Sensitivity of bacteria to NaNO2 and to L-arginine-dependent system in murine macrophages

A tale of two sites: how inflammation can reshape the microbiomes of the gut and lungs

Inflammation can directly and indirectly modulate the bacterial composition of the microbiome. Although studies of inflammation primarily focus on its function to negatively select against potential pathogens, some bacterial species have the ability to exploit inflammatory byproducts for their benefit. Inflammatory cells release reactive nitrogen species as antimicrobial effectors against infection, but some facultative anaerobes can also utilize the increase in extracellular nitrate in their environment for anaerobic respiration and growth. This phenomenon has been studied in the gastrointestinal tract, where blooms of facultative anaerobic Gammaproteobacteria, primarily Escherichia coli, often occur during colonic inflammation. In cystic fibrosis, Pseudomonas aeruginosa, another Gammaproteobacteria facultative anaerobe, can reduce nitrogen for anaerobic respiration and it blooms in the airways of the chronically inflamed cystic fibrosis lung. This review focuses on the evidence that inflammation can provide terminal electron acceptors for anaerobic respiration and can support blooms of facultative anaerobes, such as E. coli and P. aeruginosa in distinct, but similar, environments of the inflamed gastrointestinal and respiratory tracts.

Effect of a Synthetic Immunomodulator on the Regulation of Gamma Interferon and Interleukin-10 Production during Salmonella Sepsis in Itys Mice

The present study examined the in vivo capacity of diHDA-glycerol, a new chemically defined compound that we synthesized, to enhance nonspecific resistance of Itys mice to a virulent Salmonella typhimurium challenge (>LD50). This compound derives from (E)-10 hydroxy-2 decenoic acid (10-HDA), a fatty acid isolated from Royal Jelly. Bacterial growth rate within the spleen, interferon-gamma (IFN-γ), interleukin-10 (IL-10), and nitric oxide (NO) levels were measured in splenocyte cultures from diHDA-glycerol-pretreated mice or saline infected controls, at various time intervals after infectious challenge. Repeated administration of diHDA-glycerol before bacterial inoculation resulted in increased bacterial clearance from the spleen, starting in the second week of infection, whereas in control mice, bacterial proliferation led to death beyond day 13 after challenge. In addition, spleen cells from infected mice produced elevated levels of IFN-γ but failed to produce IL-10. In contrast, on the second week post challenge, the time course of cytokine responses was modified by the pretreatment. Spleen cells from diHDA-glycerol pretreated mice exhibited significantly lower levels of IFN-γ and significantlty higher levels of the anti-inflammatory cytokine IL-10, when compared with those in infected controls. Furthermore, on the second week post challenge, the restored functional capacity of splenocytes to produce nitric oxide (NO) was apparently linked with diHDA-glycerol pretreatment. These results suggest that diHDA-glycerol accelerates some macrophage functions resulting in a more adequate modulation of the balance of inflammatory mediators and consequently, in an enhanced host defense against Salmonella infection.

Macrophage Cell Death Due toSalmonella entericaSerovar Typhi and Its Acid Stress Protein Has Features of Apoptosis

Salmonella spp. have been shown to cause apoptosis of various host cell types as a part of their infection process. However, the induction of apoptosis remains to be looked into under the different host environments including acidic stress experienced by the pathogen. In order to simulate the in vivo acidic conditions, we studied the potential of S. typhi and its protein expressed under in vitro acidic conditions to induce apoptosis in macrophages. Murine macrophages were isolated and interacted with serovar Typhi and its acid stress protein for different time periods. The assessment of nucleosomal DNA, and nuclear staining with H-33342 dye and flow cytometry indicated the occurrence of characteristic features of apoptosis. Analysis of data revealed that S. typhi caused apoptotic cell death in 61% of macrophages whereas stress-induced protein alone accounted for apoptotic cell death in 45% of macrophages. The present study, for the first time demonstrates the potential of stress-induced outermembrane component of S. typhi to induce apoptosis. Identification of such factors may offer new insights for understanding the pathophysiology of the disease during the host-pathogen interactions.

Unsaturated fatty acids as modulators of macrophage respiratory burst in the immune response against Rhodococcus equi and Pseudomonas aeruginosa

In this paper, using the monocyte/macrophage cell line RAW264.7, we systematically investigate the impact of macrophage enrichment with unsaturated fatty acids on cellular radical synthesis. We found that the intracellular production of reactive nitrogen and oxygen intermediates depends on the activation status of the macrophages. For unstimulated macrophages PUFA enrichment resulted in an increase in cellular radical synthesis. For stimulated macrophages, instead, an impeding action of unsaturated fatty acids on the respiratory burst could be seen. Of particular importance, the impact of unsaturated fatty acids on the macrophage respiratory burst was also observed in RAW264.7 cells cocultivated with viable bacteria of the species Rhodococcus equi or Pseudomonas aeruginosa. PUFA supplementation of macrophages in the presence of R. equi or P. aeruginosa reduced the pathogen-stimulated synthesis of reactive nitrogen and oxygen intermediates. Furthermore, the unsaturated fatty acids were found to impede the expression of the myeloperoxidase gene and to reduce the activity of the enzyme. Hence, our data provide indications of a possible value of PUFA application to people suffering from chronic infections with R. equi and P. aeruginosa as a concomitant treatment to attenuate an excessive respiratory burst.

Inactivation of the potent Pseudomonas aeruginosa cytotoxin pyocyanin by airway peroxidases and nitrite

Pyocyanin (1-hydroxy-N-methylphenazine, PCN) is a cytotoxic pigment and virulence factor secreted by the human bacterial pathogen, Pseudomonas aeruginosa. Here, we report that exposure of PCN to airway peroxidases, hydrogen peroxide (H(2)O(2)), and NaNO(2) generates unique mononitrated PCN metabolites (N-PCN) as revealed by HPLC/mass spectrometry analyses. N-PCN, in contrast to PCN, was devoid of antibiotic activity and failed to kill Escherichia coli and Staphylococcus aureus. Furthermore, in contrast to PCN, intratracheal instillation of N-PCN into murine lungs failed to induce a significant inflammatory response. Surprisingly, at a pH of ∼7, N-PCN was more reactive than PCN with respect to NADH oxidation but resulted in a similar magnitude of superoxide production as detected by electron paramagnetic resonance and spin trapping experiments. When incubated with Escherichia coli or lung A549 cells, PCN and N-PCN both led to superoxide formation, but lesser amounts were detected with N-PCN. Our results demonstrate that PCN that has been nitrated by peroxidase/H(2)O(2)/NO(2)(-) systems possesses less cytotoxic/proinflammatory activity than native PCN. Yield of N-PCN was decreased by the presence of the competing physiological peroxidase substrates (thiocyonate) SCN(-) (myeloperoxidase, MPO, and lactoperoxidase, LPO) and Cl(-) (MPO), which with Cl(-) yielded chlorinated PCNs. These reaction products also showed decreased proinflammatory ability when instilled into the lungs of mice. These observations add important insights into the complexity of the pathogenesis of lung injury associated with Pseudomonas aeruginosa infections and provide additional rationale for exploring the efficacy of NO(2)(-) in the therapy of chronic Pseudomonas aeruginosa airway infection in cystic fibrosis.

Analysis of nitric oxide-dependent antimicrobial actions in macrophages and mice

Nitric oxide (NO*) is a critical component of mammalian host defense that is produced in macrophages and other cells comprising the innate immune system. Isolated mammalian macrophages have been utilized to measure the kinetics of NO production and to demonstrate NO-related antimicrobial actions. Some microorganisms possess enzymes to detoxify nitrogen oxides, and mutant strains lacking these enzymes can be used to demonstrate the importance of these mechanisms for intracellular bacterial survival. This chapter describes techniques with which to analyze the antimicrobial actions of nitric oxide in murine and human macrophages and in laboratory mice.

N(2)O(3) enhances the nitrosative potential of IFNgamma-primed macrophages in response to Salmonella

We show here that the nitric oxide (NO)-detoxifying Hmp flavohemoprotein increases by 3-fold the transcription of the Salmonella pathogenicity island 2 (SPI2) in macrophages expressing a functional inducible NO synthase (iNOS). However, Hmp does not prevent NO-related repression of SPI2 transcription in IFNgamma-primed phagocytes, despite preserving intracellular transcription of sdhA sdhB subunits of Salmonella succinate dehydrogenase within both control and IFNgamma-primed phagocytes. To shed light into the seemingly paradoxical role that Hmp plays in protecting intracellular SPI2 expression in various populations of macrophages, N(2)O(3) was quantified as an indicator of the nitrosative potential of Salmonella-infected phagocytes in different states of activation. Hmp was found to prevent the formation of 300nM N(2)O(3)/h/bacteria in IFNgamma-primed macrophages, accounting for about a 60% reduction of the nitrosative power of activated phagocytes. Utilization of the vacuolar ATPase inhibitor bafilomycin indicates that a fourth of the approximately 200nM N(2)O(3)/h sustained by IFNgamma-primed macrophages is generated in endosomal compartments via condensation of HNO(2). In sharp contrast, control macrophages infected with wild-type Salmonella produce as little N(2)O(3) as iNOS-deficient controls. Collectively, these findings indicate that the NO-metabolizing activity of Salmonella Hmp is functional in both control and IFNgamma-primed macrophages. Nonetheless, a substantial amount of the NO generated by IFNgamma-primed macrophages gives rise to N(2)O(3), a species that not only enhances the nitrosative potential of activated phagocytes but also avoids detoxification by Salmonella Hmp.

55 kDa outer-membrane protein from short-chain fatty acids exposed Salmonella enterica serovar Typhi induces apoptosis in macrophages

Various pathogens including Salmonella species are known to induce apoptosis in host cell types during their infection processes. However, the bacterial components capable of inducing apoptosis have not been fully understood. It is now known that in vivo expression of virulence determinants differ from the expression under in vitro conditions. Therefore, in the present study, attempts were made to evaluate the apoptotic potential of outer-membrane protein (OMP) from short-chain fatty acids (SCFA) exposed Salmonella enterica serovar Typhi. Short-chain fatty acids exposure is one of the in vivo stresses encountered by the pathogen in the intestine. Therefore, to simulate the in vivo condition, S. enterica serovar Typhi was grown in the presence of SCFA and its OMP profile was analyzed. The apoptotic potential of 55 kDa protein expressed with enhanced intensity under the SCFA stress was evaluated. Murine peritoneal macrophages interacted with 55 kDa protein showed DNA fragmentation, changes in fluorescence and exposure of phosphatidylserine on their outer leaflets. Levels of nitrite and citrulline were found to be increased in the supernatant of macrophages after interacting them with 55 kDa protein. However, the enzymatic activity of superoxide dismutase was found to be decreased as compared to that of the control (uninteracted) macrophages. These observations indicate that increased levels of nitrite and decreased levels of superoxide dismutase may be one of the mechanisms to induce apoptosis in macrophages by SCFA induced 55 kDa OMP. These findings may help us better understand the pathophysiology of the disease during the host pathogen interactions.

Nitric Oxide in Salmonella and Escherichia coli Infections

This review discusses the role that nitric oxide (NO) and its congeners play on various stages in the pathophysiology of Escherichia coli and Salmonella infections, with special emphasis on the regulatory pathways that lead to high NO synthesis, the role of reactive nitrogen species (RNS) in host resistance, and the bacterial molecular targets and defense mechanisms that protect enteric bacteria against the nitrosative stress encountered in diverse host anatomical sites. In general, NO can react directly with prosthetic groups containing transition metal centers, with other radicals, or with sulfhydryl groups in the presence of an electron acceptor. Binding to iron complexes is probably the best characterized direct reaction of NO in biological systems. The targets of RNS are numerous. RNS can facilitate oxidative modifications including lipid peroxidation, hydroxylation, and DNA base and protein oxidation. In addition, RNS can inflict nitrosative stress through the nitrosation of amines and sulfhydryls. Numerous vital bacterial molecules can be targeted by NO. It is therefore not surprising that enteropathogenic bacteria are armed with a number of sensors to coordinate the protective response to nitrosative stress, along with an assortment of antinitrosative defenses that detoxify, repair, or avoid the deleterious effects of RNS encountered within the host. NO and NO-derived RNS play important roles in innate immunity to Salmonella and E. coli. Enzymatic NO production by NO synthases can be enhanced by microbial and other inflammatory stimuli and it exerts direct antimicrobial actions as well as immunomodulatory and vasoregulatory effects.

Effects of Brazilian and Bulgarian propolis on bactericidal activity of macrophages against Salmonella Typhimurium

Propolis has been used in folk medicine since ancient times due to its many biological properties, such as antimicrobial, antiinflammatory, antioxidant, immunomodulatory activities, among others. Macrophages play an important role in the early phase of Salmonella infection. In this work, macrophages were prestimulated with Brazilian or Bulgarian propolis and subsequently challenged with Salmonella Typhimurium at different macrophage/bacteria ratio. After 60 min of incubation, cells were harvested with Triton-X to lyse the macrophages. To assess the bactericidal activity, the number of colony-forming units (CFU) of S. typhimurium was determined by plating 0.1 mL in Mueller Hinton agar. After 24 h, CFU were counted, and the percentage of bactericidal activity was obtained. Propolis from Brazil and Bulgaria enhanced the bactericidal activity of macrophages, depending on its concentration. Brazilian propolis seemed to be more efficient than that from Bulgaria, because of their different chemical composition. In Bulgaria, bees collect the material mainly from the bud exudate of poplar trees, while in Brazil, Baccharis dracunculifolia DC. was shown to be the main propolis source. Our data also showed that the increased bactericidal activity of macrophages involved the participation of oxygen (H(2)O(2)) and nitrogen (NO) intermediate metabolites.

Assessment of safety of lactobacillus strains based on resistance to host innate defense mechanisms

Seven Lactobacillus strains belonging to four species were evaluated for pathogenicity as well as for in vitro sensitivity to the bactericidal mechanisms of macrophages in a rabbit infective endocarditis (IE) model. Two bacteremia-associated strains, L. rhamnosus PHLS A103/70 and L. casei PHLS A357/84, as well as the L. rhamnosus type strain and the probiotic L. rhamnosus strain ATCC 53103, showed moderate infectivity, and the virulence of the probiotic L. casei strain Shirota and type strains such as L. acidophilus ATCC 4356(T) and L. gasseri DSM 20243(T) in the model was negligible. The strains that showed pathogenic potential in the rabbit IE model (PHLS A357/84, PHLS A103/70, and ATCC 53103) were more resistant than strain Shirota to intracellular killing activity by mouse macrophages in vitro and also to bactericidal nitrogen intermediates, such as nitric oxide and NO(2)(-) ions. These results suggest that resistance to host innate defense systems, which would function at inflammatory lesions, should be considered in the safety assessment of Lactobacillus strains.

Implications of Salmonella-induced nitric oxide (NO) for host defense and vaccines: NO, an antimicrobial, antitumor, immunosuppressive and immunoregulatory molecule

Attenuated Salmonella induce immunosuppressive, microbicidal and tumoricidal macrophages in mice. All three effects are mediated by activated macrophages producing nitric oxide (NO). NO is induced by the innate immune response pathway involving IL-12, NK cells and IFN-gamma in response to infection. NO has beneficial and detrimental effects on the host.

Nitric oxide production and iNOS mRNA expression in mice induced by repeated stimulation with live Fusobacterium nucleatum

There have been few studies on the detection of direct nitric oxide (NO) production and interferon-gamma (IFN-gamma) in vivo without using animal cell culture. We questioned whether NO and IFN-gamma could be produced at the site of infection. The peritoneal cavity of mice was used as the local infection model. NO and IFN-gamma in abdominal washings from these mice were measured directly at various times after injection of Fusobacterium nucleatum, a gram-negative rod periodontal pathogen. The mice were divided into three groups: those treated with live bacteria (LB), those treated with heat-killed bacteria (HKB) and those untreated: normal (N). These mice were compared on the basis of cell filtration, NO and IFN-gamma production by injection of live bacteria (LFn) or heat-killed bacteria (HKFn). In the LB group, the total cell number increased corresponding to an increase in neutrophils after injection of both LFn and HKFn. A low level of NO was constantly produced in abdominal washings, but a significant amount of NO was synthesized in the LB group only 12 hr to 24 hr after injection of LFn. At the same time iNOS enzyme activity and iNOS mRNA expression were detected. IFN-gamma, which may contribute to enhance NO production, was also secreted at a high level from peritoneal exudate cells (PEC) at 12 hr and 24 hr in the LB group by stimulation of LFn. At 12 hr and 24 hr, iNOS positive cells in the LB group by infection of LFn were identified and shown to contain mostly macrophages. These findings indicate that live bacteria play important roles in NO production by macrophages. It is suggested that NO may contribute to the inflammatory response during F. nucleatum infection in periodontitis.

Inducible nitric oxide synthase and Salmonella infection

Salmonella infection is associated with the increased expression of inducible nitric oxide synthase in macrophages and other cells. This review summarizes current knowledge of the molecular mechanisms involved in the induction process, and discusses the functional significance of nitric oxide production in the context of host defense against Salmonella.

Oxygen-dependent anti-Salmonella activity of macrophages

Numerous observations have established a crucial role for phagocytic cells in host resistance to Salmonella. Activated macrophages rely on a complex array of oxygen-dependent antimicrobial molecules to inhibit or kill intracellular Salmonella. An initial oxidative bactericidal phase, which is dependent on the respiratory burst phagocyte oxidase (phox) is succeeded by a prolonged nitrosative bacteriostatic phase, which is dependent on inducible nitric oxide synthase (iNOS). The sequential contribution of phox and iNOS to anti-Salmonella innate immunity has been demonstrated both in vitro and in vivo. The temporal progression from the predominant production of reactive oxygen species to the production of nitrogen oxides could optimize the initial reduction in microbial burden while minimizing the immunopathological consequences of the host inflammatory response.

Nitric oxide metabolites in gnotobiotic piglets orally infected with Salmonella enterica serovar typhimurium

Reactive NO metabolites play a distinct role in the control of Salmonella enterica serovar Typhimurium (ST; a facultative intracellular pathogen) in susceptible host. A significant increase of nitrite and/or nitrate plasma levels, 3-nitro-tyrosine expression and pathological changes in mesenteric lymph nodes have been observed in gnotobiotic piglets orally infected for 1 d with a virulent strain of ST but not in piglets infected with a rough mutant of ST.

Antimicrobial actions of the NADPH phagocyte oxidase and inducible nitric oxide synthase in experimental salmonellosis. I. Effects on microbial killing by activated peritoneal macrophages in vitro

The contribution of the NADPH phagocyte oxidase (phox) and inducible nitric oxide (NO) synthase (iNOS) to the antimicrobial activity of macrophages for Salmonella typhimurium was studied by using peritoneal phagocytes from C57BL/6, congenic gp91phox(-/)-, iNOS(-/)-, and doubly immunodeficient phox(-/)-iNOS(-/)- mice. The respiratory burst and NO radical (NO.) made distinct contributions to the anti-Salmonella activity of macrophages. NADPH oxidase-dependent killing is confined to the first few hours after phagocytosis, whereas iNOS contributes to both early and late phases of antibacterial activity. NO-derived species initially synergize with oxyradicals to kill S. typhimurium, and subsequently exert prolonged oxidase-independent bacteriostatic effects. Biochemical analyses show that early killing of Salmonella by macrophages coincides with an oxidative chemistry characterized by superoxide anion (O(2).(-)), hydrogen peroxide (H(2)O(2)), and peroxynitrite (ONOO(-)) production. However, immunofluorescence microscopy and killing assays using the scavenger uric acid suggest that peroxynitrite is not responsible for macrophage killing of wild-type S. typhimurium. Rapid oxidative bacterial killing is followed by a sustained period of nitrosative chemistry that limits bacterial growth. Interferon gamma appears to augment antibacterial activity predominantly by enhancing NO. production, although a small iNOS-independent effect was also observed. These findings demonstrate that macrophages kill Salmonella in a dynamic process that changes over time and requires the generation of both reactive oxidative and nitrosative species.

In vivo blockage of nitric oxide with aminoguanidine inhibits immunosuppression induced by an attenuated strain of Salmonella typhimurium, potentiates Salmonella infection, and inhibits macrophage and polymorphonuclear leukocyte influx into the spleen

Our laboratory has previously shown that after immunization with a strain of Salmonella typhimurium, SL3235, made avirulent by a blockage in the pathway of aromatic synthesis, murine splenocytes were profoundly suppressed in their capacity to mount an in vitro antibody plaque-forming cell (PFC) response to sheep erythrocytes. Evidence indicated that suppression was mediated by nitric oxide (NO), since the in vitro addition of NG-monomethyl-L-arginine blocked suppression. The present studies examined the effect of blocking NO production on Salmonella-induced immunosuppression by in vivo administration of aminoguanidine hemisulfate (AG). AG was administered to C3HeB/FeJ mice in their drinking water (2.5% solution) for 7 days prior to intraperitoneal inoculation with SL3235. AG treatment inhibited the increase in nitrate and nitrite levels in plasma and nitrite levels in the spleen seen in immunized mice. Importantly, AG treatment completely blocked suppression of the splenic PFC response and markedly attenuated the suppression of the response to concanavalin A in immunized mice, providing further evidence that Salmonella-induced immunosuppression is mediated by NO. AG treatment also alleviated the majority of the splenomegaly associated with SL3235 inoculation, which correlated with a blockage of influx of neutrophils and macrophages into spleens, as assessed by flow cytometry. AG treatment unexpectedly resulted in 90% mortality in mice injected with the highly attenuated vaccine strain of Salmonella, SL3235. Increased mortality in AG-treated mice correlated with inability to clear organisms from the spleen by day 15 postinoculation and with persistent bacteremia, compared with control mice. Collectively, these in vivo results underscore the dual biological consequences of NO production following Salmonella infection, with NO being necessary for host defense, but also having the potentially adverse effect of immunosuppression. A unifying hypothesis to explain how these seemingly paradoxical effects could both result from NO production is presented.

Inducible nitric oxide synthase expression is reduced in cystic fibrosis murine and human airway epithelial cells

It has been reported that exhaled nitric oxide levels are reduced in cystic fibrosis (CF) patients. We have examined the inducible isoform of nitric oxide synthase (iNOS) in the airways by immunostaining and found that iNOS is constitutively expressed in the airway epithelia of non-CF mouse and human tissues but essentially absent in the epithelium of CF airways. We explored potential consequences of lost iNOS expression and found that iNOS inhibition significantly increases mouse nasal trans-epithelial potential difference, and hindered the ability of excised mouse lungs to prevent growth of Pseudomonas aeruginosa. The absence of continuous nitric oxide production in epithelial cells of CF airways may play a role in two CF-associated characteristics: hyperabsorption of sodium and susceptibility to bacterial infections.

Erratic behavior of nitric oxide within the immune system: illustrative review of conflicting data and their immunopharmacological aspects

The literature data assembled in this article document the variation of immunobiological effects of nitric oxide (NO). A number of factors are obviously responsible for the diversity, ranging from inactivity, alleviation, but not rarely to exacerbation of certain pathogenetic processes. A better understanding of NO interactions with the immune system can only be reached if more complex experimental designs to study the effects of reactive nitrogen species are adopted in the future. They should integrate major participating variables and take into account pharmacodynamic/kinetic aspects of NO production in triggering the ultimate effects. If manipulation of NO in the organism by means of recently developed NO inhibitors and NO donors is to become a rational tool of immunopharmacological strategies, detailed knowledge of their pharmacologies and toxicologies is urgently needed in order to differentiate between the effects of NO and other side effects. Hopefully, this approach could improve the predictability of the clinical outcomes of NO manipulation.

A seroepidemiologic survey on brucellosis antibodies in southern Italy

This study investigated the prevalence of Brucella antibodies in the general population in two regions in southern Italy. A total of 1,294 subjects were recruited from January to June 1996 among patients attending randomly selected public and private laboratories and pediatric outpatient clinics. Information on sex, age, residence, and occupation was recorded. Seroprevalence of brucellosis was studied by the safranin O-stained antigen microagglutination test. The chi-square test and multiple logistic regression were performed. An overall prevalence of brucellosis of 3.1% was recorded; no significant difference was found between the two regions, with values of 2.7% in Campania and 3.8% in Calabria. Multiple logistic regression analysis indicated that positivity to brucellosis was significantly associated with the province the subjects reside in, ranging from 0 in Salerno to 6.2% in Caserta, and that it significantly increased with age, ranging from 1% in persons under 16 to 4.2% in those over 65 (OR = 1.7; 95% CI = 1.04-2.6), whereas it was not significantly associated with sex. When analysis was conducted after restriction to subjects reporting to be working, occupation was found not to be significantly associated with brucellosis. Since the spread of the disease is still of concern, though circulation of Brucella is decreasing, strict application of measures for the eradication of brucellosis from livestock, pasteurization of milk and dairy products, and education regarding eating habits must be pursued.

Nitric oxide in sepsis

The synthesis of nitric oxide (NO) and its targets are reviewed physiologically during sepsis and wound healing, a self-limiting process in which mechanisms are still identified incompletely. NO also plays an active and direct role during infection, aimed at protecting the host and destroying the microbe. During septic shock, an overproduction of NO has been described experimentally and clinically that might be responsible for the systemic vasodilatation with hyporesponsiveness to exogenous vasoconstrictive agents. The different manipulations of NO pathway during sepsis are described (transcription and post-transcription of iNOS, enzymatic function, substrate availability, NO concentration, and NO effector molecules), although their clinical benefit remains controversial.

Effect of nitric oxide on staphylococcal killing and interactive effect with superoxide

The role of reactive nitrogen intermediates (RNI) such as nitric oxide (.NO) in host defense against pyogenic microorganisms is unclear, and the actual interactive effect of RNI and reactive oxidative intermediates (ROI) for microbial killing has not been determined. Since, in nature, ROI and RNI might be generated together within any local infection, we evaluated the separate and interactive effects of .NO and O2- on staphylococcal survival by using a simplified system devoid of eukaryotic cells. These studies showed that prolonged exposure of staphylococci to .NO does not result in early loss of viability but instead is associated with a dose-related delayed loss of viability. This effect is abrogated by the presence of hemoglobin, providing further evidence that the effect is RNI associated. Superoxide-mediated killing also is dose related, but in contrast to RNI-mediated killing, it is rapid and occurs within 2 h of exposure. We further show that the interaction of .NO and O(2)- results in decreased O(2)--mediated staphylococcal killing at early time points. .NO, however, appears to enhance or stabilize microbial killing over prolonged periods of incubation. This study did not produce evidence of early synergism of ROI and RNI, but it does suggest that .NO may contribute to host defense, especially when ROI-mediated killing is compromised.

Production of reactive nitrogen intermediates (RNI) by peritoneal macrophages from rats with experimental autoimmune prostatitis (EAP)

Peritoneal macrophages from experimental autoimmune prostatitis (EAP) rats were examined for their capacity to secrete reactive nitrogen intermediates (RNI), measured by the release of nitrite (NO2-). Under basal conditions, there was a significant increase of NO2- secretion by cells from autoimmune rats in relation to resident cells. After stimulation in vitro with lipopolysaccharide (LPS), the NO2- production was higher in cells from autoimmune rats compared to treated and nontreated controls. The NO2- production was dependent upon the presence of L-arginine in the culture medium. The addition of L-NG-monomethyl arginine, an inhibitor of nitric oxide synthesis, to the medium reduced the amount of measurable NO2-. Kinetic studies in cells from EAP rats showed that in basal conditions there was an significant release of NO2- at day 7 of immunization that was maintained during the whole period studied. After LPS stimulation, there was a similar behavior and maximum values were reached at day 28 of immunization. These results, together with the lesion observed in the prostate gland, suggest that RNI may be of pathogenic importance in the development of early tissue inflammation and autoimmune disease of the prostate.

Staphylococcal glycocalyx activates macrophage prostaglandin E2 and interleukin 1 production and modulates tumor necrosis factor alpha and nitric oxide production

We have examined the effect of staphylococcal glycocalyces on the ability of murine peritoneal macrophages to produce prostaglandin E2 (PGE2) and the inflammatory cytokines interleukin 1 (IL-1) and tumor necrosis factor alpha (TNF-alpha) and to generate nitric oxide. Glycocalyx partially purified under endotoxin-free conditions from defined liquid medium cultures of Staphylococcus lugdunensis or Staphylococcus epidermidis was a strong stimulator of PGE2 and IL-1 production. The addition of 10 to 100 micrograms of glycocalyx per ml induced levels of IL-1 and PGE2 production similar to that induced by 0.1 to 1 micrograms of Escherichia coli lipopolysaccharide (LPS) per ml. In contrast, glycocalyx induced ninefold less TNF-alpha and three- to fourfold less nitrite than LPS. A modulatory effect was suggested by the observation that the amount of TNF-alpha and nitrite generated remained constant whether the macrophages were stimulated with 10 or 100 micrograms of glycocalyx per ml. A selective modulation of macrophage activation was confirmed by the demonstration that costimulation of macrophages with both glycocalyx and LPS resulted in a reduction in TNF-alpha and nitrite generation relative to stimulation with LPS alone even though costimulation had no effect on PGE2 production and increased IL-1 production. Involvement of PGE2 in this modulatory effect was suggested by the ability of indomethacin to augment glycocalyx-stimulated TNF-alpha production and to reverse the inhibitory effect of glycocalyx on LPS induction of TNF-alpha production. However, the inability of indomethacin to reverse the inhibitory effect of glycocalyx on LPS-induced nitric oxide generation suggests that the selective modulation of macrophage function by glycocalyx may be more complex than increased sensitivity to PGE2 feedback inhibition.

Inhibition of Legionella pneumophila growth by gamma interferon in permissive A/J mouse macrophages: role of reactive oxygen species, nitric oxide, tryptophan, and iron(III)

A/J mouse macrophages infected with Legionella pneumophila and treated with gamma interferon (IFN-gamma) in vitro developed potent antimicrobial activity. This antilegionella activity was independent of the macrophage capacity to generate reactive oxygen intermediates, since the oxygen radical scavengers catalase, superoxide dismutase, mannitol, and thiourea had no effect on the antilegionella activity of IFN-gamma-activated macrophages. Likewise, whereas the ability of IFN-gamma-activated macrophages to synthesize reactive nitrogen intermediates was markedly inhibited by the L-arginine (Arg) analogs, NG-monomethyl-L-arginine and L-aminoguanidine, as well as by incubation in L-Arg-free medium, their ability to inhibit the intracellular growth of L. pneumophila remained intact. The intracellular growth of L. pneumophila in A/J macrophages was inhibited by the iron(III) chelator desferrioxamine and reversed by Fe-transferrin as well as by ferric salts. Additionally, IFN-gamma-activated macrophages incorporated 28% less 59Fe(III) compared with nonactivated cells. Nonetheless, only partial blocking of growth restriction was observed when IFN-gamma-stimulated macrophages were saturated with iron(III). Indole-propionic acid, which appears to inhibit the biosynthesis of L-tryptophan (L-Trp), was an L-Trp-reversible growth inhibitor of L. pneumophila in macrophages, implying that the intracellular replication of this pathogen is also L-Trp dependent. However, an excess of exogenous L-Trp did not reverse the growth inhibition due to IFN-gamma, though a small synergistic effect was observed when the culture medium was supplemented with both iron(III) and L-Trp. We conclude that IFN-gamma-activated macrophages inhibit the intracellular proliferation of L. pneumophila by reactive oxygen intermediate- and reactive nitrogen intermediate-independent mechanisms and just partially by nutritionally dependent mechanisms. We also suggest that additional mechanisms, still unclear, may be involved, since complete reversion was never obtained and since at higher concentrations of IFN-gamma, iron(III) did not induce any significant reversion in the L. pneumophila growth inhibition.

Effect of pyocyanine, a pigment of Pseudomonas aeruginosa, on production of reactive nitrogen intermediates by murine alveolar macrophages

In this study we investigated the effect of pyocyanine, a pigment produced by Pseudomonas aeruginosa, on production of reactive nitrogen intermediates by macrophages. We found that addition of pyocyanine to cultures of murine alveolar macrophages inhibited the capacity of these cells to produce reactive nitrogen intermediates (measured as nitrite) in a dose-dependent manner without altering cell viability, cytokine-induced Ia expression, or production of tumor necrosis factor.