The Function of Nitric Oxide in the Immune System

Quantification of Nitric Oxide in Single Cells Using the Single-Probe Mass Spectrometry Technique

Nitric oxide (NO) is a small molecule that plays important roles in biological systems and human diseases. The abundance of intracellular NO is tightly related to numerous biological processes. Due to cell heterogeneity, the intracellular NO amounts significantly vary from cell to cell, and therefore, any meaningful studies need to be conducted at the single-cell level. However, measuring NO in single cells is very challenging, primarily due to the extremely small size of single cells and reactive nature of NO. In the current studies, the quantitative reaction between NO and amlodipine, a compound containing the Hantzsch ester group, was performed in live cells. The product dehydro amlodipine was then detected by the Single-probe single-cell mass spectrometry technique to quantify NO in single cells. The experimental results indicated heterogeneous distributions of intracellular NO amounts in single cells with the existence of subpopulations.

Nitric oxide mediated hypoxia dynamics in COVID-19

Several COVID-19 patients frequently experience with happy hypoxia. Sometimes, the level of nitric oxide (NO) in COVID-19 patients was found to be greater than in non-COVID-19 hypoxemics and most of the cases lower. Induced or inhaled NO has a long history of usage as a therapy for hypoxemia. Excessive production of ROS and oxidative stress lower the NO level and stimulates mitochondrial malfunction is the primary cause of hypoxia-mediated mortality in COVID-19. Higher level of NO in mitochondria also the cause of dysfunction, because, excess NO can also diffuse quickly into mitochondria or through mitochondrial nitric oxide synthase (NOS). A precise dose of NO may increase oxygenation while also acting as an effective inhibitor of cytokine storm. NOS inhibitors may be used in conjunction with iNO therapy to compensate for the patient's optimal NO level. NO play a key role in COVID-19 happy hypoxia and a crucial component in the COVID-19 pathogenesis that demands a reliable and easily accessible biomarker to monitor.

Red-Fleshed Apple Anthocyanin Extracts Attenuate Male Reproductive System Dysfunction Caused by Busulfan in Mice

In this research, we analyzed the effect of an intragastrical oral administration of red-fleshed apple anthocyanin extract (RAAE) on busulfan-treated mice. First, we showed that the most abundant component in RAAE was cyanidin 3-O-galactoside. To determine the effect of the RAAE, the mice were divided into control and four other different concentrations of RAAE feeding treatment groups (BA0, no RAAE; BA.1, 0.1 mg/kg; BA1, 1 mg/kg; and BA5, 5 mg/kg) following busulfan injection. We observed that RAAE treatments displayed ameliorative effects on male reproductive system dysfunction caused by busulfan, such as recovering the irregular arrangements of seminiferous tubules, increasing the number of spermatogonia and spermatocytes, improving sperm concentration by 3-fold in BA.1, and improving sperm motility by 2-fold in BA1. The liquid chromatography with tandem mass spectrometry (LC-MS/MS) analysis showed significant up- or downregulation of certain metabolites, such as lysophosphatidylcholine (LysoPC), L-arginine, glycine, anandamide, and L-carnitine, which could contribute to the positive effects of RAAE, especially in PBA1 (plasma of BA1) and PBA5 (plasma of BA5). Taken together, the results indicate that 1 mg/kg of RAAE is a suitable concentration for rescuing spermatogenesis in mice. The research suggests that RAAE could be a potential nutraceutical for protecting spermatogenesis after busulfan therapy in cancer.

Macrophages as host, effector and immunoregulatory cells in leishmaniasis: Impact of tissue micro-environment and metabolism

Leishmania are protozoan parasites that predominantly reside in myeloid cells within their mammalian hosts. Monocytes and macrophages play a central role in the pathogenesis of all forms of leishmaniasis, including cutaneous and visceral leishmaniasis. The present review will highlight the diverse roles of macrophages in leishmaniasis as initial replicative niche, antimicrobial effectors, immunoregulators and as safe hideaway for parasites persisting after clinical cure. These multiplex activities are either ascribed to defined subpopulations of macrophages (e.g., Ly6C^highCCR2⁺ inflammatory monocytes/monocyte-derived dendritic cells) or result from different activation statuses of tissue macrophages (e.g., macrophages carrying markers of of classical [M1] or alternative activation [M2]). The latter are shaped by immune- and stromal cell-derived cytokines (e.g., IFN-γ, IL-4, IL-10, TGF-β), micro milieu factors (e.g., hypoxia, tonicity, amino acid availability), host cell-derived enzymes, secretory products and metabolites (e.g., heme oxygenase-1, arginase 1, indoleamine 2,3-dioxygenase, NOS2/NO, NOX2/ROS, lipids) as well as by parasite products (e.g., leishmanolysin/gp63, lipophosphoglycan). Exciting avenues of current research address the transcriptional, epigenetic and translational reprogramming of macrophages in a Leishmania species- and tissue context-dependent manner.

Protective effects of dietary arginine against oxidative damage and hepatopancreas immune responses induced by T-2 toxin in Chinese mitten crab (Eriocheir sinensis)

T-2 toxin is a secondary metabolite produced by Fusarium spp. that is a major cereal and animal feed contaminant. T-2 toxin has numerous adverse effects on animals, including hepatotoxicity. Arginine (Arg) is closely associated with the regulation of immune responses and antioxidant activity in tissues. The objective of the present study was to evaluate the protective effects of dietary Arg against oxidative damage and immune responses of the hepatopancreas induced by T-2 toxin in Chinese mitten crab. According to the results, 3.17% Arg in the diet decreased alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase activity in the haemolymph significantly, when compared with the levels of activity in the T-2 toxin group. Arg supplementation also increased superoxide dismutase and glutathione peroxidase activity, while decreasing malondialdehyde concentrations in the hepatopancreas, when compared with the levels in the T-2 toxin group. In addition, 3.17% Arg in the diet increased acid phosphatase and alkaline phosphatase activity in the hepatopancreas, as well as albumin concentrations in the haemolymph, when compared with the T-2 toxin group. Dietary Arg also regulated the expression of antioxidant enzyme-related genes (mitochondrial manganese superoxide dismutase, cytosolic manganese superoxide dismutase, and catalase) and immune related genes (prophenoloxidase, NF-κB-like transcription factor Relish, and lipopolysaccharide-induced TNF-α factor) to alleviate the damage associated with the T-2 toxin. Furthermore, Arg ameliorated damage to the hepatopancreas microstructure in the crabs. The results of the present study indicate that dietary Arg could enhance the antioxidant and immune capacity of Chinese mitten crab against oxidative damage and immune injury to the hepatopancreas induced by T-2 toxin.

Myristoylation: An Important Protein Modification in the Immune Response

Protein N-myristoylation is a cotranslational lipidic modification specific to the alpha-amino group of an N-terminal glycine residue of many eukaryotic and viral proteins. The ubiquitous eukaryotic enzyme, N-myristoyltransferase, catalyzes the myristoylation process. Precisely, attachment of a myristoyl group increases specific protein–protein interactions leading to subcellular localization of myristoylated proteins with its signaling partners. The birth of the field of myristoylation, a little over three decades ago, has led to the understanding of the significance of protein myristoylation in regulating cellular signaling pathways in several biological processes especially in carcinogenesis and more recently immune function. This review discusses myristoylation as a prerequisite step in initiating many immune cell signaling cascades. In particular, we discuss the hitherto unappreciated implication of myristoylation during myelopoiesis, innate immune response, lymphopoiesis for T cells, and the formation of the immunological synapse. Furthermore, we discuss the role of myristoylation in inducing the virological synapse during human immunodeficiency virus infection as well as its clinical implication. This review aims to summarize existing knowledge in the field and to highlight gaps in our understanding of the role of myristoylation in immune function so as to further investigate into the dynamics of myristoylation-dependent immune regulation.

Melittin induces in vitro death of Leishmania (Leishmania) infantum by triggering the cellular innate immune response

BACKGROUND

Apis mellifera venom, which has already been recommended as an alternative anti-inflammatory treatment, may be also considered an important source of candidate molecules for biotechnological and biomedical uses, such as the treatment of parasitic diseases.

METHODS

Africanized honeybee venom from Apis mellifera was fractionated by RP-C18-HPLC and the obtained melittin was incubated with promastigotes and intracellular amastigotes of Leishmania (L.) infantum. Cytotoxicity to mice peritoneal macrophages was evaluated through mitochondrial oxidative activity. The production of anti- and pro-inflammatory cytokines, NO and H2O2 by macrophages was determined.

RESULTS

Promastigotes and intracellular amastigotes were susceptible to melittin (IC50 28.3 μg.mL(-1) and 1.4 μg.mL(-1), respectively), but also showed mammalian cell cytotoxicity with an IC50 value of 5.7 μg.mL(-1). Uninfected macrophages treated with melittin increased the production of IL-10, TNF-α, NO and H2O2. Infected melittin-treated macrophages increased IL-12 production, but decreased the levels of IL-10, TNF-α, NO and H2O2.

CONCLUSIONS

The results showed that melittin acts in vitro against promastigotes and intracellular amastigotes of Leishmania (L.) infantum. Furthermore, they can act indirectly on intracellular amastigotes through a macrophage immunomodulatory effect.

Nitric oxide synthase in innate and adaptive immunity: an update

Thirty years after the discovery of its production by activated macrophages, our appreciation of the diverse roles of nitric oxide (NO) continues to grow. Recent findings have not only expanded our understanding of the mechanisms controlling the expression of NO synthases (NOS) in innate and adaptive immune cells, but have also revealed new functions and modes of action of NO in the control and escape of infectious pathogens, in T and B cell differentiation, and in tumor defense. I discuss these findings, in the context of a comprehensive overview of the various sources and multiple reaction partners of NO, and of the regulation of NOS2 by micromilieu factors, antisense RNAs, and 'unexpected' cytokines.

The immunomodulation of inducible nitric oxide in scallop Chlamys farreri

Nitric oxide (NO) is an important signalling molecule which plays an indispensable role in immunity of all vertebrates and invertebrates. In the present study, the immunomodulation of inducible NO in scallop Chlamys farreri was examined by monitoring the alterations of haemocyte behaviours and related immune molecules in response to the stimulations of LPS and/or with S-Methylisothiourea Sulphate (SMT), an inhibitor of inducible NO synthase (NOS). The total activity of NOS and NO concentration in the haemolymph of scallop C. farreri increased significantly at 3, 6 and 12 h after LPS stimulation respectively, whereas their increases were fully repressed when scallops were treated in the collaborating of LPS and SMT. Meanwhile, some cellular and humoral immune parameters were determined after the stimulation of LPS and SMT to investigate the role of inducible NO in innate immunity of scallop. After LPS stimulation, the highest levels of haemocytes apoptosis and phagocytosis were observed at 24 h (38.5 ± 2.5%, P < 0.01) and 12 h (38.6 ± 0.2%, P < 0.01), respectively, and the reactive oxygen species (ROS) level (5.88 ± 0.90%, P < 0.01) of haemocytes and anti-bacterial activity of haemolymph (10.0 ± 2.2%, P < 0.01) all elevated dramatically at 12 h. Although the activity of lysozyme and phenoloxidase (PO) in haemolymph both declined at 48 h (93.0 ± 6.3 U mgprot(-1), 0.40 ± 0.06 U mgprot(-1), P < 0.01), superoxide dismutase (SOD) activity and GSH concentration both increased to the highest level at 24 h post treatment (99.2 ± 8.1 U mgprot(-1), 93.0 ± 6.3 nmol mgprot(-1), P < 0.01). After the collaborating treatment of LPS and SMT, the apoptosis index increased much higher from 48 h, while the increase of haemocytes phagocytosis, ROS level and haemolymph anti-bacteria activities were suppressed completely at 12 h. The declines of lysozyme and PO activity in haemolymph were reversed at 48 h, and the rise of SOD activity and GSH concentration started earlier from 3 h. These results indicated clearly that NO could participate in the scallop immunity and play a crucial role in the modulation of immune response including haemocytes apoptosis and phagocytosis, anti-bacterial activity and redox homeostasis in the haemolymph of scallop.

Regulation of lymphocytes by nitric oxide

Shortly after the identification of nitric oxide (NO) as a product of macrophages, it was discovered that NO generated by inducible NO synthase (iNOS) inhibits the proliferation of T lymphocytes. Since then, it has become clear that iNOS activity also regulates the development, differentiation, and/or function of various types of T cells and B cells and also affects NK cells. The three key mechanisms underlying the iNOS-dependent immunoregulation are (a) the modulation of signaling processes by NO, (b) the depletion of arginine, and (c) the alteration of accessory cell functions. This chapter highlights important principles of iNOS-dependent immunoregulation of lymphocytes and also reviews more recent evidence for an effect of endothelial or neuronal NO synthase in lymphocytes.

Coccidioides releases a soluble factor that suppresses nitric oxide production by murine primary macrophages

We studied the effect of the presence of Coccidioides on the production of nitric oxide (NO) by primary macrophages previously activated by IFN-γ and LPS. The fungal cells were isolated from cultures of arthroconidia that had been incubated for 24 h in a medium that supported parasitic phase growth and were co-cultured with the macrophages. These live, first-generation parasitic cells of Coccidioides, referred to as spherule initials, suppressed NO production as well as iNOS mRNA expression by activated macrophages. Phagocytosis was not required for suppression of NO. We also showed that the culture supernatant of the spherule initials was capable of suppressing NO production, and that this activity was mediated by an as yet unidentified, secreted fungal factor(s). Heat-, paraformaldehyde- or X-ray-treated spherule initials did not show this inhibitory effect. To our surprise, macrophages obtained from iNOS-deficient mice revealed phagocytic activity and killing efficiency which were comparable to that of macrophages isolated from wild type C57BL/6 mice. Although the cultured fungal pathogen can suppress NO production, this oxidative product is apparently not essential for in vitro killing of Coccidioides by activated macrophages. Our results suggest that other unidentified fungicidal mechanisms exist against Coccidioides which are apparently independent of NO production.

Estrogen regulation of nitric oxide and inducible nitric oxide synthase (iNOS) in immune cells: implications for immunity, autoimmune diseases, and apoptosis

Nitric oxide plays a central role in the physiology and pathology of diverse tissues including the immune system. It is clear that the levels of nitric oxide must be carefully regulated to maintain homeostasis. Appropriate levels of nitric oxide derived from iNOS assist in mounting an effective defense against invading microbes. Conversely, inability to generate nitric oxide results in serious, even fatal, susceptibility to infections. Further, dysregulation or overproduction of nitric oxide has been implicated in the pathogenesis of many disorders, including atherosclerosis, neurodegenerative diseases, inflammatory autoimmune diseases, and cancer. Therefore, depending upon the levels of nitric oxide generated, the potential exists for nitric oxide to behave like a "double-edged" biological sword. Taking these issues into consideration, it is thus pivotal to understand the regulation of nitric oxide. Nitric oxide is regulated by many endogenous factors including hormones such as estrogens. While the effects of estrogen on the generation of nitric oxide in non-immune tissues are relatively well documented, the effect of estrogen on iNOS/nitric oxide in immune cells is only now becoming apparent. Our laboratory has recently shown that estrogen treatment of mice markedly upregulates the levels of iNOS mRNA, iNOS protein, and nitric oxide in activated splenocytes. This upregulation of nitric oxide is in part mediated through interferon-gamma (IFN-gamma), a pro-inflammatory cytokine that is enhanced by estrogen. These findings are important considering that estrogens are not only involved in regulation of normal immune responses, but also are implicated in many autoimmune and inflammatory diseases. To date, there are no reviews on the effects of estrogen on immune tissue-derived nitric oxide and therefore this review will address this critical gap in the literature. Given the increasing importance of immune-tissue-derived iNOS in health and disease, studies on estrogen-induced regulation of iNOS may offer a better understanding of diseases and aid in devising new therapeutic interventions.

Mechanisms for impaired effector function in alveolar macrophages from marijuana and cocaine smokers

Lung macrophages provide a first line of host defense against inhaled pathogens and their function is impaired in the lungs of inhaled substance abusers. In order to investigate the mechanism for this impairment, alveolar macrophages (AM) were recovered from nonsmokers (NS), regular tobacco smokers (TS), marijuana smokers (MS), or crack cocaine smokers (CS), and evaluated for their production of nitric oxide (NO) and the role of NO as an antimicrobial effector molecule. AM from NS and TS efficiently killed Staphylococcus aureus and their antibacterial activity correlated closely with the production of nitrite and the expression of mRNA encoding for inducible nitric oxide synthase (iNOS). In contrast, AM collected from MS and CS exhibited limited antimicrobial activity that was not affected by an inhibitor of iNOS, or associated with expression of iNOS. Treatment with either granulocyte/macrophage colony-stimulating factor (GM-CSF) or interferon-gamma restored the ability of these cells to produce NO and to kill bacteria. These findings confirm a significant role for NO as an antibacterial effector molecule used by normal human AM and suggest that this host defense mechanism is suppressed by habitual exposure to inhaled marijuana or crack cocaine in vivo.

Translational control of inducible nitric oxide synthase by IL-13 and arginine availability in inflammatory macrophages

Inducible NO synthase (iNOS) and its generation of NO from L-arginine are subject to transcriptional as well as posttranscriptional control by cytokines. In this study, we describe a novel, translational mechanism of iNOS regulation by arginine availability. Using mouse inflammatory peritoneal macrophages stimulated with IFN-gamma plus LPS, we demonstrate that the suppression of iNOS protein, which is observed after a 16-h (but not after a 6-h) pretreatment with IL-13, despite an unaltered iNOS mRNA level, results from arginine depletion by arginase. The addition of arginase inhibitors (in the pretreatment phase) or of arginine (in the stimulation phase) completely blocked the down-regulation of iNOS protein by IL-13. The rescuing effect of arginine supplementation was not due to a positive feedback regulation of iNOS expression via enhanced production of NO. A striking suppression of iNOS protein (but not of iNOS mRNA) was also seen, when IL-13 was replaced by purified arginase or when macrophages were stimulated with IFN-gamma/LPS in arginine-free medium. Arginine deficiency specifically impaired the de novo synthesis and the stability of iNOS protein, but did not affect the production of TNF and the overall protein synthesis of the macrophages. From these results, we conclude that arginine not only functions as a substrate for iNOS, but is also critical for maintaining normal levels of iNOS protein in cytokine-stimulated macrophages.

The role of inducible nitric oxide synthase in a murine acute hepatitis B virus (HBV) infection model induced by hydrodynamics-based in vivo transfection of HBV-DNA

BACKGROUND/AIMS

Inducible nitric oxide synthase (iNOS) is found to have antiviral activity. Its role is evaluated using a murine acute hepatitis B virus (HBV) infection model.

METHODS

pHBV3.6 plasmid containing HBV genome was injected into mice by hydrodynamics-based in vivo transfection. HBV antigenemia and serum HBV-DNA were detected by enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction, respectively. HBV replication in liver was analyzed by Northern and Southern blot. Intrahepatic leukocytes were isolated and analyzed with flow cytometry.

RESULTS

After hydrodynamics injection of pHBV3.6, HBV genome was synthesized in the liver and HBV-DNA, as well as hepatitis B surface antigen and hepatitis B e antigen were secreted into the blood. Anti-HBV antibody responses developed afterward. A murine acute HBV infection model was established with hydrodynamics injection of non-transponase based HBV-DNA. Using this protocol in iNOS deficient or wild type B6 mice, the level of HBV transcript, replicative intermediate, and antigenemia were higher in iNOS(-/-) than in B6 mice. The intrahepatic leukocytes in iNOS(-/-) mice were also affected after transfection.

CONCLUSIONS

Our data suggests that the iNOS expression not only affects the HBV clearance, but also modulates the infiltrating leukocytes response to HBV antigens.

Inducible nitric oxide synthase inhibitors prolonged the survival of skin xenografts through selective down-regulation of pro-inflammatory cytokine and CC-chemokine expressions

To elucidate the possible immunoregulatory role of nitric oxide (NO) in cellular xenograft rejection we performed rat-to-mouse skin xenotransplantation. The rat skin engrafted mice were treated with the inducible NO synthase (iNOS) inhibitors, aminoguanidine (AMG, 200 mg/kg) and NG-nitro-L-arginine methyl ester (L-NAME, 60 mg/kg) every other day until rejection. Skin xenograft survival was monitored and immune cell infiltration and intragraft cytokine and chemokine mRNA expressions were analyzed 7 days after grafting. Compared with the control mice, the AMG- and L-NAME treated mice showed delayed xenograft rejection by approximately 3 days (8.9 +/- 0.7 days vs. 11.7 +/- 1.2 and 12.0 +/- 0.9 days, respectively). Infiltrations of CD11b+, MOMA-2+ cells and neutrophils were significantly reduced in both AMG- and L-NAME treated graft but CD4+ and CD8+ cells were not. The expression of cytokines such as IL-1beta, IL-2, IL-6, IL-12 and IFN-gamma in AMG- and L-NAME treated grafts were significantly decreased (P<0.01), whereas IL-10, TNF-alpha and TGF-beta1 were unchanged or enhanced. Additionally, the expressions of CC-chemokines, such as RANTES and MIP-1alpha, were significantly reduced (P<0.01) whereas the expressions of CXC-chemokines, such as IP-10 and MIG, were unchanged. These results imply that prolonged rat-to-mouse skin xenograft survival by iNOS inhibitors may be due to the selective inhibition of pro-inflammatory cytokines and chemokines and suggest the possible regulatory role of NO in cytokine and chemokine expressions during xenotransplant rejection.

Involvement of lipopolysaccharide related receptors and nuclear factor kappa B in differential expression of inducible nitric oxide synthase in chicken macrophages from different genetic backgrounds

Macrophages from Cornell K-strain chickens (B(15)B(15)) are hyper and from GB2 chickens (B(6)B(6)) are hypo-responders to LPS-mediated inducible NOS (iNOS) expression and activity. The molecular mechanism(s) responsible for this differential expression is not yet fully understood. We have previously reported that macrophages from K (iNOS hyper-responder) and GB2 (iNOS hypo-responder) chickens differ in constitutive expression of TLR4 but not in CD14 molecules. The objectives of the current study was to determine if the iNOS differences between K and GB2 macrophages are possibly due to differential expression of LPS-induced TLR4, CD14 and/or nuclear factor kappa B (NF kappa B). The results showed that Sephadex-elicited, adherence purified K macrophages expressed more inducible TLR4 and CD14 receptors (P<0.05) at 6 and 12h post-LPS stimulation than GB2 macrophages as measured by flow cytometry. In addition, pre-incubation of macrophages from a transformed chicken macrophage cell line, MQ-NCSU, with 50 microg/ml anti-CD14 and anti-TLR4 antibodies significantly reduced where as pre-incubation with 100 microg/ml completely blocked LPS-mediated iNOS activity as measured by nitrite levels. Furthermore, the amount of nuclear bound NF kappa B was found to be significantly greater in K than in GB2 macrophages at 3 min post-LPS stimulation. This nuclear localization of NF kappa B as well as iNOS activity was completely inhibited by pretreatment of macrophages with 50 micro M MG132, a proteosome inhibitor, both in K and GB2 macrophages. Taken together, these findings suggest that a differential and perhaps more stronger LPS-mediated signaling via CD14, TLR4 and NF kappa B is responsible for the heightened iNOS gene induction in K-strain (hyper-responder) macrophages than in GB2 (hypo-responder) chickens.

Nitric oxide and the regulation of gene expression

During the past 15 years, nitric oxide (NO) and NO synthases have become an important research topic in cellular and molecular biology. NO is produced by many if not all mammalian cells and fulfils a broad spectrum of signaling functions in physiological and pathophysiological processes. In this review, recent advances in our understanding of the mechanisms by which NO regulates the expression of eukaryotic genes will be summarized. The currently available data illustrate that NO has multiple molecular targets: it can not only directly influence the activity of transcription factors but also modulates upstream signaling cascades, mRNA stability and translation, as well as the processing of the primary gene products.

Reactive oxygen and reactive nitrogen intermediates in innate and specific immunity

Nitric oxide, nitric oxide derivatives and reactive oxygen intermediates are toxic molecules of the immune system which contribute to the control of microbial pathogens and tumors. There is recent evidence for additional functions of these oxygen metabolites in innate and adaptive immunity; these functions include the modulation of the cytokine response of lymphocytes and the regulation of immune cell apoptosis, as well as immunodeviating effects. Components of several signal transduction pathways have been identified as intracellular targets for reactive nitrogen and oxygen intermediates.