respective fluences: 6.4; 32; 64; and 96 J cm^-2 . The 6.4 J cm^-2 did not induce PBM if irradiated by both 808 and 980 nm diode laser. Conversely, the 32 J cm^-2 fluence had no effect on Paramecium cells if irradiated by the 808 nm laser, while if irradiated by the 980 nm laser induced increment in swimming speed (suggesting an effect on the [Ca²⁺ ]i, NO production, similar to the 64 J cm^-2 with the 808 nm wavelength). The more evident discordance occurred with the 96 J cm^-2 fluence, which had the more efficient effect on PBM among the parameters if irradiated with the 808 nm laser and killed the Paramecium cells if irradiated by the 980 nm laser. Lastly, the 980 nm and 64 or 96 J cm^-2 were the only parameters to induce a release of stored calcium.

Identification and functional analysis of endogenous nitric oxide in a filamentous fungus

In spite of its prevalence in animals and plants, endogenous nitric oxide (NO) has been rarely reported in fungi. We present here our observations on production of intracellular NO and its possible roles during development of Neurospora crassa, a model filamentous fungus. Intracellular NO was detected in hypha 8–16 hours after incubation in Vogel’s minimal liquid media and conidiophores during conidiation using a fluorescent indicator (DAF-FM diacetate). Treatment with cPTIO, an NO scavenger, significantly reduced fluorescence levels and hindered hyphal growth in liquid media and conidiation, whereas exogenous NO enhanced hyphal extension on VM agar media and conidia formation. NO scavenging also dramatically diminished transcription of con-10 and con-13, genes preferentially expressed during conidiation. Our results suggest that intracellular NO is generated in young hypha growing in submerged culture and during conidia development and regulate mycelial development and conidia formation.

Nitric oxide synthetic pathway and cGMP levels are altered in red blood cells from end-stage renal disease patients

Red blood cells (RBCs) enzymatically produce nitric oxide (NO) by a functional RBC-nitric oxide synthase (RBC-NOS). NO is a vascular key regulatory molecule. In RBCs its generation is complex and influenced by several factors, including insulin, acetylcholine, and calcium. NO availability is reduced in end-stage renal disease (ESRD) and associated with endothelial dysfunction. We previously demonstrated that, through increased phosphatidylserine membrane exposure, ESRD-RBCs augmented their adhesion to human cultured endothelium, in which NO bioavailability decreased. Since RBC-NOS-dependent NO production in ESRD is unknown, this study aimed to investigate RBC-NOS levels/activation, NO production/bioavailability in RBCs from healthy control subjects (C, N = 18) and ESRD patients (N = 27). Although RBC-NOS expression was lower in ESRD-RBCs, NO, cyclic guanosine monophosphate (cGMP), RBC-NOS Serine1177 phosphorylation level and eNOS/Calmodulin (CaM)/Heat Shock Protein-90 (HSP90) interaction levels were higher in ESRD-RBCs, indicating increased enzyme activation. Conversely, following RBCs stimulation with insulin or ionomycin, NO and cGMP levels were significantly lower in ESRD- than in C-RBCs, suggesting that uremia might reduce the RBC-NOS response to further stimuli. Additionally, the activity of multidrug-resistance-associated protein-4 (MRP4; cGMP-membrane transporter) was significantly lower in ESRD-RBCs, suggesting a possible compromised efflux of cGMP across the ESRD-RBCs membrane. This study for the first time showed highest basal RBC-NOS activation in ESRD-RBCs, possibly to reduce the negative impact of decreased NOS expression. It is further conceivable that high NO production only partially affects cell function of ESRD-RBCs maybe because in vivo they are unable to respond to physiologic stimuli, such as calcium and/or insulin.

Live-cell imaging approaches for the investigation of xenobiotic-induced oxidant stress

BACKGROUND

Oxidant stress is arguably a universal feature in toxicology. Research studies on the role of oxidant stress induced by xenobiotic exposures have typically relied on the identification of damaged biomolecules using a variety of conventional biochemical and molecular techniques. However, there is increasing evidence that low-level exposure to a variety of toxicants dysregulates cellular physiology by interfering with redox-dependent processes.

SCOPE OF REVIEW

The study of events involved in redox toxicology requires methodology capable of detecting transient modifications at relatively low signal strength. This article reviews the advantages of live-cell imaging for redox toxicology studies.

MAJOR CONCLUSIONS

Toxicological studies with xenobiotics of supra-physiological reactivity require careful consideration when using fluorogenic sensors in order to avoid potential artifacts and false negatives. Fortunately, experiments conducted for the purpose of validating the use of these sensors in toxicological applications often yield unexpected insights into the mechanisms through which xenobiotic exposure induces oxidant stress.

GENERAL SIGNIFICANCE

Live-cell imaging using a new generation of small molecule and genetically encoded fluorophores with excellent sensitivity and specificity affords unprecedented spatiotemporal resolution that is optimal for redox toxicology studies. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.

Traumatic Brain Injury Causes Endothelial Dysfunction in the Systemic Microcirculation through Arginase-1-Dependent Uncoupling of Endothelial Nitric Oxide Synthase

Endothelial dysfunction is a hallmark of many chronic diseases, including diabetes and long-term hypertension. We show that acute traumatic brain injury (TBI) leads to endothelial dysfunction in rat mesenteric arteries. Endothelial-dependent dilation was greatly diminished 24 h after TBI because of impaired nitric oxide (NO) production. The activity of arginase, which competes with endothelial NO synthase (eNOS) for the common substrate l-arginine, were also significantly increased in arteries, suggesting that arginase-mediated depletion of l-arginine underlies diminished NO production. Consistent with this, substrate restoration by exogenous application of l-arginine or inhibition of arginase recovered endothelial function. Moreover, evidence for increased reactive oxygen species production, a consequence of l-arginine starvation-dependent eNOS uncoupling, was detected in endothelium and plasma. Collectively, our findings demonstrate endothelial dysfunction in a remote vascular bed after TBI, manifesting as impaired endothelial-dependent vasodilation, with increased arginase activity, decreased generation of NO, and increased O₂^- production. We conclude that blood vessels have a "molecular memory" of neurotrauma, 24 h after injury, because of functional changes in vascular endothelial cells; these effects are pertinent to understanding the systemic inflammatory response that occurs after TBI even in the absence of polytrauma.

Elevated glucose and oligomeric β-amyloid disrupt synapses via a common pathway of aberrant protein S-nitrosylation

Metabolic syndrome (MetS) and Type 2 diabetes mellitus (T2DM) increase risk for Alzheimer's disease (AD). The molecular mechanism for this association remains poorly defined. Here we report in human and rodent tissues that elevated glucose, as found in MetS/T2DM, and oligomeric β-amyloid (Aβ) peptide, thought to be a key mediator of AD, coordinately increase neuronal Ca²⁺ and nitric oxide (NO) in an NMDA receptor-dependent manner. The increase in NO results in S-nitrosylation of insulin-degrading enzyme (IDE) and dynamin-related protein 1 (Drp1), thus inhibiting insulin and Aβ catabolism as well as hyperactivating mitochondrial fission machinery. Consequent elevation in Aβ levels and compromise in mitochondrial bioenergetics result in dysfunctional synaptic plasticity and synapse loss in cortical and hippocampal neurons. The NMDA receptor antagonist memantine attenuates these effects. Our studies show that redox-mediated posttranslational modification of brain proteins link Aβ and hyperglycaemia to cognitive dysfunction in MetS/T2DM and AD.

Alzheimer's disease is linked to metabolic syndrome and Type-2 diabetes, but the mechanism behind this association is unclear. Here, the authors show that elevated glucose and amyloid ß work together to increase nitrosative stress, leading to aberrant mitochondrial activity and synaptic dysfunction.

Nitric oxide and the cardiovascular system

Nitric oxide (NO) generated by endothelial cells to relax vascular smooth muscle is one of the most intensely studied molecules in the past 25 years. Much of what is known about NO regulation of NO is based on blockade of its generation and analysis of changes in vascular regulation. This approach has been useful to demonstrate the importance of NO in large scale forms of regulation but provides less information on the nuances of NO regulation. However, there is a growing body of studies on multiple types of in vivo measurement of NO in normal and pathological conditions. This discussion will focus on in vivo studies and how they are reshaping the understanding of NO's role in vascular resistance regulation and the pathologies of hypertension and diabetes mellitus. The role of microelectrode measurements in the measurement of [NO] will be considered because much of the controversy about what NO does and at what concentration depends upon the measurement methodology. For those studies where the technology has been tested and found to be well founded, the concept evolving is that the stresses imposed on the vasculature in the form of flow-mediated stimulation, chemicals within the tissue, and oxygen tension can cause rapid and large changes in the NO concentration to affect vascular regulation. All these functions are compromised in both animal and human forms of hypertension and diabetes mellitus due to altered regulation of endothelial cells and formation of oxidants that both damage endothelial cells and change the regulation of endothelial nitric oxide synthase.

Fluorescent Detection of Intracellular Nitric Oxide in Staphylococcus aureus

Nitric Oxide (NO) is a highly-reactive radical gas that can modify a variety of cellular targets in both eukaryotes and bacteria. NO is produced endogenously by a wide variety of organisms: For example, as a cell-signaling molecule in mammals and bacteria via nitric oxide synthase (NOS) enzymes, and as a product of denitrification. As such, it is of great benefit to NO researchers to be able to sensitively detect intracellular NO and stable reactive nitrogen species (RNS) derived from NO. To this end, a protocol for fluorescent detection of intracellular NO/RNS in biofilm cultures of the Gram-positive pathogen Staphylococcus aureus has been optimized using the commercially-available cell-permeable fluorescent stain 4-Amino-5-Methylamino-2', 7'-Difluorofluorescein Diacetate (DAF-FM diacetate). This compound diffuses into cells and intracellular cleavage by esterase enzymes liberates weakly-fluorescent DAF-FM, which reacts with NO or other specific RNS to become highly fluorescent (Kojima et al., 1999). Although quantification of fluorescence is performed using a fluorescent plate reader, it is envisioned that this protocol could be adapted for intracellular NO/RNS imaging of S. aureus biofilms by confocal microscopy. Likewise, this technique could be optimized for the detection of intracellular NO/RNS in other growth conditions (i.e., planktonic cultures) and/or in other bacteria/archaea.

Localization of Nitric Oxide in Wheat Roots by DAF Fluorescence

Nitric oxide is a free radical signal molecule. Various methods are available for measurement of NO. Out of all methods, fluorescent probes to localize NO is very widely used method. Diaminofluorescein in diacetate form (DAF-2DA) is most widely probe for NO measurement. This method is based on application of 4,5-diaminofluorescein diacetate (DAF-2DA) which is actively diffused into cells, once taken up by cells cytoplasmic esterases cleave the acetate groups to generate 4,5-diaminofluorescein; DAF-2. The generated DAF-2 can readily react with N2O3, which is an oxidation product of NO to generate the highly fluorescent DAF-2T (triazolofluorescein). There are various advantages and disadvantages associated with this method, but to its advantage in diffusion closely to NO producing sites, it is widely used for localization studies. Here, we describe method to make sections of the roots and localization of NO in roots subjected to hypoxic stress.

Nitric Oxide (NO) Measurements in Stomatal Guard Cells

The quantitative measurement of nitric oxide (NO) in plant cells acquired great importance, in view of the multifaceted function and involvement of NO as a signal in various plant processes. Monitoring of NO in guard cells is quite simple because of the large size of guard cells and ease of observing the detached epidermis under microscope. Stomatal guard cells therefore provide an excellent model system to study the components of signal transduction. The levels and functions of NO in relation to stomatal closure can be monitored, with the help of an inverted fluorescence or confocal microscope. We can measure the NO in guard cells by using flouroprobes like 4,5-diamino fluorescein diacetate (DAF-2DA). This fluorescent dye, DAF-2DA, is cell permeable and after entry into the cell, the diacetate group is removed by the cellular esterases. The resulting DAF-2 form is membrane impermeable and reacts with NO to generate the highly fluorescent triazole (DAF-2T), with excitation and emission wavelengths of 488 and 530 nm, respectively. If time-course measurements are needed, the epidermis can be adhered to a cover-glass or glass slide and left in a small petri dishes. Fluorescence can then be monitored at required time intervals; with a precaution that excitation is done minimally, only when a fluorescent image is acquired. The present method description is for the epidermis of Arabidopsis thaliana and Pisum sativum and should work with most of the other dicotyledonous plants.

A Novel Vasoactive Proline-Rich Oligopeptide from the Skin Secretion of the Frog Brachycephalus ephippium

Proline-rich oligopeptides (PROs) are a large family which comprises the bradykinin-potentiating peptides (BPPs). They inhibit the activity of the angiotensin I-converting enzyme (ACE) and have a typical pyroglutamyl (Pyr)/proline-rich structure at the N- and C-terminus, respectively. Furthermore, PROs decrease blood pressure in animals. In the present study, the isolation and biological characterization of a novel vasoactive BPP isolated from the skin secretion of the frog Brachycephalus ephippium is described. This new PRO, termed BPP-Brachy, has the primary structure WPPPKVSP and the amidated form termed BPP-BrachyNH₂ inhibits efficiently ACE in rat serum. In silico molecular modeling and docking studies suggest that BPP-BrachyNH₂ is capable of forming a hydrogen bond network as well as multiple van der Waals interactions with the rat ACE, which blocks the access of the substrate to the C-domain active site. Moreover, in rat thoracic aorta BPP-BrachyNH₂ induces potent endothelium-dependent vasodilatation with similar magnitude as captopril. In DAF-FM DA-loaded aortic cross sections examined by confocal microscopy, BPP-BrachyNH₂ was found to increase the release of nitric oxide (NO). Moreover, BPP-BrachyNH₂ was devoid of toxicity in endothelial and smooth muscle cell cultures. In conclusion, the peptide BPP-BrachyNH₂ has a novel sequence being the first BPP isolated from the skin secretion of the Brachycephalidae family. This opens for exploring amphibians as a source of new biomolecules. The BPP-BrachyNH₂ is devoid of cytotoxicity and elicits endothelium-dependent vasodilatation mediated by NO. These findings open for the possibility of potential application of these peptides in the treatment of endothelial dysfunction and cardiovascular diseases.

Traumatic brain injury disrupts cerebrovascular tone through endothelial inducible nitric oxide synthase expression and nitric oxide gain of function

BACKGROUND

Traumatic brain injury (TBI) has been reported to increase the concentration of nitric oxide (NO) in the brain and can lead to loss of cerebrovascular tone; however, the sources, amounts, and consequences of excess NO on the cerebral vasculature are unknown. Our objective was to elucidate the mechanism of decreased cerebral artery tone after TBI.

METHODS AND RESULTS

Cerebral arteries were isolated from rats 24 hours after moderate fluid‐percussion TBI. Pressure‐induced increases in vasoconstriction (myogenic tone) and smooth muscle Ca2+ were severely blunted in cerebral arteries after TBI. However, myogenic tone and smooth muscle Ca2+ were restored by inhibition of NO synthesis or endothelium removal, suggesting that TBI increased endothelial NO levels. Live native cell NO, indexed by 4,5‐diaminofluorescein (DAF‐2 DA) fluorescence, was increased in endothelium and smooth muscle of cerebral arteries after TBI. Clamped concentrations of 20 to 30 nmol/L NO were required to simulate the loss of myogenic tone and increased (DAF‐2T) fluorescence observed following TBI. In comparison, basal NO in control arteries was estimated as 0.4 nmol/L. Consistent with TBI causing enhanced NO‐mediated vasodilation, inhibitors of guanylyl cyclase, protein kinase G, and large‐conductance Ca2+‐activated potassium (BK) channel restored function of arteries from animals with TBI. Expression of the inducible isoform of NO synthase was upregulated in cerebral arteries isolated from animals with TBI, and the inducible isoform of NO synthase inhibitor 1400W restored myogenic responses following TBI.

CONCLUSIONS

The mechanism of profound cerebral artery vasodilation after TBI is a gain of function in vascular NO production by 60‐fold over controls, resulting from upregulation of the inducible isoform of NO synthase in the endothelium.

Nitric oxide synthesis by nitrate reductase is regulated during development in Aspergillus

Nitric oxide (NO) is a signalling molecule involved in many biological processes in bacteria, plants and mammals. However, little is known about the role and biosynthesis of NO in fungi. Here we show that NO production is increased at the early stages of the transition from vegetative growth to development in Aspergillus nidulans. Full NO production requires a functional nitrate reductase (NR) gene (niaD) that is upregulated upon induction of conidiation, even under N‐repressing conditions in the presence of ammonium. At this stage, NO homeostasis is achieved by balancing biosynthesis (NR) and catabolism (flavohaemoglobins). niaD and flavohaemoglobin fhbA are transiently upregulated upon induction of conidiation, and both regulators AreA and NirA are necessary for this transcriptional response. The second flavohaemoglobin gene fhbB shows a different expression profile being moderately expressed during the early stages of the transition phase from vegetative growth to conidiation, but it is strongly induced 24 h later. NO levels influence the balance between conidiation and sexual reproduction because artificial strong elevation of NO levels reduced conidiation and induced the formation of cleistothecia. The nitrate‐independent and nitrogen metabolite repression‐insensitive transcriptional upregulation of niaD during conidiation suggests a novel role for NR in linking metabolism and development.

Shear stress blunts tubuloglomerular feedback partially mediated by primary cilia and nitric oxide at the macula densa

The present study tested whether primary cilia on macula densa serve as a flow sensor to enhance nitric oxide synthase 1 (NOS1) activity and inhibit tubuloglomerular feedback (TGF). Isolated perfused macula densa was loaded with calcein red and 4,5-diaminofluorescein diacetate to monitor cell volume and nitric oxide (NO) generation. An increase in tubular flow rate from 0 to 40 nl/min enhanced NO production by 40.0 ± 1.2%. The flow-induced NO generation was blocked by an inhibitor of NOS1 but not by inhibition of the Na/K/2Cl cotransporter or the removal of electrolytes from the perfusate. NO generation increased from 174.8 ± 21 to 276.1 ± 24 units/min in cultured MMDD1 cells when shear stress was increased from 0.5 to 5.0 dynes/cm(2). The shear stress-induced NO generation was abolished in MMDD1 cells in which the cilia were disrupted using a siRNA to ift88. Increasing the NaCl concentration of the tubular perfusate from 10 to 80 mM NaCl in the isolated perfused juxtaglomerular preparation reduced the diameter of the afferent arteriole by 3.8 ± 0.1 μm. This response was significantly blunted to 2.5 ± 0.2 μm when dextran was added to the perfusate to increase the viscosity and shear stress. Inhibition of NOS1 blocked the effect of dextran on TGF response. In vitro, the effects of raising perfusate viscosity with dextran on tubular hydraulic pressure were minimized by reducing the outflow resistance to avoid stretching of tubular cells. These results suggest that shear stress stimulates primary cilia on the macula densa to enhance NO generation and inhibit TGF responsiveness.

Cooperative effects of matrix stiffness and fluid shear stress on endothelial cell behavior

Arterial hemodynamic shear stress and blood vessel stiffening both significantly influence the arterial endothelial cell (EC) phenotype and atherosclerosis progression, and both have been shown to signal through cell-matrix adhesions. However, the cooperative effects of fluid shear stress and matrix stiffness on ECs remain unknown. To investigate these cooperative effects, we cultured bovine aortic ECs on hydrogels matching the elasticity of the intima of compliant, young, or stiff, aging arteries. The cells were then exposed to laminar fluid shear stress of 12 dyn/cm(2). Cells grown on more compliant matrices displayed increased elongation and tighter EC-cell junctions. Notably, cells cultured on more compliant substrates also showed decreased RhoA activation under laminar shear stress. Additionally, endothelial nitric oxide synthase and extracellular signal-regulated kinase phosphorylation in response to fluid shear stress occurred more rapidly in ECs cultured on more compliant substrates, and nitric oxide production was enhanced. Together, our results demonstrate that a signaling cross talk between stiffness and fluid shear stress exists within the vascular microenvironment, and, importantly, matrices mimicking young and healthy blood vessels can promote and augment the atheroprotective signals induced by fluid shear stress. These data suggest that targeting intimal stiffening and/or the EC response to intima stiffening clinically may improve vascular health.

Dabigatran etexilate retards the initiation and progression of atherosclerotic lesions and inhibits the expression of oncostatin M in apolipoprotein E-deficient mice

Objective

Thrombin has multiple proatherogenic effects including platelet activation and the induction of inflammatory processes. Recently, the cytokine oncostatin M has been shown to have proinflammatory effects. This study was designed to investigate the effects of thrombin inhibition on the initiation and progression of atherosclerosis and on the expression of oncostatin M.

Methods

Apolipoprotein E-deficient mice at different ages were fed the thrombin inhibitor dabigatran etexilate. The mean lesion area was measured in the aortic sinus and in the innominate artery. CD45-positive cells within the aortic tissue were measured by flow cytometry. Oncostatin M expression was measured in the tissue sections by immunocytochemistry.

Results

Treatment with dabigatran etexilate resulted in a significant reduction of the mean area of atherosclerotic lesions in the aortic sinus in both the young mice (11,176±1,500 μm² (control) versus 3,822±836 μm² (dabigatran etexilate), P<0.05) and selectively in the older mice at 28 weeks (234,099±13,500 μm² (control) versus 175,226±16,132 μm² (dabigatran etexilate), P<0.05). There were also fewer CD45-positive cells within the aortas of the dabigatran-treated mice and enhanced NO production in endothelial cells pretreated with dabigatran. In addition, the expression of oncostatin M was reduced in the lesions of dabigatran etexilate-treated mice.

Conclusion

Inhibition of thrombin by dabigatran retards the development of early lesions and the progression of some established lesions in ApoE–/– mice. It improves endothelial function and retards macrophage accumulation within the vascular wall. Dabigatran also inhibits the expression of oncostatin M, and this suggests that oncostatin M may play a role in the initiation and progression of atherosclerosis.

A fluorogenic assay for methylglyoxal

MG (methylglyoxal) is a potent glycating agent and an endogenous reactive dicarbonyl metabolite formed in all live cells and organisms. It is an important precursor of AGEs (advanced glycation end-products) and is implicated in aging and disease. MG is assayed by derivatization by 1,2-diaminobenzene derivatives in cell extracts. Such assays are not applicable to high sample throughput, subcellular, live-cell and in vivo estimations. The use of fluorogenic probes designed for NO (nitric oxide) detection in biological samples and living cells has inadvertently provided probes for the detection of dicarbonyls such as MG. We describe the application of DAF-2 (4,5-diaminofluorescein) and DAR-1 (4,5-diaminorhodamine) for the detection of MG in cell-free systems and application for high-throughput assay of glyoxalase activity and assay of glucose degradation products in peritoneal dialysis fluids. DAF-2 and DAR-1, as for related BODIPY probes, do not have sufficient sensitivity to detect MG in live cells. Care will also be required to control for NO and dehydroascorbate co-detection and interference from peroxidase catalysing the degradation of probes to MG and glyoxal. Fluorogenic detection of MG, however, has great potential to facilitate the assay of MG and to advance towards that capability of imaging this product in live cells in vitro and small animals in vivo.

Cerebral nitric oxide represses choroid plexus NFκB-dependent gateway activity for leukocyte trafficking

Chronic neuroinflammation is evident in brain aging and neurodegenerative disorders and is often associated with excessive nitric oxide (NO) production within the central nervous system (CNS). Under such conditions, increased NO levels are observed at the choroid plexus (CP), an epithelial layer that forms the blood-cerebrospinal fluid barrier (BCSFB) and serves as a selective gateway for leukocyte entry to the CNS in homeostasis and following injury. Here, we hypothesized that elevated cerebral NO levels interfere with CP gateway activity. We found that induction of leukocyte trafficking determinants by the CP and sequential leukocyte entry to the CSF are dependent on the CP epithelial NFκB/p65 signaling pathway, which was inhibited upon exposure to NO. Examining the CP in 5XFAD transgenic mouse model of Alzheimer's disease (AD-Tg) revealed impaired ability to mount an NFκB/p65-dependent response. Systemic administration of an NO scavenger in AD-Tg mice alleviated NFκB/p65 suppression at the CP and augmented its gateway activity. Together, our findings identify cerebral NO as a negative regulator of CP gateway activity for immune cell trafficking to the CNS.

Measurement of nitric oxide in mast cells with the fluorescent indicator DAF-FM diacetate

The production of nitric oxide in mast cells has been difficult to measure due to the low amounts made by mast cells, as well as limitations in the specificity and sensitivity of the assays available. We present here a sensitive and specific 96-well plate-based method to directly measure NO using the cell-permeable fluorescent compound DAF-FM diacetate.