Nitro-Oleic Acid Inhibits Stemness Maintenance and Enhances Neural Differentiation of Mouse Embryonic Stem Cells via STAT3 Signaling.

Nitro-oleic acid (NO2-OA), pluripotent cell-signaling mediator, was recently described as a modulator of the signal transducer and activator of transcription 3 (STAT3) activity. In our study, we discovered new aspects of NO2-OA involvement in the regulation of stem cell pluripotency and differentiation. Murine embryonic stem cells (mESC) or mESC-derived embryoid bodies (EBs) were exposed to NO2-OA or oleic acid (OA) for selected time periods. Our results showed that NO2-OA but not OA caused the loss of pluripotency of mESC cultivated in leukemia inhibitory factor (LIF) rich medium via the decrease of pluripotency markers (NANOG, sex-determining region Y-box 1 transcription factor (SOX2), and octamer-binding transcription factor 4 (OCT4)). The effects of NO2-OA on mESC correlated with reduced phosphorylation of STAT3. Subsequent differentiation led to an increase of the ectodermal marker orthodenticle homolog 2 (Otx2). Similarly, treatment of mESC-derived EBs by NO2-OA resulted in the up-regulation of both neural markers Nestin and ß-Tubulin class III (Tubb3). Interestingly, the expression of cardiac-specific genes and beating of EBs were significantly decreased. In conclusion, NO2-OA is able to modulate pluripotency of mESC via the regulation of STAT3 phosphorylation. Further, it attenuates cardiac differentiation on the one hand, and on the other hand, it directs mESC into neural fate.

Redox properties and human serum albumin binding of nitro-oleic acid.

Nitro-fatty acids modulate inflammatory and metabolic stress responses, thus displaying potential as new drug candidates. Herein, we evaluate the redox behavior of nitro-oleic acid (NO2-OA) and its ability to bind to the fatty acid transporter human serum albumin (HSA). The nitro group of NO2-OA underwent electrochemical reduction at -0.75 V at pH 7.4 in an aqueous milieu. Based on observations of the R-NO2 reduction process, the stability and reactivity of NO2-OA was measured in comparison to oleic acid (OA) as the negative control. These electrochemically-based results were reinforced by computational quantum mechanical modeling. DFT calculations indicated that both the C9-NO2 and C10-NO2 positional isomers of NO2-OA occurred in two conformers with different internal angles (69° and 110°) between the methyl- and carboxylate termini. Both NO2-OA positional isomers have LUMO energies of around -0.7 eV, affirming the electrophilic properties of fatty acid nitroalkenes. In addition, the binding of NO2-OA and OA with HSA revealed a molar ratio of ~7:1 [NO2-OA]:[HSA]. These binding experiments were performed using both an electrocatalytic approach and electron paramagnetic resonance (EPR) spectroscopy using 16-doxyl stearic acid. Using a Fe(DTCS)2 spin-trap, EPR studies also showed that the release of the nitro moiety of NO2-OA resulted in the formation of nitric oxide radical. Finally, the interaction of NO2-OA with HSA was monitored via Tyr and Trp residue electro-oxidation. The results indicate that not only non-covalent binding but also NO2-OA-HSA adduction mechanisms should be taken into consideration. This study of the redox properties of NO2-OA is applicable to the characterization of other electrophilic mediators of biological and pharmacological relevance.

Immunomodulatory effects of cyanobacterial toxin cylindrospermopsin on innate immune cells.

Cylindrospermopsin (CYN), a cyanobacterial toxin, is an important water pollutant with broad biological activity. It has been known mainly from tropical areas, but the area of occurrence of its producers is spreading to temperate climates. It can be found in high concentrations in the environment as well as in purified drinking waters. The aim of the study is to bring a basic information on the ability of CYN to interfere with mammalian innate immunity cells and thus increase the understanding of the immunomodulatory potency of CYN. This study investigated whether immune cells can be a target of CYN either alone or in combination with a model immunomodulatory agent, lipopolysaccharide (LPS). We examined the effects on cellular viability and inflammation signaling of CYN on murine macrophage-like RAW 264.7 cells. Macrophages were treated either with pure toxin (1 µM) or together with a known stimulator of immunologically active cells, bacterial or cyanobacterial LPS. CYN has had a significant effect on production on pro-inflammatory mediator tumor necrosis factor α (TNF-α) which correlates with its effect on reactive oxygen species (ROS) production. We found that CYN potentiated the effect of bacterial and cyanobacterial LPS that was documented by activation of inflammatory signaling pathways including mitogen-activated protein kinase p38 as well as consequent expression of inducible nitric oxide synthase (iNOS) and increased production of pro-inflammatory mediators such as nitric oxide (NO), TNF-α, interleukin-6 (IL-6). Our study brings one of the first information that contributes to the elucidation of immunomodulatory role of CYN in macrophages under normal and pro-inflammatory conditions.

Role of myeloid regulatory cells (MRCs) in maintaining tissue homeostasis and promoting tolerance in autoimmunity, inflammatory disease and transplantation.

Myeloid cells play a pivotal role in regulating innate and adaptive immune responses. In inflammation, autoimmunity, and after transplantation, myeloid cells have contrasting roles: on the one hand they initiate the immune response, promoting activation and expansion of effector T-cells, and on the other, they counter-regulate inflammation, maintain tissue homeostasis, and promote tolerance. The latter activities are mediated by several myeloid cells including polymorphonuclear neutrophils, macrophages, myeloid-derived suppressor cells, and dendritic cells. Since these cells have been associated with immune suppression and tolerance, they will be further referred to as myeloid regulatory cells (MRCs). In recent years, MRCs have emerged as a therapeutic target or have been regarded as a potential cellular therapeutic product for tolerance induction. However, several open questions must be addressed to enable the therapeutic application of MRCs including: how do they function at the site of inflammation, how to best target these cells to modulate their activities, and how to isolate or to generate pure populations for adoptive cell therapies. In this review, we will give an overview of the current knowledge on MRCs in inflammation, autoimmunity, and transplantation. We will discuss current strategies to target MRCs and to exploit their tolerogenic potential as a cell-based therapy.

Chromatin architecture changes and DNA replication fork collapse are critical features in cryopreserved cells that are differentially controlled by cryoprotectants.

In this work, we shed new light on the highly debated issue of chromatin fragmentation in cryopreserved cells. Moreover, for the first time, we describe replicating cell-specific DNA damage and higher-order chromatin alterations after freezing and thawing. We identified DNA structural changes associated with the freeze-thaw process and correlated them with the viability of frozen and thawed cells. We simultaneously evaluated DNA defects and the higher-order chromatin structure of frozen and thawed cells with and without cryoprotectant treatment. We found that in replicating (S phase) cells, DNA was preferentially damaged by replication fork collapse, potentially leading to DNA double strand breaks (DSBs), which represent an important source of both genome instability and defects in epigenome maintenance. This induction of DNA defects by the freeze-thaw process was not prevented by any cryoprotectant studied. Both in replicating and non-replicating cells, freezing and thawing altered the chromatin structure in a cryoprotectant-dependent manner. Interestingly, cells with condensed chromatin, which was strongly stimulated by dimethyl sulfoxide (DMSO) prior to freezing had the highest rate of survival after thawing. Our results will facilitate the design of compounds and procedures to decrease injury to cryopreserved cells.

Nitro-oleic acid regulates growth factor-induced differentiation of bone marrow-derived macrophages.

Many diseases accompanied by chronic inflammation are connected with dysregulated activation of macrophage subpopulations. Recently, we reported that nitro-fatty acids (NO2-FAs), products of metabolic and inflammatory reactions of nitric oxide and nitrite, modulate macrophage and other immune cell functions. Bone marrow cell suspensions were isolated from mice and supplemented with macrophage colony-stimulating factor (M-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF) in combination with NO2-OA for different times. RAW 264.7 macrophages were used for short-term (1-5min) experiments. We discovered that NO2-OA reduces cell numbers, cell colony formation, and proliferation of macrophages differentiated with colony-stimulating factors (CSFs), all in the absence of toxicity. In a case of GM-CSF-induced bone marrow-derived macrophages (BMMs), NO2-OA acts via downregulation of signal transducer and activator of transcription 5 and extracellular signal-regulated kinase (ERK) activation. In the case of M-CSF-induced BMMs, NO2-OA decreases activation of M-CSFR and activation of related PI3K and ERK. Additionally, NO2-OA also attenuates activation of BMMs. In aggregate, we demonstrate that NO2-OA regulates the process of macrophage differentiation and that NO2-FAs represent a promising therapeutic tool in the treatment of inflammatory pathologies linked with increased accumulation of macrophages in inflamed tissues.

Nitro-Oleic Acid Prevents Hypoxia- and Asymmetric Dimethylarginine-Induced Pulmonary Endothelial Dysfunction.

RATIONALE: Pulmonary hypertension (PH) represents a serious health complication accompanied with hypoxic conditions, elevated levels of asymmetric dimethylarginine (ADMA), and overall dysfunction of pulmonary vascular endothelium. Since the prevention strategies for treatment of PH remain largely unknown, our study aimed to explore the effect of nitro-oleic acid (OA-NO2), an exemplary nitro-fatty acid (NO2-FA), in human pulmonary artery endothelial cells (HPAEC) under the influence of hypoxia or ADMA. METHODS: HPAEC were treated with OA-NO2 in the absence or presence of hypoxia and ADMA. The production of nitric oxide (NO) and interleukin-6 (IL-6) was monitored using the Griess method and ELISA, respectively. The expression or activation of different proteins (signal transducer and activator of transcription 3, STAT3; hypoxia inducible factor 1α, HIF-1α; endothelial nitric oxide synthase, eNOS; intercellular adhesion molecule-1, ICAM-1) was assessed by the Western blot technique. RESULTS: We discovered that OA-NO2 prevents development of endothelial dysfunction induced by either hypoxia or ADMA. OA-NO2 preserves normal cellular functions in HPAEC by increasing NO production and eNOS expression. Additionally, OA-NO2 inhibits IL-6 production as well as ICAM-1 expression, elevated by hypoxia and ADMA. Importantly, the effect of OA-NO2 is accompanied by prevention of STAT3 activation and HIF-1α stabilization. CONCLUSION: In summary, OA-NO2 eliminates the manifestation of hypoxia- and ADMA-mediated endothelial dysfunction in HPAEC via the STAT3/HIF-1α cascade. Importantly, our study is bringing a new perspective on molecular mechanisms of NO2-FAs action in pulmonary endothelial dysfunction, which represents a causal link in progression of PH. Graphical Abstract ᅟ.

Nitro-oleic acid inhibits vascular endothelial inflammatory responses and the endothelial-mesenchymal transition.

BACKGROUND: Inflammatory-mediated pathological processes in the endothelium arise as a consequence of the dysregulation of vascular homeostasis. Of particular importance are mediators produced by stimulated monocytes/macrophages inducing activation of endothelial cells (ECs). This is manifested by excessive soluble pro-inflammatory mediator production and cell surface adhesion molecule expression. Nitro-fatty acids are endogenous products of metabolic and inflammatory reactions that display immuno-regulatory potential and may represent a novel therapeutic strategy to treat inflammatory diseases. The purpose of our study was to characterize the effects of nitro-oleic acid (OA-NO2) on inflammatory responses and the endothelial-mesenchymal transition (EndMT) in ECs that is a consequence of the altered healing phase of the immune response. METHODS: The effect of OA-NO2 on inflammatory responses and EndMT was determined in murine macrophages and murine and human ECs using Western blotting, ELISA, immunostaining, and functional assays. RESULTS: OA-NO2 limited the activation of macrophages and ECs by reducing pro-inflammatory cytokine production and adhesion molecule expression through its modulation of STAT, MAPK and NF-κB-regulated signaling. OA-NO2 also decreased transforming growth factor-ß-stimulated EndMT and pro-fibrotic phenotype of ECs. These effects are related to the downregulation of Smad2/3. CONCLUSIONS: The study shows the pleiotropic effect of OA-NO2 on regulating EC-macrophage interactions during the immune response and suggests a role for OA-NO2 in the regulation of vascular endothelial immune and fibrotic responses arising during chronic inflammation. GENERAL SIGNIFICANCE: These findings propose the OA-NO2 may be useful as a novel therapeutic agent for treatment of cardiovascular disorders associated with dysregulation of the endothelial immune response.

Nitrated fatty acids suppress angiotensin II-mediated fibrotic remodelling and atrial fibrillation.

AIM: Atrial fibrosis, one of the most striking features in the pathology of atrial fibrillation (AF), is promoted by local and systemic inflammation. Electrophilic fatty acid nitroalkenes, endogenously generated by both metabolic and inflammatory reactions, are anti-inflammatory mediators that in synthetic form may be useful as drug candidates. Herein we investigate whether an exemplary nitro-fatty acid can limit atrial fibrosis and AF. METHODS AND RESULTS: Wild-type C57BL6/J mice were treated for 2 weeks with angiotensin II (AngII) and vehicle or nitro-oleic acid (10-nitro-octadec-9-enoic acid, OA-NO2, 6 mg/kg body weight) via subcutaneous osmotic minipumps. OA-NO2 significantly inhibited atrial fibrosis and depressed vulnerability for AF during right atrial electrophysiological stimulation to levels observed for AngII-naive animals. Left atrial epicardial mapping studies demonstrated preservation of conduction homogeneity by OA-NO2. The protection from fibrotic remodelling was mediated by suppression of Smad2-dependent myofibroblast transdifferentiation and inhibition of Nox2-dependent atrial superoxide formation. CONCLUSION: OA-NO2 potently inhibits atrial fibrosis and subsequent AF. Nitro-fatty acids and possibly other lipid electrophiles thus emerge as potential therapeutic agents for AF, either by increasing endogenous levels through dietary modulation or by administration as synthetic drugs.

Nitro-oleic acid modulates classical and regulatory activation of macrophages and their involvement in pro-fibrotic responses.

Inflammation is an immune response triggered by microbial invasion and/or tissue injury. While acute inflammation is directed toward invading pathogens and injured cells, thus enabling tissue regeneration, chronic inflammation can lead to severe pathologies and tissue dysfunction. These processes are linked with macrophage polarization into specific inflammatory "M1-like" or regulatory "M2-like" subsets. Nitro-fatty acids (NO2-FAs), produced endogenously as byproducts of metabolism and oxidative inflammatory conditions, may be useful for treating diseases associated with dysregulated immune homeostasis. The goal of this study was to characterize the role of nitro-oleic acid (OA-NO2) in regulating the functional specialization of macrophages induced by bacterial lipopolysaccharide or interleukin-4, and to reveal specific signaling mechanisms which can account for OA-NO2-dependent modulation of inflammation and fibrotic responses. Our results show that OA-NO2 inhibits lipopolysaccharide-stimulated production of both pro-inflammatory and immunoregulatory cytokines (including transforming growth factor-ß) and inhibits nitric oxide and superoxide anion production. OA-NO2 also decreases interleukin-4-induced macrophage responses by inhibiting arginase-I expression and transforming growth factor-ß production. These effects are mediated via downregulation of signal transducers and activators of transcription, mitogen-activated protein kinase and nuclear factor-кB signaling responses. Finally, OA-NO2 inhibits fibrotic processes in an in vivo model of angiotensin II-induced myocardial fibrosis by attenuating expression of α-smooth muscle actin, systemic transforming growth factor-ß levels and infiltration of both "M1-" and "M2-like" macrophage subsets into afflicted tissue. Overall, the electrophilic fatty acid derivative OA-NO2 modulates a broad range of "M1-" and "M2-like" macrophage functions and represents a potential therapeutic approach to target diseases associated with dysregulated macrophage subsets.

Immunomodulatory Potency of Microcystin, an Important Water-Polluting Cyanobacterial Toxin.

Microcystins (MCs) are primarily hepatotoxins produced by cyanobacteria and are responsible for intoxication in humans and animals. There are many incidents of chronic exposure to MCs, which have been attributed to the inappropriate treatment of water supplies or contaminated food. Using RAW 264.7 macrophages, we showed the potency of microcystin-LR (MC-LR) to stimulate production of pro-inflammatory cytokines (tumor necrosis factor α and interleukin-6) as a consequence of fast nuclear factor κB and nitrogen-activated protein kinase activation. In contrast to other studies, the observed effects were not attributed to the intracellular inhibition of protein phosphatases 1/2A due to lack of specific transmembrane transporters for MCs. However, the MC-LR-induced activation of macrophages was effectively inhibited by a specific peptide that blocks signaling of receptors, which play a pivotal role in the innate immune responses. Taken together, we showed for the first time that MC-LR could interfere with macrophage receptors that are responsible for triggering the above-mentioned signaling pathways. These findings provide an interesting mechanistic explanation of some adverse health outcomes associated with toxic cyanobacteria and MCs.

Bone marrow-derived macrophages exclusively expressed caveolin-2: The role of inflammatory activators and hypoxia.

Caveolins are specific proteins involved in regulation of signal transduction to intracellular space. Still, their contribution to immune functions has not been completely clarified. Thus, we decided to characterize the expression of caveolins in bone marrow-derived macrophages (BMDMs) under resting and inflammatory conditions. The effect of classical activators (lipopolysaccharide, LPS; interferon-gamma, IFN-γ) was further potentiated with hypoxic (5% O2) conditions. The activation of p44/42-extracellular signal-regulated kinases 1 and 2 (ERK1/2) and expression of caveolin-1, -2, and -3, hypoxia inducible factor-1 alpha (HIF-1α), as well as inducible nitric oxide synthase (iNOS) was monitored using the Western blot technique. The production of nitric oxide (NO) and tumor necrosis factor-alpha (TNFα) was analyzed by Griess method or ELISA, respectively. BMDMs were also transfected with siRNA against caveolin-2. Importantly, our study showed for the first time that BMDMs expressed only caveolin-2, and its level decreased after activation of macrophages with LPS, IFN-γ, and/or hypoxia. The expression of caveolin-2 negatively correlates with the iNOS and HIF-1α protein levels, as well as with the LPS/IFN-γ- and hypoxia-induced activation of ERK1/2. We concluded that caveolin-2 is most probably involved in regulation of pro-inflammatory responses of BMDMs, triggered via activation of ERK1/2.

The crucial role of l-arginine in macrophage activation: What you need to know about it.

Nowadays, it is well recognized that amino acids are powerful molecules responsible for regulatory control over fundamental cellular processes. However, our understanding of the signaling cascades involved in amino acid sensing in organisms, as well as signal initiation, is largely limited. This is also the case of semi-essential amino acid l-arginine, which has multiple metabolic fates, and it is considered as one of the most versatile amino acids. Recently, some new and important facts have been published considering the role of l-arginine in the regulation of inflammatory processes in several human and mouse models, mediated also via the regulation of macrophage activation. Therefore, this mini review focuses on the actual summarization of information about (i) l-arginine bioavailability in organism, (ii) l-arginine-dependent regulation of nitric oxide synthase expression and nitric oxide production, and importantly (iii) its role in the activation of intracellular signaling pathways and G-protein-coupled receptors in macrophages.

Asymmetric dimethyl arginine induces pulmonary vascular dysfunction via activation of signal transducer and activator of transcription 3 and stabilization of hypoxia-inducible factor 1-alpha.

Pulmonary hypertension (PH), associated with imbalance in vasoactive mediators and massive remodeling of pulmonary vasculature, represents a serious health complication. Despite the progress in treatment, PH patients typically have poor prognoses with severely affected quality of life. Asymmetric dimethyl arginine (ADMA), endogenous inhibitor of endothelial nitric oxide synthase (eNOS), also represents one of the critical regulators of pulmonary vascular functions. The present study describes a novel mechanism of ADMA-induced dysfunction in human pulmonary endothelial and smooth muscle cells. The effect of ADMA was compared with well-established model of hypoxia-induced pulmonary vascular dysfunction. It was discovered for the first time that ADMA induced the activation of signal transducer and activator of transcription 3 (STAT3) and stabilization of hypoxia inducible factor 1α (HIF-1α) in both types of cells, associated with drastic alternations in normal cellular functions (e.g., nitric oxide production, cell proliferation/Ca(2+) concentration, production of pro-inflammatory mediators, and expression of eNOS, DDAH1, and ICAM-1). Additionally, ADMA significantly enhanced the hypoxia-mediated increase in the signaling cascades. In summary, increased ADMA may lead to manifestation of PH phenotype in human endothelial and smooth muscle cells via the STAT3/HIF-1α cascade. Therefore this signaling pathway represents the potential pathway for future clinical interventions in PH.

On the molecular pharmacology of resveratrol on oxidative burst inhibition in professional phagocytes.

Resveratrol-3,5,4'-trihydroxystilbene-possesses antioxidant activities in vitro. It dose-dependently inhibited the generation of peroxyl, hydroxyl, peroxides, and lipid peroxidation products in cell free systems. Oxidative burst of whole human blood stimulated with PMA, fMLP, OpZ, and A23187 was inhibited in a concentration-dependent way, indicating suppression of both receptor and nonreceptor activated chemiluminescence by resveratrol. Results from isolated human neutrophils revealed that resveratrol was active extracellularly as well as intracellularly in inhibiting the generation of reactive oxygen species. Liberation of ATP and analysis of apoptosis showed that in the concentration of 100 µM, resveratrol did not change the viability and integrity of isolated neutrophils. Western blot analysis documented that resveratrol in concentrations of 10 and 100 µM significantly decreased PMA-induced phosphorylation of PKC α/ß II. Dose-dependent inhibition of nitrite production and iNOS protein expression in RAW 264.7 cells indicated possible interference of resveratrol with reactive nitrogen radical generation in professional phagocytes. The results suggest that resveratrol represents an effective naturally occurring substance with potent pharmacological effect on oxidative burst of human neutrophils and nitric oxide production by macrophages. It should be further investigated for its pharmacological activity against oxidative stress in ischaemia reperfusion, inflammation, and other pathological conditions, particularly neoplasia.

Protective effects of 10-nitro-oleic acid in a hypoxia-induced murine model of pulmonary hypertension.

Pulmonary arterial hypertension (PAH) is characterized by adverse remodeling of pulmonary arteries. Although the origin of the disease and its underlying pathophysiology remain incompletely understood, inflammation has been identified as a central mediator of disease progression. Oxidative inflammatory conditions support the formation of electrophilic fatty acid nitroalkene derivatives, which exert potent anti-inflammatory effects. The current study investigated the role of 10-nitro-oleic acid (OA-NO2) in modulating the pathophysiology of PAH in mice. Mice were kept for 28 days under normoxic or hypoxic conditions, and OA-NO2 was infused subcutaneously. Right ventricular systolic pressure (RVPsys) was determined, and right ventricular and lung tissue was analyzed. The effect of OA-NO2 on cultured pulmonary artery smooth muscle cells (PASMCs) and macrophages was also investigated. Changes in RVPsys revealed increased pulmonary hypertension in mice on hypoxia, which was significantly decreased by OA-NO2 administration. Right ventricular hypertrophy and fibrosis were also attenuated by OA-NO2 treatment. The infiltration of macrophages and the generation of reactive oxygen species were elevated in lung tissue of mice on hypoxia and were diminished by OA-NO2 treatment. Moreover, OA-NO2 decreased superoxide production of activated macrophages and PASMCs in vitro. Vascular structural remodeling was also limited by OA-NO2. In support of these findings, proliferation and activation of extracellular signal-regulated kinases 1/2 in cultured PASMCs was less pronounced on application of OA-NO2.Our results show that the oleic acid nitroalkene derivative OA-NO2 attenuates hypoxia-induced pulmonary hypertension in mice. Thus, OA-NO2 represents a potential therapeutic agent for the treatment of PAH.

Asymmetric dimethylarginine regulates the lipopolysaccharide-induced nitric oxide production in macrophages by suppressing the activation of NF-kappaB and iNOS expression.

Two major effector systems are frequently implicated in the immune and endothelial cell alternations associated with inflammation. They include the enhanced production of reactive oxygen species and diminished bioavailability of nitric oxide (NO). Importantly, these processes can be regulated by endogenously produced methylarginines, inhibitors for NO derived from macrophages and endothelial cells. Therefore, the aim of this study was to show the potential pharmacological intervention of methylarginines (N(G)-methyl-L-arginine, L-NMMA; N(G), N(G)'-dimethyl-L-arginine-symmetric dimethylarginine, SDMA; and N(G), N(G)-dimethyl-L-arginine-asymmetric dimethylarginine, ADMA) in activation of murine peritoneal (RAW 264.7) and alveolar (MHS) macrophages with lipopolysaccharide from Gram-negative bacteria (LPS). The data presented in this study clearly declare that L-NMMA (1-50µM) and ADMA (10-50 µM) significantly inhibited the LPS-induced NO production from macrophages in a concentration-dependent manner. It was demonstrated, for the first time, that the ADMA- and L-NMMA-induced down regulation of NO production was accompanied by reduced expression of mRNA and protein for inducible NO synthase as well as decreased activation of nuclear factor-κB. Importantly, we found a negative correlation between the ADMA-dependent reduction of NO production and ADMA-increased superoxide formation, which indicates that ADMA can negatively affect the balance in LPS-induced macrophage-derived production of reactive mediators. The only effect of SDMA was observed for LPS-triggered superoxide production, which was significantly decreased in its highest concentration (50 µM). In summary, L-NMMA and ADMA can mediate their effects on macrophage activation via regulation of intracellular signaling pathways, which can affect critical functions in activated macrophages.

The unique role of dietary L-arginine in the acceleration of peritoneal macrophage sensitivity to bacterial endotoxin.

It is known that cells and organisms can indirectly "sense" changes in L-arginine availability via changes in the activity of various metabolic pathways. However, the mechanism(s) by which genes can be directly regulated by L-arginine in mammalian cells have not yet been elucidated. We investigated the effect of L-arginine in the in vivo model of peritoneal inflammation in mice and in vitro in RAW 264.7 macrophages. A detailed analysis of basic physiological functions and selected intracellular signaling cascades revealed that L-arginine is crucial for the acceleration of macrophage activation by bacterial lipopolysaccharide. L-arginine increased the production of reactive oxygen species, nitric oxide, release of Ca(2+), as well as inducible nitric oxide synthase expression. Interestingly, the effect of L-arginine on macrophage activation was dependent on the phosphorylation of mitogen-activated protein kinases and activity of phospholipase C. In RAW 264.7 cells, L-arginine was shown to modulate the response of macrophages toward lipopolysaccharide via the activation of G-protein-coupled receptors. According to our data, we concluded that L-arginine availability plays a key role in the initiation of intracellular signaling pathways that trigger the lipopolysaccharide-induced inflammatory responses in murine macrophages. Although macrophages are partially stimulated in the absence of extracellular L-arginine, the presence of this amino acid significantly accelerates the sensitivity of macrophages to bacterial endotoxin.

Myeloperoxidase deficiency preserves vasomotor function in humans.

AIMS: Observational studies have suggested a mechanistic link between the leucocyte-derived enzyme myeloperoxidase (MPO) and vasomotor function. Here, we tested whether MPO is systemically affecting vascular tone in humans. METHODS AND RESULTS: A total of 12 135 patients were screened for leucocyte peroxidase activity. We identified 15 individuals with low MPO expression and activity (MPO(low)), who were matched with 30 participants exhibiting normal MPO protein content and activity (control). Nicotine-dependent activation of leucocytes caused attenuation of endothelial nitric oxide (NO) bioavailability in the control group (P < 0.01), but not in MPO(low) individuals (P = 0.12); here the MPO burden of leucocytes correlated with the degree of vasomotor dysfunction (P = 0.008). To directly test the vasoactive properties of free circulating MPO, the enzyme was injected into the left atrium of anaesthetized, open-chest pigs. Myeloperoxidase plasma levels peaked within minutes and rapidly declined thereafter, reflecting vascular binding of MPO. Blood flow in the left anterior descending artery and the internal mammary artery (IMA) as well as myocardial perfusion decreased following MPO injection when compared with albumin-treated animals (P < 0.001). Isolated IMA-rings from animals subjected to MPO revealed markedly diminished relaxation in response to acetylcholine (P < 0.01) and nitroglycerine as opposed to controls (P < 0.001). CONCLUSION: Myeloperoxidase elicits profound effects on vascular tone of conductance and resistance vessels in vivo. These findings not only call for revisiting the biological functions of leucocytes as systemic and mobile effectors of vascular tone, but also identify MPO as a critical systemic regulator of vasomotion in humans and thus a potential therapeutic target.

Pathogenic cycle between the endogenous nitric oxide synthase inhibitor asymmetrical dimethylarginine and the leukocyte-derived hemoprotein myeloperoxidase.

BACKGROUND: The nitric oxide synthase inhibitor asymmetrical dimethylarginine (ADMA) and the leukocyte-derived hemoprotein myeloperoxidase (MPO) are associated with cardiovascular diseases. Activation of monocytes and polymorphonuclear neutrophils (PMNs) with concomitant release of MPO is regulated in a nitric oxide-dependent fashion. The aim of the study was to investigate a potential 2-way interaction between ADMA and MPO. METHODS AND RESULTS: Ex vivo, ADMA uptake by isolated human PMNs, the principal source of MPO in humans, significantly impaired nitric oxide synthase activity determined by gas chromatography-mass spectrometry. In humans, short-term ADMA infusion (0.0125 mg · kg(-1) · min(-1)) significantly increased MPO plasma concentrations. Functionally, PMN exposure to ADMA enhanced leukocyte adhesion to endothelial cells, augmented NADPH oxidase activity, and stimulated PMN degranulation, resulting in release of MPO. In vivo, a 28-day ADMA infusion (250 µmol · kg(-1) · d(-1)) in C57Bl/6 mice significantly increased plasma MPO concentrations, whereas this ADMA effect on MPO was attenuated by human dimethylarginine dimethylaminohydrolase1 (hDDAH1) overexpression. Moreover, the MPO-derived reactive molecule hypochlorous acid impaired recombinant hDDAH1 activity in vitro. In MPO(-/-) mice, the lipopolysaccharide-induced increase in systemic ADMA concentrations was abrogated. CONCLUSIONS: ADMA profoundly impairs nitric oxide synthesis of PMNs, resulting in increased PMN adhesion to endothelial cells, superoxide generation, and release of MPO. In addition, MPO impairs DDAH1 activity. Our data reveal an ADMA-induced cycle of PMN activation, enhanced MPO release, and subsequent impairment of DDAH1 activity. These findings not only highlight so far unrecognized cytokine-like properties of ADMA but also identify MPO as a regulatory switch for ADMA bioavailability under inflammatory conditions.