Immune dysfunction in endotoxicosis: Role of nitric oxide produced by inducible nitric oxide synthase*

Sevoflurane Promotes Bactericidal Properties of Macrophages through Enhanced Inducible Nitric Oxide Synthase Expression in Male Mice

BACKGROUND

Sevoflurane with its antiinflammatory properties has shown to decrease mortality in animal models of sepsis. However, the underlying mechanism of its beneficial effect in this inflammatory scenario remains poorly understood. Macrophages play an important role in the early stage of sepsis as they are tasked with eliminating invading microbes and also attracting other immune cells by the release of proinflammatory cytokines such as interleukin-1β, interleukin-6, and tumor necrosis factor-α. Thus, the authors hypothesized that sevoflurane mitigates the proinflammatory response of macrophages, while maintaining their bactericidal properties.

METHODS

Murine bone marrow-derived macrophages were stimulated in vitro with lipopolysaccharide in the presence and absence of 2% sevoflurane. Expression of cytokines and inducible NO synthase as well as uptake of fluorescently labeled Escherichia coli (E. coli) were measured. The in vivo endotoxemia model consisted of an intraperitoneal lipopolysaccharide injection after anesthesia with either ketamine and xylazine or 4% sevoflurane. Male mice (n = 6 per group) were observed for a total of 20 h. During the last 30 min fluorescently labeled E. coli were intraperitoneally injected. Peritoneal cells were extracted by peritoneal lavage and inducible NO synthase expression as well as E. coli uptake by peritoneal macrophages was determined using flow cytometry.

RESULTS

In vitro, sevoflurane enhanced lipopolysaccharide-induced inducible NO synthase expression after 8 h by 466% and increased macrophage uptake of fluorescently labeled E. coli by 70% compared with vehicle-treated controls. Inhibiting inducible NO synthase expression pharmacologically abolished this increase in bacteria uptake. In vivo, inducible NO synthase expression was increased by 669% and phagocytosis of E. coli by 49% compared with the control group.

CONCLUSIONS

Sevoflurane enhances phagocytosis of bacteria by lipopolysaccharide-challenged macrophages in vitro and in vivo via an inducible NO synthase-dependent mechanism. Thus, sevoflurane potentiates bactericidal and antiinflammatory host-defense mechanisms in endotoxemia.

NOS1-derived nitric oxide promotes NF-κB transcriptional activity through inhibition of suppressor of cytokine signaling-1

The NF-κB pathway is central to the regulation of inflammation. Here, we demonstrate that the low-output nitric oxide (NO) synthase 1 (NOS1 or nNOS) plays a critical role in the inflammatory response by promoting the activity of NF-κB. Specifically, NOS1-derived NO production in macrophages leads to proteolysis of suppressor of cytokine signaling 1 (SOCS1), alleviating its repression of NF-κB transcriptional activity. As a result, NOS1(-/-) mice demonstrate reduced cytokine production, lung injury, and mortality when subjected to two different models of sepsis. Isolated NOS1(-/-) macrophages demonstrate similar defects in proinflammatory transcription on challenge with Gram-negative bacterial LPS. Consistently, we found that activated NOS1(-/-) macrophages contain increased SOCS1 protein and decreased levels of p65 protein compared with wild-type cells. NOS1-dependent S-nitrosation of SOCS1 impairs its binding to p65 and targets SOCS1 for proteolysis. Treatment of NOS1(-/-) cells with exogenous NO rescues both SOCS1 degradation and stabilization of p65 protein. Point mutation analysis demonstrated that both Cys147 and Cys179 on SOCS1 are required for its NO-dependent degradation. These findings demonstrate a fundamental role for NOS1-derived NO in regulating TLR4-mediated inflammatory gene transcription, as well as the intensity and duration of the resulting host immune response.

Global sensitivity analysis of a mathematical model of acute inflammation identifies nonlinear dependence of cumulative tissue damage on host interleukin-6 responses

The precise inflammatory role of the cytokine interleukin (IL)-6 and its utility as a biomarker or therapeutic target have been the source of much debate, presumably due to the complex pro- and anti-inflammatory effects of this cytokine. We previously developed a nonlinear ordinary differential equation (ODE) model to explain the dynamics of endotoxin (lipopolysaccharide; LPS)-induced acute inflammation and associated whole-animal damage/dysfunction (a proxy for the health of the organism), along with the inflammatory mediators tumor necrosis factor (TNF)-α, IL-6, IL-10, and nitric oxide (NO). The model was partially calibrated using data from endotoxemic C57Bl/6 mice. Herein, we investigated the sensitivity of the area under the damage curve (AUCD) to the 51 rate parameters of the ODE model for different levels of simulated LPS challenges using a global sensitivity approach called Random Sampling High Dimensional Model Representation (RS-HDMR). We explored sufficient parametric Monte Carlo samples to generate the variance-based Sobol' global sensitivity indices, and found that inflammatory damage was highly sensitive to the parameters affecting the activity of IL-6 during the different stages of acute inflammation. The AUCIL6 showed a bimodal distribution, with the lower peak representing healthy response and the higher peak representing sustained inflammation. Damage was minimal at low AUCIL6, giving rise to a healthy response. In contrast, intermediate levels of AUCIL6 resulted in high damage, and this was due to the insufficiency of damage recovery driven by anti-inflammatory responses from IL-10 and the activation of positive feedback sustained by IL-6. At high AUCIL6, damage recovery was interestingly restored in some population of simulated animals due to the NO-mediated anti-inflammatory responses. These observations suggest that the host's health status during acute inflammation depends in a nonlinear fashion on the magnitude of the inflammatory stimulus, on the host's propensity to produce IL-6, and on NO-mediated downstream responses.

Suppression of inflammatory cytokine production and oxidative stress by CO-releasing molecules-liberated CO in the small intestine of thermally-injured mice

AIM

To determine whether carbon monoxide (CO)-releasing molecules-liberated CO suppress inflammatory cytokine production and oxidative stress in the small intestine of burnt mice.

METHODS

Twenty-eight mice were assigned to 4 groups. The mice in the sham group (n=7) underwent sham thermal injury, whereas the mice in the burn group (n=7) received 15% total body surface area full-thickness thermal injury, the mice in the burn+CO-releasing molecules (CORM)-2 group (n=7) underwent the same injury with immediate administration of CORM-2 (8 mg/kg, i.v.), and the mice in the burn+inactivated CORM (iCORM)-2 group (n=7) underwent the same injury with immediate administration of iCORM-2. The levels of inflammatory cytokines in the tissue homogenates were measured by ELISA. The levels of malondialdehyde (MDA), nitric oxide (NO) and the expression of inducible nitric oxide synthase (iNOS) in the small intestine were also assessed. In the in vitro experiment, Caco-2 cells were stimulated by experimental mouse sera (50%, v/v) for 4 h. Subsequently, the levels of interleukin (IL)-8 and NO in the supernatants were assessed. Reactive oxygen species (ROS) generation in Caco-2 cells was also measured.

RESULTS

The treatment of burnt mice with CORM-2 significantly attenuated the levels of IL-1beta, TNF-alpha, MDA, and NO in tissue homogenates. This was accompanied by a decrease of iNOS expression. In parallel, the levels of IL-8, NO, and intracellular ROS generation in the supernatants of Caco-2 stimulated by the CORM-2-treated burnt mouse sera was markedly decreased.

CONCLUSION

CORM-released CO attenuates the production of inflammatory cytokines, prevents burn-induced ROS generation, and suppresses the oxidative stress in the small intestine of burnt mice by interfering with the protein expression of iNOS.

Interferon-gamma limits Th1 lymphocyte adhesion to inflamed endothelium: a nitric oxide regulatory feedback mechanism

CD4(+) T helper (Th1 and Th2) cell localization to a site of inflammation is important for the development, maintenance and regulation of an immune response. The factors that regulate Th1 and Th2 cell recruitment into tissue are not fully understood. The aim of the present study was to examine the effect of different cytokine microenvironments on the recruitment of Th1 and Th2 lymphocytes into tissue. Fluorescently labelled Th1 or Th2 lymphocyte-endothelial interactions were observed via intravital microscopy of the cytokine-treated cremaster muscle. Our results show that TNF-alpha alone is sufficient to maximally recruit Th1 cells. Surprisingly, treatment with TNF-alpha + IFN-gamma significantly decreased Th1 adhesion and emigration in comparison to TNF-alpha treatment alone. The decreased adhesion of Th1 cells in response to TNF-alpha + IFN-gamma reflected a decreased ability to bind to ICAM-1 and was iNOS-dependent. This phenomenon was not observed with Th2 cells. These results suggest that IFN-gamma may play a key immunomodulatory role in the recruitment of different T lymphocyte subsets. Indeed, blockade of IFN-gamma or iNOS function during the Th1-mediated contact hypersensitivity response resulted in an acceleration and exacerbation of the late-phase inflammatory response.

L-arginine attenuates acute lung injury after smoke inhalation and burn injury in sheep

Thermal injury results in reduced plasma levels of arginine (Arg). With reduced Arg availability, NOS produces superoxide instead of NO. We hypothesized that Arg supplementation after burn and smoke inhalation (B + S) injury would attenuate the acute insult to the lungs and, thus, protect pulmonary function. Seventeen Suffolk ewes (n = 17) were randomly divided into three groups: (1) sham injury group (n = 6), (2) B + S injury plus saline treatment (n = 6), and (3) B + S injury plus L-ARG infusion at 57 mg.kg(-1).h(-1) (n = 5). Burn and smoke inhalation injury was induced by standardized procedures, including a 40% area full thickness flame burn combined with 48 breaths of smoke from burning cottons. All animals were immediately resuscitated by Ringer solution and supported by mechanical ventilation for 48 h, during which various variables of pulmonary function were monitored. The results demonstrated that Arg treatment attenuated the decline of plasma Arg concentration after B + S injury. A higher plasma Arg concentration was associated with a less decline in Pao2/Fio2 ratio and a reduced extent of airway obstruction after B + S injury. Histopathological examinations also indicated a remarkably reduced histopathological scores associated with B + S injury. Nitrotyrosine stain in lung tissue was positive after B + S injury, but was significantly reduced in the group with Arg. Therefore, L-Arg supplementation improved gas exchange and pulmonary function in ovine after B + S injury via its, at least in part, effect on reduction of oxidative stress through the peroxynitrite pathway.

Metabolism of nitric oxide by Neisseria meningitidis modifies release of NO-regulated cytokines and chemokines by human macrophages

Macrophages produce nitric oxide (NO) via the inducible nitric oxide synthase as part of a successful response to infection. The gene norB of Neisseria meningitidis encodes a NO reductase which enables utilization and consumption of NO during microaerobic respiration and confers resistance to nitrosative stress-related killing by human monocyte-derived macrophages (MDM). In this study we confirmed that NO regulates cytokine and chemokine release by resting MDM: accumulation of TNF-alpha, IL-12, IL-10, CCL5 (RANTES) and CXCL8 (IL-8) in MDM supernatants was significantly modified by the NO-donor S-nitroso-N-penicillamine (SNAP). Using a protein array, infection of MDM with N. meningitidis was shown to be associated with secretion of a wide range of cytokines and chemokines. To test whether NO metabolism by N. meningitidis modifies release of NO-regulated cytokines, we infected MDM with wild-type organisms and an isogenic norB strain. Resulting expression of the cytokines TNF-alpha and IL-12, and the chemokine CXCL8 was increased and production of the cytokine IL-10 and the chemokine CCL5 was decreased in norB-infected MDM, in comparison to wild-type. Addition of SNAP to cultures infected with wild-type mimicked the effect observed in cultures infected with the norB mutant. In conclusion, NorB-catalysed removal of NO modifies cellular release of NO-regulated cytokines and chemokines.

The role of gene-environment interaction in predicting adverse pregnancy outcome

This article focuses on the influence of gene-environment interaction on pregnancy outcome. In particular, we focus on those adverse outcomes related to subclinical infection and the resultant inflammation of gestational tissues. We identify genetic association studies on pregnancy-related disorders with an infectious/inflammatory etiology. All studies in this field have focused on spontaneous preterm delivery and/or preterm and premature rupture of membranes. We discuss those articles where an environmental (infectious) exposure was studied in relation to genetic variability. In these studies, infectious exposure was defined as altered vaginal flora or bacterial vaginosis (BV). Maternal genomic variations influence both tumor necrosis factor-alpha and interleukin-1beta response to BV-related organisms (anaerobic Gram-negative bacteria and Gardnerella vaginalis in particular) in the vagina and the risk of spontaneous preterm birth. Further studies are warranted to confirm these associations, stratify disease risk, and delineate interventions for achieving population health benefits.

Vaginal nitric oxide in pregnant women with bacterial vaginosis

PROBLEM

To evaluate vaginal nitric oxide (NO) production in response to alterations in the vaginal microbial flora.

METHOD OF STUDY

Cervicovaginal lavage samples from 206 women at 18-22 weeks of gestation were tested for NO, interleukin-1beta (IL-1beta), IL-1 receptor antagonist (IL-1ra), tumor necrosis factor-alpha and the inducible 70 kDa heat shock protein (hsp70). Bacterial vaginosis (BV) was diagnosed based on gram staining of vaginal smears.

RESULTS AND CONCLUSIONS

Elevated NO (>2.14 mmol/L) was associated with a diagnosis of BV (38% versus 11%, P < 0.008) as well as an increased median vaginal IL-1ra concentration (72.5 ng/ml versus 36.6 ng/ml, P = 0.041). Elevated vaginal NO was also associated with vaginal hsp70 and this relationship was independent of BV status or IL-1ra concentrations (P < 0.026). We conclude that vaginal hsp70 release in response to abnormal vaginal microflora may trigger NO production in an attempt to minimize the pathological consequences of this altered milieu.

Protective effects of ulinastatin on proliferation and cytokine release of splenocytes from rats with severe acute pancreatitis

AIM

To clarify the contributions of ulinastatin to cellular immune responses in vivo, we examined the functional alterations of splenocytes and quantitatively evaluated the effects of ulinastatin on the splenocyte function during experimental severe acute pancreatitis.

METHODS

Severe acute pancreatitis was induced in rats by retrograde injection of 3% sodium deoxycholate. Thirty minutes after induction of pancreatitis, the rats were randomly assigned to four groups, receiving either saline or 50,000 U/kg of ulinastatin, respectively. Splenocytes were obtained aseptically and stimulated with concanavalin A for 24 h. Then the proliferative activity of cultured splenocytes was measured by using an MTT cellular proliferation assay, and the cytokine concentrations in the culture supernatants were measured by enzyme-linked immunosorbent assays.

RESULTS

Upon stimulation, the release of interleukin-2, interleukin-10, and interferon-gamma was significantly decreased in the splenocytes from rats with pancreatitis as compared with those from sham operation and control groups. The splenocyte proliferation was also significantly suppressed in this group. In contrast, the proliferative as well as the cytokine-releasing capacities of the splenocytes from rats treated with ulinastatin were significantly increased as compared with those from rats with pancreatitis.

CONCLUSIONS

The deficiencies in proliferation and cytokine release in response to antigen stimulation demonstrated an anergic state of splenocytes during severe acute pancreatitis. Treatment with ulinastatin contributed to the recovery of the immune function by improving proliferative responses and cytokine release of splenocytes. These data suggest that a protease-modulating therapy may be an effective strategy for the treatment of immunosuppression induced by severe acute pancreatitis.

Nitric oxide contributes to the development of a post-injury Th2 T-cell phenotype and immune dysfunction

Severe injury induces immune dysfunction resulting in increased susceptibility to opportunistic infections. Previous studies from our laboratory have demonstrated that post-burn immunosuppression is mediated by nitric oxide (NO) due to the increased expression of macrophage inducible nitric oxide synthase (iNOS). In contrast, others suggest that injury causes a phenotypic imbalance in the regulation of Th1- and Th2 immune responses. It is unclear whether or not these apparently divergent mediators of immunosuppression are interrelated. To study this, C57BL/6 mice were subjected to major burn injury and splenocytes were isolated 7 days later and stimulated with antiCD3. Burn injury induced NO-mediated suppression of proliferative responses that was reversed in the presence of the NOS inhibitor L-monomethyl-L-arginine and subsequently mimicked by the addition of the NO donor, S-nitroso-N-acetyl-penicillamine (SNAP). SNAP also dose-dependently suppressed IFN-gamma and IL-2 (Th1), but not IL-4 and IL-10 (Th2) production. Delaying the addition of SNAP to the cultures by 24 h prevented the suppression of IFN-gamma production. The Th2 shift in immune phenotype was independent of cGMP and apoptosis. The addition of SNAP to cell cultures also induced apoptosis, attenuated mitochondrial oxidative metabolism and induced mitochondrial membrane depolarization. However, these detrimental cellular effects of NO were observed only at supra-physiologic concentrations (>250 microM). In conclusion, these findings support the concept that NO induces suppression of cell-mediated immune responses by selective action on Th1 T cells, thereby promoting a Th2 response.