Repeated induction of nitric oxide synthase and leishmanicidal activity in murine macrophages

Guanylate Binding Proteins Restrict Leishmania donovani Growth in Nonphagocytic Cells Independent of Parasitophorous Vacuolar Targeting

Interferon (IFN)-inducible guanylate binding proteins (GBPs) play important roles in host defense against many intracellular pathogens that reside within pathogen-containing vacuoles (PVs). For instance, members of the GBP family translocate to PVs occupied by the protozoan pathogen Toxoplasma and facilitate PV disruption and lytic parasite killing. While the GBP defense program targeting Toxoplasma has been studied in some detail, the role of GBPs in host defense to other protozoan pathogens is poorly characterized. Here, we report a critical role for both mouse and human GBPs in the cell-autonomous immune response against the vector-borne parasite Leishmania donovani Although L. donovani can infect both phagocytic and nonphagocytic cells, it predominantly replicates inside professional phagocytes. The underlying basis for this cell type tropism is unclear. Here, we demonstrate that GBPs restrict growth of L. donovani in both mouse and human nonphagocytic cells. GBP-mediated restriction of L. donovani replication occurs via a noncanonical pathway that operates independent of detectable translocation of GBPs to L. donovan-containing vacuoles (LCVs). Instead of promoting the lytic destruction of PVs, as reported for GBP-mediated killing of Toxoplasma in phagocytic cells, GBPs facilitate the delivery of L. donovani into autolysosomal-marker-positive compartments in mouse embryonic fibroblasts as well as the human epithelial cell line A549. Together our results show that GBPs control a novel cell-autonomous host defense program, which renders nonphagocytic cells nonpermissible for efficient Leishmania replication.IMPORTANCE The obligate intracellular parasite Leishmania causes the disease leishmaniasis, which is transmitted to mammalian hosts, including humans, via the sandfly vector. Following the bite-induced breach of the skin barrier, Leishmania is known to live and replicate predominantly inside professional phagocytes. Although Leishmania is also able to infect nonphagocytic cells, nonphagocytic cells support limited parasitic replication for unknown reasons. In this study, we show that nonphagocytic cells possess an intrinsic property to restrict Leishmania growth. Our study defines a novel role for a family of host defense proteins, the guanylate binding proteins (GBPs), in antileishmanial immunity. Mechanistically, our data indicate that GBPs facilitate the delivery of Leishmania into antimicrobial autolysosomes, thereby enhancing parasite clearance in nonphagocytic cells. We propose that this GBP-dependent host defense program makes nonphagocytic cells an inhospitable host cell type for Leishmania growth.

Impact of primary mouse macrophage cell types on Leishmania infection and in vitro drug susceptibility

Primary mouse macrophages are frequently used to provide an in vitro intracellular model to evaluate antileishmanial drug efficacy. The present study compared the phenotypic characteristics of Swiss, BALB/c, and C57BL/6 mouse bone marrow-derived macrophages and peritoneal exudate cells using different stimulation and adherence protocols upon infection with a Leishmania infantum laboratory strain and two clinical isolates. Evaluation parameters were susceptibility to infection, permissiveness to amastigote multiplication, and impact on drug efficacy. Observed variations in infection of peritoneal exudate cells can mostly be linked to changes in the inflammatory cytokine profiles (IL-6, TNF-α, KC/GRO) rather than to differences in initial production of nitric oxide and reactive oxygen species. Optimization of the cell stimulation and adherence conditions resulted in comparable infection indices among peritoneal exudate cells and the various types of bone marrow-derived macrophages. BALB/c-derived bone marrow-derived macrophages were slightly more permissive to intracellular amastigote replication. Evaluation of antileishmanial drug potency in the various cell systems revealed minimal variation for antimonials and paromomycin, and no differences for miltefosine and amphotericin B. The study results allow to conclude that drug evaluation can be performed in all tested primary macrophages as only marginal differences are observed in terms of susceptibility to infection and impact of drug exposure. Combined with some practical considerations, the use of 24-h starch-stimulated, 48-h adhered, Swiss-derived peritoneal exudate cells can be advocated as an efficient, reliable, relatively quick, and cost-effective tool for routine drug susceptibility testing in vitro whenever the use of primary cells is feasible.

Effect of acute endotoxin tolerance on NO production by isolated hepatic parenchymal and nonparenchymal cells and alveolar macrophages in rats

The changes in NO production induced by endotoxin (LPS) tolerance are controversial. The aim of this study was to explore modulation of NO production by LPS tolerance in different liver cell types and alveolar macrophages. Such cells were studied in three groups of male Sprague Dawley rats: non-tolerant rats (sal-LPS) received saline or no treatment 48 h before a 3 mg/kg LPS injection, tolerant rats received low dose LPS (0.5 mg/kg) 48 h before a second injection of saline (LPS-sal) or LPS 3 mg/kg (LPS-LPS). All injections were delivered i.v. Animals were studied 1 and 6 h after the second injection. NO production (assessed by nitrite release) by hepatocytes, Kupffer cells, endothelial cells and alveolar macrophages was simultaneously determined after 20 h of culture in the presence or in the absence of LPS, interferon-y (IFN) or both. Basal NO production by hepatocytes of tolerant and nontolerant LPS injected rats was high 1 h after the second injection, and was dramatically reduced 6 h after the second injection. Hepatocytes of tolerized LPSinjected (LPS-LPS) rats were significantly less sensitive to in vitro stimulation by LPS and IFN at 1 h than hepatocytes of tolerized saline-injected rats and this difference disappeared by 6 h. In Kupffer cells of tolerant rats 6 h after the second LPS injection, basal NO generation was significantly less than in nontolerant rats. In both cell types of tolerant LPS-LPS rats, in vitro stimulated NO production was moderately upregulated at 1 h and then highly upregulated at 6 h, whereas in nontolerant (sal-LPS) animals, stimulated NO production was only slightly upregulated or not at all. Sensitivity to LPS and IFN stimulation of Kupper cells of LPS-LPS rats was not different from Kupffer cells of LPS-sal rats at 1 h, but became significantly higher at 6 h relative to both LPS-sal and sal-LPS animals. In endothelial cells of tolerant saline-injected (LPS-sal) rats, basal NO production was significantly less than in the sal-LPS group both at 1 and 6 h after the second injection. In endothelial cells of tolerant LPS-LPS animals, a significant upregulation of stimulated NO production higher than in the other groups was observed only at 1 h. No difference was evident in basal or stimulated NO production by alveolar macrophages of the different treatment groups, except for a significant increase in basal NO production in tolerant rats (LPS-LPS) at 6 h relative to 1 h after the second LPS injection.

Genetic Manipulation of Leishmania donovani to Explore the Involvement of Argininosuccinate Synthase in Oxidative Stress Management

Reactive oxygen and nitrogen species (ROS and RNS) produced by the phagocytic cells are the most common arsenals used to kill the intracellular pathogens. However, Leishmania, an intracellular pathogen, has evolved mechanisms to survive by counterbalancing the toxic oxygen metabolites produced during infection. Polyamines, the major contributor in this anti-oxidant machinery, are largely dependent on the availability of L-arginine in the intracellular milieu. Argininosuccinate synthase (ASS) plays an important role as the rate-limiting step required for converting L-citrulline to argininosuccinate to provide arginine for an assortment of metabolic processes. Leishmania produce an active ASS enzyme, yet it has an incomplete urea cycle as it lacks an argininosuccinate lyase (ASL). There is no evidence for endogenous synthesis of L-arginine in Leishmania, which suggests that these parasites salvage L-arginine from extracellular milieu and makes the biological function of ASS and the production of argininosuccinate in Leishmania unclear. Our previous quantitative proteomic analysis of Leishmania promastigotes treated with sub-lethal doses of ROS, RNS, or a combination of both, led to the identification of several differentially expressed proteins which included ASS. To assess the involvement of ASS in stress management, a mutant cell line with greatly reduced ASS activity was created by a double-targeted gene replacement strategy in L. donovani promastigote. Interestingly, LdASS is encoded by three copies of allele, but Western blot analysis showed the third allele did not appear to express ASS. The free thiol levels in the mutant LdASS-/-/+ cell line were decreased. Furthermore, the cell viability in L-arginine depleted medium was greatly attenuated on exposure to different stress environments and was adversely impacted in its ability to infect mice. These findings suggest that ASS is important for Leishmania donovani to counterbalance the stressed environments encountered during infection and can be targeted for chemotherapeutic purpose to treat visceral leishmaniasis.

Leishmania eukaryotic initiation factor (LeIF) inhibits parasite growth in murine macrophages

The leishmaniases constitute neglected global public health problems that require adequate control measures, prophylactic clinical vaccines and effective and non-toxic drug treatments. In this study, we explored the potential of Leishmania infantum eukaryotic initiation factor (LieIF), an exosomal protein, as a novel anti-infective therapeutic molecule. More specifically, we assessed the efficacy of recombinant LieIF, in combination with recombinant IFN-γ, in eliminating intracellular L. donovani parasites in an in vitro macrophage model. J774A.1 macrophages were initially treated with LieIF/IFN-γ prior to in vitro infection with L. donovani stationary phase promastigotes (pre-infection treatment), and resistance to infection was observed 72 h after infection. J774A.1 macrophages were also treated with LieIF/IFN-γ after L. donovani infection (post-infection treatment), and resistance to infection was also observed at both time points tested (19 h and 72 h) after infection. To elucidate the LieIF/IFN-γ-induced mechanism(s) that mediate the reduction of intracellular parasite growth, we examined the generation of potent microbicidal molecules, such as nitric oxide (NO) and reactive oxygen species (ROS), within infected macrophages. Furthermore, macrophages pre-treated with LieIF/IFN-γ showed a clear up-regulation in macrophage inflammatory protein 1α (MIP-1α) as well as tumor necrosis factor alpha (TNF-α) expression. However, significant different protein levels were not detected. In addition, macrophages pre-treated with LieIF/IFN-γ combined with anti-TNF-α monoclonal antibody produced significantly lower amounts of ROS. These data suggest that during the pre-treatment state, LieIF induces intramacrophage parasite growth inhibition through the production of TNF-α, which induces microbicidal activity by stimulating NO and ROS production. The mechanisms of NO and ROS production when macrophages are treated with LieIF after infection are probably different. Overall, these results indicate that LieIF is a good candidate for use as an anti-leishmanial molecule.

Shared signaling systems in myeloid cell-mediated muscle regeneration

Much of the focus in muscle regeneration has been placed on the identification and delivery of stem cells to promote regenerative capacity. As those efforts have advanced, we have learned that complex features of the microenvironment in which regeneration occurs can determine success or failure. The immune system is an important contributor to that complexity and can determine the extent to which muscle regeneration succeeds. Immune cells of the myeloid lineage play major regulatory roles in tissue regeneration through two general, inductive mechanisms: instructive mechanisms that act directly on muscle cells; and permissive mechanisms that act indirectly to influence regeneration by modulating angiogenesis and fibrosis. In this article, recent discoveries that identify inductive actions of specific populations of myeloid cells on muscle regeneration are presented, with an emphasis on how processes in muscle and myeloid cells are co-regulated.

Nitric oxide production disorders in leukocytes of patients with recurrent furunculosis

AIM

The propensity for certain individuals to develop staphylococcal recurrent furunculosis (RF) is not fully understood. But among the reasons of its development the immune system dysfunctions are described. As in the staphylococcus elimination the main role is played by neutrophils, the objective of this study was to determine nitric oxide (NO) and reactive oxygen species (ROS) production by polymo rphonuclear leukocytes (PMNs) of patients with RF and to compare them with the response of normal cells to stimulation.

MATERIALS AND METHODS

The spontaneous and pyrogenal-stimulated nitric oxide production was evaluated in leukocyte cell cultures by Griess reaction, and ROS generation was determined in the stimulated and unstimulated NBT-test.

RESULTS

In this study we have demonstrated that leukocytes of healthy subjects respond on stimulation by the increase of both NO and ROS production. In contrast, leukocytes of patients with RF react by depression of NO formation at stimulation, and are characterized by decrease of ROS production reserve with the increasing of spontaneous ROS generation. Described disorders are revealed in the remission period as well as at exacerbation of furunculosis.

CONCLUSION

The present study suggests that leukocytes of patients with RF have stable defect of stimulated NO production increase, which can be the reason for recurrent and severe course of furunculosis.

Nitric oxide radicals in leucocytes and vaginal washes of Trichomonas vaginalis -infected symptomatic and asymptomatic women

The clinical spectrum of Trichomonas vaginalis infection varies from asymptomatic to mild, moderate or severe vaginitis. Nitric oxide and other reactive nitrogen radicals produced by immune effector cells are important cytotoxic and cytostatic mediators against several microorganisms including parasites. In the present study, inducible nitric oxide synthase (iNOS) and reactive nitrogen intermediates (RNI) were determined in leucocyte cultures (stimulated with T. vaginalis in vitro) and vaginal washes (VWs) of 22 symptomatic and 20 asymptomatic T. vaginalis-infected and 20 healthy women by immunoblotting and Griess method respectively. The iNOS protein was detected in leucocytes and VWs of all the symptomatic and asymptomatic women, but was not detected in any of the samples from healthy women. Mean iNOS protein band intensity was significantly higher in leucocytes as compared to VWs (P<0.001) of both symptomatic and asymptomatic women and was also higher in leucocytes of asymptomatic as compared to symptomatic women (P<0.05). Mean RNI concentration was also significantly higher in leucocytes (P<0.01) and VWs (P<0.05) of asymptomatic as compared to symptomatic women, and was also higher in samples of infected as compared to healthy women (P<0.001). These results suggest that reactive nitrogen radicals may have a role in limiting T. vaginalis infection in asymptomatic women.

Toxocara canis: Search for a potential drug amongst β-carboline alkaloids—in vitro and mouse studies

The goal of this study was to search for new treatments for Toxocara canis using both in vitro and in vivo experiments. We specifically looked for a treatment for T. canis larva migrans, and examined beta-carboline alkaloids (17 compounds) with various structural modifications, both in in vitro and in vivo experiments. In the in vitro experiments, screening for nematocidal activity on the T. canis second stage larvae, cytotoxic activity, and immune activity in the host were undertaken. Compound 17 was selected, as it exhibited nematocidal activity for T. canis larvae and did not have any cytotoxic or immunosuppressive activity in the host. The effectiveness of compound 17 was then examined using T. canis larvae infected mice in in vivo experiments. To evaluate the anthelmintic effect, the relative mobility value for the larvae was examined in addition to the number of larvae in the brain, skeletal muscle, and liver. Compound 17 was also examined in both free and liposome-entrapped (LE) forms. Polyethylene glycol (PEG)-LE compound 17 showed an anthelmintic effect in which the number of larvae in the brain was decreased compared free albendazole. PEG-LE compound 17 also effectively suppressed the mobility of the larva in brain and skeletal muscle. The experimental procedure employed assisted in the discovery of this potential candidate and is a promising approach for finding alternative therapeutic regimens for T. canis larva migrans.

Enhanced release of prostaglandin D2 during re-incubation of RAW 264.7 macrophage-like cells after treatment of both lipopolysaccharide and non-steroidal anti-inflammatory drugs

RAW 264.7 macrophage-like cells are known to release prostaglandins (PGs), mainly PGD(2) to the culture medium after lipopolysaccharide (LPS)-treatment. This release was inhibited by non-steroidal anti-inflammatory drugs (NSAIDs), which are known to inhibit prostaglandin H(2) synthase (PGHS) activity. In this study, we examined the effect of removal of NSAID after induction of PGHS with LPS, on the release of PGs, which has not been studied well. Re-incubation of RAW 264.7 cells after treatment of both LPS and NSAIDs resulted in enhanced release of PGD(2) compared with the cells pretreated with LPS alone. Besides, PGHS activity was detectable in these cell homogenates and the amount of PGHS-2 protein showed similar changes to PGD(2) release. However, addition of NSAIDs again in the re-incubation period almost completely inhibited the PGD(2) release but increased the amount of PGHS-2 protein to the higher levels. Various types of NSAIDs used in this study showed similar effects on the changes in PGD(2) release and PGHS-2 protein amounts, except those on PGHS activity in cell homogenates; while indomethacin, aspirin, and NS-398 inhibited it, but nimesulide and acetaminophen did not. These results seem to suggest an importance for the caution that the enhanced induction of PGHS-2 protein and the concomitant release of PGs release would occur after removal of the NSAID not only from the medium in in vitro experiments but also from therapeutic prescription.

Two linked genes of Leishmania infantum encode tryparedoxins localised to cytosol and mitochondrion

Tryparedoxins are components of the hydroperoxide detoxification cascades of Kinetoplastida, where they mediate electron transfer between trypanothione and a peroxiredoxin, which reduces hydroperoxides and possibly peroxynitrite. Tryparedoxins may also be involved in DNA synthesis, by their capacity to reduce ribonucleotide reductase. Here we report on the isolation of two tryparedoxin genes from Leishmania infantum, Li7XN1 and LiTXN2, which share the same genetic locus. These genes are both single copy and code for two active tryparedoxin enzymes, LiTXN1 and LiTXN2, with different biochemical and biological features. LiTXN1 is located to the cytosol and is upregulated in the infectious forms of the parasite, strongly suggesting that it might play an important role during infection. LiTXN2 is the first mitochondrial tryparedoxin described in Kinetoplastida. Biochemical assays performed on the purified recombinant proteins have shown that LiTXN1 preferentially reduces the cytosolic L. infantum peroxiredoxins, LicTXNPx1 and LicTXNPx2, whereas LiTXN2 has a higher specific activity for a mitochondrial peroxiredoxin, LimTXNPx. Kinetically, the two tryparedoxins follow a ping-pong mechanism and show no saturation. We suggest that LiTXN1 and LiTXN2 are part of two distinct antioxidant machineries, one cytosolic, the other mitochondrial, that complement each other to ensure effective defence from several sources of oxidants throughout the development of L. infantum.

Hyperoxia causes inducible nitric oxide synthase-mediated cellular damage to the immature rat brain

Relative hyperoxia is a condition frequently encountered in premature infants, either spontaneously or during treatment in the Neonatal Intensive Care Unit. The effects of high inspiratory oxygen concentrations on immature brain cells and their signaling cascades are largely unknown. The aim of the study was to investigate the effect of hyperoxia on the amount and topographic distribution of iNOS-expression (inducible nitric oxide synthase) in the immature rat brain, and to localize hyperoxia-induced formation of peroxynitrite as a potential marker of cellular damage to immature cerebral structures. Seven-day-old Wistar rat pups were exposed to >80% oxygen for 24 h and were then transcardially perfused. Following paraformaldehyde fixation, brains were paraffin-embedded and immunohistochemically stained for iNOS and nitrotyrosine. iNOS protein was quantified by Western blot; iNOS mRNA expression was studied by RT-PCR. Total brain iNOS mRNA was up-regulated, demonstrating a peak at 6 h following the onset of hyperoxia. Immunohistochemical staining was predominantly observed in microglial cells of hippocampus and frontal cortex with some iNOS reactivity in endothelial and perivascular cells. Nitrotyrosine staining was positive in apical dendrites of neurons in the frontal cortex. There was no positive staining for iNOS or nitrotyrosine in control animals. Hyperoxia causes iNOS mRNA and protein up-regulation in microglial cells of the immature rat brain. Positive neuronal nitrotyrosine staining indicates formation of peroxynitrite with potential deleterious effects for immature cellular structures in the neonatal brain.

Expression of inducible nitric oxide synthase in human umbilical vein endothelial cells during primary culture

The adaptive response of endothelial cells to stress may lead to the upregulation of nitric oxide (NO) production. Herein, we report inducible nitric oxide synthase (iNOS) induction in primary cultures of human umbilical vein endothelial cells (HUVEC). The enzyme expression was earlier observed in 12-h cultures, reaching maximal levels after 3 days and decreasing when cells become confluent. The time course of NO production by HUVEC paralleled iNOS expression during the whole culture period, indicating that enzyme was functionally active. Conversely, iNOS induction could not be further detected in HUVEC subcultures passed once from cells presenting maximal levels of iNOS expression in the primary culture. Induction of iNOS in HUVEC was not related to lipopolysaccharide contamination, since the enzyme expression was not affected in the presence of polymyxin B added to primary cultures. Further analysis showed that aminoguanidine, a specific iNOS inhibitor, did not affect cell proliferation, suggesting that the NO produced by HUVEC may not be directly related to cell growth. Platelet endothelial cell adhesion molecule-1 expression was upregulated during cell confluence, in contrast to the decrease of iNOS expression and activity. The data suggest that iNOS expression may be a molecular mechanism mediating the adaptive response of endothelial cells to culture environment.

Immunohistochemical detection and distribution of inducible nitric oxide synthase in pigs naturally infected with Actinobacillus pleuropneumoniae

Inducible nitric oxide synthase (iNOS) protein was detected immunohistochemically in formalin-fixed, paraffin wax-embedded lung tissues from 10 natural cases of porcine pleuropneumonia. Positive cells typically exhibited a red reaction product without background staining. Labelling of iNOS protein was intense in "oat cells", the clustered leucocytes with streaming nuclear chromatin that are a characteristic histological feature of porcine pleuropneumonia. Macrophages and neutrophils within alveolar spaces but not within blood vessels consistently showed iNOS labelling, but such labelling was minimal in non-lesional lung of Actinobacillus pleuropneumoniae -infected pigs and in normal lung from control pigs. The results suggest that iNOS plays a role in pathophysiological processes during A. pleuropneumoniae infection.

Oxidative responses of human and murine macrophages during phagocytosis of Leishmania chagasi

Leishmania chagasi, the cause of South American visceral leishmaniasis, must survive antimicrobial responses of host macrophages to establish infection. Macrophage oxidative responses have been shown to diminish in the presence of intracellular leishmania. However, using electron spin resonance we demonstrated that murine and human macrophages produce O2-during phagocytosis of opsonized promastigotes. Addition of the O2- scavenger 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl to cultures resulted in increased infection, suggesting that O2- enhances macrophage leishmanicidal activity. The importance of NO. produced by inducible NO synthase (iNOS) in controlling murine leishmaniasis is established, but its role in human macrophages has been debated. We detected NO. in supernatants from murine, but not human, macrophages infected with L. chagasi. Nonetheless, the iNOS inhibitor N(G)-monomethyl-L-arginine inhibited IFN-gamma-mediated intracellular killing by both murine and human macrophages. According to RNase protection assay and immunohistochemistry, iNOS mRNA and protein were expressed at higher levels in bone marrow of patients with visceral leishmaniasis than in controls. The iNOS protein also increased upon infection of human macrophages with L. chagasi promastigotes in vitro in the presence of IFN-gamma. These data suggest that O2- and NO. each contribute to intracellular killing of L. chagasi in human and murine macrophages.

Inhibition of prostaglandin synthesis by nitric oxide in RAW 264.7 macrophages

Multiple effects of nitric oxide (NO) were revealed on the inhibition of prostaglandin (PG) synthesis by a macrophage-like cell line, RAW 264.7 cells, treated with lipopolysaccharide (LPS). NO-generating reagent, N-ethyl-2-(1-ethyl-2-hydroxy-2-nitrosohydrazino)ethanamine (NOC 12), inhibited the release of PG from cells with LPS treatment at higher concentrations although it stimulated the release at 50 microM. PGH synthase (PGHS) activity in the microsome fraction of the LPS-treated cells was inhibited by (+/-)-(E)-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexeneamine (NOR 1), another NO-generating reagent, dose dependently. NOC 12 also dose dependently inhibited PG synthesis from exogenous arachidonic acid in those cells. On the other hand, NOC 12 increased PGHS-2 mRNA, while it increased the PGHS-2 protein at concentrations lower than 200 microM or decreased it at higher concentrations. These results suggest that the effect of NO on PGs synthesis in LPS-treated macrophage cells is mainly due to the balance of its stimulations of the transcriptional and/or translational expression of PGHS-2 and the inhibition of the induced PGHS-2 activity.

A description of parasite-harbouring cells in localized lymphadenitis in dry type cutaneous leishmaniasis

Lymphadenitis with or without dry-type cutaneous leishmaniasis is rare. The lesion might self heal or show excellent response to antimonial therapy. Routine histopathological changes of localized leishmaniasis lymphadenitis are non-caseating to suppurative granulomata mostly in paracortical areas, some with extension to germinal centres, medullary cords and/or pericapsular spaces which have to be distinguished from other causes of lymphadenitis such as tuberculosis, cat-scratch disease and toxoplasmosis. Dense lymphoplasmocytic infiltrate was observed surrounding the necrotizing granuloma together with dense capsular fibrosis with multiple granulomata in subcapsular and pericapsular areas. Immunostaining of lymph nodes showed that a few macrophages were harbouring Leishman bodies. Dispersed Langerhans cells were also harbouring Leishman bodies in the parasitophorous vacuoles between their cytoplasmic pseudopods. In conclusion multiple noncaseating to suppurative granulomata with dense pericapsular and capsular granulomo-sclerotic changes should be considered in the differential diagnosis of leishmaniasis lymphadenitis.

Lipopolysaccharide tolerance and ethanol modulate hepatic nitric oxide production in a gender-dependent manner

This study was directed at the role of tolerance to endotoxin (lipopolysaccharide, LPS) and ethanol (EtOH) intoxication in modulating hepatic nitric oxide (NO) production, and the demonstration of gender differences. Previous studies demonstrated that tolerance to either LPS or EtOH was associated with reduced hepatic production of superoxide anions. We now tested the hypothesis that the reduced hepatic production of superoxide anions during tolerance to LPS and the altered response to EtOH are accompanied by increased sensitivity of hepatic NO release to stimulation. Age-matched male and female Sprague-Dawley rats were made tolerant to LPS by an i.v. injection of LPS (0.5 or 0.45 mg/kg) 2 days prior to an in vivo EtOH infusion for 3 h (LPS-EtOH group). Control groups were saline-pretreated, saline-infused; saline-pretreated, EtOH-infused; and LPS-pretreated, saline-infused. At the end of the infusion, isolated hepatocytes, Kupffer, and sinusoidal endothelial cells were cultured for 20 h for subsequent measurement of basal (spontaneous) and in vitro-stimulated nitrite release. LPS-tolerance resulted in significantly enhanced stimulated NO production by hepatocytes and Kupffer cells in both male and female rats. EtOH abolished this priming effect in hepatocytes from male, but not from female rats. The priming effect was markedly diminished by EtOH in Kupffer cells of female rats only. LPS-tolerance increased NO production by stimulated endothelial cells of males, and decreased NO production by cells of females. EtOH infusion did not influence NO production by endothelial cells from male rats and it reversed the LPS-tolerance-induced inhibition in females. These data demonstrate that modulation by LPS-tolerance of hepatic NO release in EtOH-treated rats leads to enhanced stimulated NO production, while hepatic superoxide anion release was previously shown to be reduced within the same time frame. Since NO is able to scavenge superoxide, the LPS-tolerance-induced alterations in the EtOH effects on NO production may have a potential significance in modulating - in a time-dependent manner - oxidative injury associated with LPS and acute EtOH intake.

2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) inhibits nitric oxide production in cultured murine astrocytes

The level of nitrite accumulation in the culture media of astrocytes activated with lipopolysaccharide (LPS) and interferon-gamma (IFN) was decreased by pretreatment of cells with LY294002, a quercetin derivative developed for phosphatidylinositol-3-kinase (PI3K) inhibitor, in a dose-dependent manner. The expression of iNOS mRNA in the astrocytes was inhibited by LY294002, as revealed by reverse transcriptional polymerase chain reaction and agarose gel electrophoresis. The catalytic activity of astrocytic iNOS was also inhibited by LY294002. On the other hand, wortmannin which was known to enhance endotoxin-induced NO production in macrophages by inhibiting PI3K did not cause any significant change in the NO production and iNOS mRNA expression of the astrocytes. These results suggest that LY294002 suppresses NO production in the astrocytes through not only the inhibition of iNOS mRNA expression but also the inhibition of the iNOS activity and that PI3K is not involved in the inhibitory actions of LY294002.pc 1999 Academic Press@p$hr

Effect of therapeutic concentrations of nitric oxide on bacterial growth in vitro

OBJECTIVES

Besides its vasodilative actions, nitric oxide (NO) is also involved in host defense on a cellular level. We studied the antimicrobial properties of NO in concentrations used with inhaled NO therapy for the treatment of pulmonary hypertension in neonates.

DESIGN

In vitro study of bacterial growth of five species, with and without NO exposure.

SETTING

Level IV neonatal intensive care unit at a university children's hospital.

SUBJECTS

In vitro bacterial cultures.

INTERVENTIONS

We tested ten different strains of five bacterial species (Staphylococcus aureus, Staphylococcus epidermidis, group B streptococcus [GBS/Streptococcus agalactiae], Escherichia coli, and Pseudomonas aeruginosa), derived from the tracheal isolates of ventilated premature and term infants. Cultures were exposed to three different concentrations of NO (40, 80, and 120 parts per million [ppm]) and bacterial growth was compared with the same strains incubated in ambient air for 24 hrs. After incubation (with or without NO), colony-forming units were counted.

MEASUREMENTS AND MAIN RESULTS

Bacterial growth of S. aureus, E. coli, and P. aeruginosa was not reduced with the NO concentrations applied. The number of colony-forming units of S. aureus increased at 80 ppm of NO. Growth of S. epidermidis and GBS was significantly affected at 120 ppm, resulting in decreased numbers of colony-forming units as compared with controls exposed to ambient air.

CONCLUSIONS

We conclude that NO has a selective bacteriostatic effect on some of those bacteria most commonly cultured in tracheal specimens of premature infants and neonates. This effect appears to be dose-dependent and occurs in the upper range of dosages used with inhaled NO therapy. However, in the range of dosages applied in ongoing controlled trials of inhaled NO in neonates and premature infants (1 to 80 ppm), a bacteriostatic effect of NO is not to be expected.

Growth and viability of macrophages continuously stimulated to produce nitric oxide

Deregulated production of nitric oxide (NO) has been implicated in the development of certain human diseases, including cancer. We sought to assess the damaging potential of NO produced under long-term conditions through the development of a suitable model cell culture system. In this study, we report that when murine macrophage-like RAW264.7 cells were exposed continuously to bacterial lipopolysaccharide (LPS) or mouse recombinant interferon-gamma (IFN-gamma) over periods of 21-23 days, they continued to grow, but with doubling times 2 to 4 times, respectively, longer than the doubling time of unstimulated cells. Stimulated cells produced NO at rates of 30 to 70 nmol per million cells per day throughout the stimulation period. Within 24 hr after removal of stimulant, cells resumed exponential growth. Simultaneous exposure to LPS and IFN-gamma resulted in decreased cell number, which persisted for 2 days after removal of the stimulants. Exponential growth was attained only after an additional 4 days. Addition of N-methyl-L-arginine (NMA), an NO synthase inhibitor, to the medium inhibited NO production by 90% of all stimulated cells, partially reduced doubling time of cells stimulated with LPS or IFN-gamma, and partially increased viability and growth rates in those exposed to both LPS and IFN-gamma. However, when incubated with LPS and IFN-gamma at low densities both in the presence and in the absence of NMA, cells grew at a rate slower than that of unstimulated cells, with no cell death, and they resumed exponential growth 24 hr after removal of stimulants. Results from cell density experiments suggest that macrophages are protected from intracellularly generated NO; much of the NO damaging activity occurred outside of the producer cells. Collectively, results presented in this study suggest that the type of cellular toxicity observed in macrophages is markedly influenced by rate of exposure to NO: at low rates of exposure, cells exhibit slower growth; at higher rates, cells begin to die; at even higher rates, cells undergo growth arrest or die. The ability of RAW264.7 cells to produce NO over many cell generations makes the cell line a useful system for the study of other aspects of cellular damage, including genotoxicity, resulting from exposure to NO under long-term conditions.

The role of nitric oxide as an effector of macrophage-mediated cytotoxicity against Trichomonas vaginalis

The purpose of this study is to determine whether nitric oxide is involved in the extracellular killing of Trichomonas vaginalis by mouse (BALB/c) peritoneal macrophages and RAW264.7 cells activated with LPS or rIFN-gamma and also to observe the effects of various chemicals which affect the production of reactive nitrogen intermediates (RNI) in the cytotoxicity against T. vaginalis. The cytotoxicity was measured by counting the release of [3H]-thymidine from labelled protozoa and NO2- was assayed by Griess reaction. NG-monomethyl-L-arginine (L-NMMA), NG-nitro-L-arginine methyl ester (NAME) and arginase inhibited cytotoxicity to T. vaginalis and nitrite production by activated mouse perioneal macrophages and RAW 264.7 cells. The addition of excess L-arginine competitively restored trichomonacidal activity of macrophages. Exogenous addition of FeSO4 inhibited cytotoxicity to T. vaginalis and nitric products of macrophages. From above results, it is assumed that nitric oxide plays an important role in the host defense mechanism of macrophages against T. vaginalis.

Induction of nitric oxide synthesis in J774 cells lowers intracellular glutathione: effect of modulated glutathione redox status on nitric oxide synthase induction

Under pathological conditions, the induction of nitric oxide synthase (NOS) in macrophages is responsible for NO production to a cytotoxic concentration. We have investigated changes to, and the role of, intracellular glutathione in NO production by the activated murine macrophage cell line J774. Total glutathione concentrations (reduced, GSH, plus the disulphide, GSSG) were decreased to 45% of the control 48 h after cells were activated with bacterial lipopolysaccharide plus interferon gamma. This was accompanied by a decrease in the GSH/GSSG ratio from 12:1 to 2:1. The intracellular decrease was not accounted for by either GSH or GSSG efflux; on the contrary, rapid export of glutathione in control cells was abrogated during activation. The loss of intra- and extracellular glutathione indicates either a decrease in synthesis de novo, or an increase in utilization, rather than competition for available NADPH. All changes in activated cells were prevented by pretreatment with the NOS inhibitor L-N-(1-iminoethyl)ornithine. Basal glutathione levels in J774 cells were manipulated by pretreatment with (1) buthionine sulphoximine (glutathione synthase inhibitor), (2) acivicin (gamma-glutamyltranspeptidase inhibitor), (3) bromo-octane (glutathione S-transferase substrate) and (4) diamide/zinc (thiol oxidant and glutathione reductase inhibitor). All treatments significantly decreased the output of NO following activation. The degree of inhibition was dependent on (i) duration of treatment prior to activation, (ii) rate of depletion or subsequent recovery and (iii) thiol end product. The level of GSH did not significantly affect the production of NO, after induction of NOS. Thus, glutathione redox status appears to plays an important role in NOS induction during macrophage activation.

In vivo expression of inducible nitric oxide synthase in supraventricular amoeboid microglial cells in neonatal BALB/c and athymic mice

The present study investigated whether the supraventricular amoeboid microglial cells (SAMC) in neonatal BALB/c and athymic nude mice were able to express inducible nitric oxide synthase (iNOS) after intraperitoneal injections of lipopolysaccharide (LPS) or interferon-gamma (IFN-gamma). The results showed that iNOS, undetectable in these cells in vehicle injected mice, could clearly be demonstrated immunohistochemically in a large number of them in LPS treated normal and mutant mice. Only a few iNOS-positive SAMC were observed in IFN-gamma injected mice. Immunoelectron microscopy confirmed the microglial nature of the labelled cells and that the immunoprecipitate of iNOS was cytosolic, being diffusely present throughout the cytoplasm of the cells. It is suggested that iNOS in the SAMC of neonatal BALB/c and athymic mice may be involved in the synthesis of nitric oxide which is necessitated more for host defence mechanism against bacterial endotoxin than against immunological stimuli.

The involvement of nitric oxide in the anti-Candida albicans activity of rat neutrophils

Rat peritoneal neutrophils (PMN) spontaneously release nitric oxide (NO) when incubated in vitro. Addition of the NO synthase inhibitor L-monomethylarginine (L-NMMA) to the PMN reduces NO production and impairs the killing of the yeast Candida albicans, both effects being reversed by L-arginine. These data strongly suggest that oxidative metabolism of L-arginine by PMN is involved in the candidacidal activity of these cells. Rat blood PMN, which do not produce significant amounts of NO, exhibit a reduced killing capacity compared with peritoneal cells, except when they are obtained from lipopolysaccharide (LPS)-treated rats. In this case they produce measurable amounts of nitrite and express high fungicidal activity in vitro. Confirming the candidacidal activity of NO, the exposure of the C. albicans cultures to different concentrations of NO donors leads to a reduction in their survival. The candidacidal activity related to the NO pathway in rat PMN is phagocytosis dependent, since the activity can be inhibited by cytochalasin B. However, the oxidative products of oxygen released by rat PMN do not seem to be involved in their candidacidal activity, as incubation of the cells with phorbol myristate acetate (PMA) increases release of superoxide anion but does not affect the pattern of killing. Our results suggest that NO could be an important candidacidal pathway in rat neutrophils.

IL-4-deficient Balb/c mice resist infection with Leishmania major

Mice with a genetically engineered deficiency for either IL-4 or IFN-gamma R1 (single mutants), and IL-4/IFN-gamma R1 (double mutants) on the Balb/c and 129Sv background were used to study the course of infection with Leishmania major. In contrast to genetically resistant 129Sv wildtype mice, IL-4/IFN-gamma R1 double mutant mice developed fetal disease with parasite dissemination to visceral organs similar to mice lacking IFN-gamma R1 only. Balb/c mice, which are exquisitely susceptible to L. major, were rendered resistant to infection by disruption of the IL-4 gene. As compared to homozygous IL-4+/- mice, heterozygous IL-4+/- mice, heterozygous IL-4+/- animals consistently developed smaller lesions with less ulceration and necrosis, indicating the likelihood of gene-dosage effects. This implicates that the magnitude of the IL-4 response determines the severity of disease. CD4+ T cells of IL-4-deficient mice showed impaired Th2 cell development, as assessed by quantitative RT-PCR of characteristic cytokines. Development of resistance is not explained by default Th1 development, because this was observed only at very late stages of infection. Moreover, the induction of inflammatory cytokines (e.g., IL-1 alpha, IL-1 beta, TNF-alpha, IL-12) together with iNOS in the lesion and draining lymph nodes was not altered in the absence of IL-4.

Blood, bone marrow and splenic lymphocyte subset profiles in Indian visceral leishmaniasis

We examined the lymphocyte subsets in peripheral blood, bone marrow and spleen of 11 patients with acute visceral leishmaniasis (VL) and 9 with chronic VL before and after 8 weeks of antileishmanial therapy. On admission, the CD4 cell count was depressed in the peripheral blood of acute and chronic VL cases as compared to the value in 10 normal control subjects. In contrast, CD4 cell counts were higher in the bone marrow in acute and chronic cases, and in splenic aspirates of chronic cases only, compared to normal values. The peripheral blood CD8 cell count, while normal in acute cases, was uniformly low in chronic cases. Counts of CD8 cells were also low in bone marrow of acute and chronic cases, as well as in splenic aspirates of chronic cases only. All these differences were significant (P < 0.05). After treatment, the CD4 cell count in the peripheral blood increased, but decreased in bone marrow and splenic aspirates. The CD8 cell count remained unaltered in the peripheral blood but increased significantly (P < 0.05) in bone marrow and spleen. The results suggest that in VL the peripheral blood picture may not reveal the actual T cell subset profile in the reticuloendothelial system. The changes in CD8 cell counts in the bone marrow and spleen seem to be independent, and are probably influenced by antileishmanial therapy.

Histochemical demonstration of nitric oxide synthase-like immunoreactivity in epiplexus cells and choroid epithelia in the lateral ventricles of postnatal rat brain induced by an intracerebral injection of lipopolysaccharide

The present in vivo study showed the expression of nitric oxide synthase-like immunoreactivity in epiplexus cells in the lateral ventricles induced by intracerebral injection of lipopolysaccharide into postnatal rats. Nitric oxide synthase-like immunoreactivity was vigorously expressed in epiplexus cells 1 and 3 days after the lipopolysaccharide injection, but by 7 days post-injection, it became undetectable. The expression of nitric oxide synthase-like immunoreactivity was also observed in some of the choroid epithelial cells. The nitric oxide synthase-like immunoreactivity in these cells appeared to be more intense in the ventricle ipsilateral to the LPS injection than that on the contralateral side. The immunostaining patterns of OX-42 and OX-6 for the detection of complement type 3 receptors and major histocompatibility complex class II antigens respectively paralleled that of anti-nitric oxide synthase, indicating that lipopolysaccharide-induced nitric oxide synthase-like immunoreactivity was primarily in epiplexus cells. Immunoelectron microscopy revealed that the nitric oxide synthase-like immunoprecipitate in epiplexus cells and choroid epithelial cells filled the entire cytoplasm and in some areas associated with the membranes of some of the organelles especially the mitochondria, suggesting that the enzyme is mainly cytosolic. It is speculated that nitric oxide synthase in these cells is involved in the synthesis of nitric oxide. The nitric oxide production, if any, through the enzymatic activity of nitric oxide synthase in epiplexus cells as well as the choroid epithelial cells may be involved in host defense against bacterial endotoxin in the ventricular system of postnatal rat brain.

Effect of nitric oxide donors on survival of conidia, germination and growth of Aspergillus fumigatus in vitro

The effect of nitric oxide (NO) donors on survival of conidia, germination and growth of the opportunistic pathogenic fungus Aspergillus fumigatus was investigated. Most efficient was sodium nitrite in an acidic milieu (pH 4.5). At a concentration of 5 mmol/L it killed all resting conidia in buffer within 16 h. S-Nitroso derivatives of thiols (cysteine, N-acetylcysteine and N-acetylpenicillamine) at the same concentration killed about 30-50% of spores within 24 h. The NO scavenger, oxyhemoglobin, abolished these effects. S-Nitrosoglutathione had no fungicidal effect and promoted germination. Sodium nitrite and S-nitroso-N-acetylcysteine inhibited germination of conidia in various media from concentration of 0.5 mmol/L and stopped it at concentrations of 1.4-2.9 mmol/L. In media with glucose and casein hydrolyzate or sodium nitrate as nitrogen source, growth inhibition by sodium nitrite (0.5-2 mmol/L) was only weak and mostly transient. In general, the used strain A. fumigatus seems to be less sensitive to nitric oxide donors than dimorphic pathogenic fungi. Thus, nitric oxide is probably not a major effector molecule in killing phagocytized elements of this fungus by host's immunocytes.

Expression of the gene for inducible nitric oxide synthase in experimental glomerulonephritis in the rat

Nitrite, a stable product of nitric oxide (NO), is synthesized in vitro by glomeruli in experimental glomerulonephritis. We have now studied the expression of the gene for inducible NO synthase (iNOS) in accelerated nephrotoxic nephritis (NTN). The purpose of the study was to confirm in vivo induction of iNOS in this model of immune complex disease, and to relate the onset of induction and the level of expression to pathogenic events in the model. Glomeruli from rats with NTN were isolated at 6 h, 24 h and 2, 4 and 7 days and total RNA extracted. RNA (10 micrograms) was reverse transcribed and polymerase chain reaction (PCR) was performed with primers homologous to rat vascular smooth muscle iNOS and rat beta actin. A 222-base PCR product corresponding to iNOS mRNA was present in all experimental animals. iNOS expression was also found in activated macrophages, neutrophils and IL-1-stimulated but not unstimulated mesangial cells. Quantitative competitive PCR was carried out on glomerular samples using a 514-bp mutant of a 735-bp PCR product. iNOS expression was present at low levels in normal glomeruli and was markedly enhanced at 6 h after the induction of glomerulonephritis and peaked at 24 h. Increased iNOS expression persisted to day 7. beta actin mRNA levels were similar in all glomerular specimens. This study demonstrates that there is in vivo induction of iNOS in immune complex glomerulonephritis, corresponding to the generation of nitrite we have previously reported. iNOS gene expression is detectable within 6 h of induction of NTN, indicating the onset of gene transcription is closely related to the initial formation of immune complexes.

CD23 and IgE expression during the human immune response to cutaneous leishmaniasis: possible role in monocyte activation

Leishmania brasiliensis causes cutaneous leishmaniasis (CL) in humans. During this infection, a variety of inflammatory mediators are produced by T cells and monocytes/macrophages. In the present study, we analysed serum IgE levels and their correlation with in situ expression of the low affinity receptor for IgE (Fc epsilon RII/CD23) in patients infected with L. brasiliensis before and following therapy. These analyses were compared to in situ expression of tumour necrosis factor-alpha (TNF alpha), interleukin 3 (IL3), interferon-gamma (IFN gamma) and IL4. Disease-free individuals from the same endemic area sensitized with L. brasiliensis antigens were also included in this work. Our data indicate that during infection, serum levels of IgE and TNF alpha increased and correlated with elevated in situ expression of CD23, IL4 and TNF alpha mRNA. This expression disappeared following successful treatment, but persisted in patients resistant to anti-leishmania therapy. Patients resistant to therapy differed from other cases by a dramatic decrease in their in vivo expression of IFN gamma protein. Analysis of CD23 function in purified human monocytes indicated that this antigen mediates IgE/anti-IgE-dependent TNF alpha production. These data suggest a possible in vivo role of CD23 in acute immune responses in human CL.