Concomitant transcriptional activation of nitric oxide synthase and heme oxygenase genes during nitric oxide-mediated macrophage cytostasis

Chemokine nitration prevents intratumoral infiltration of antigen-specific T cells

Blocking CCL2 nitration in tumors promoted CD8⁺ influx and reduced tumor growth and prolonged survival in mice when combined with adoptive cell therapy.

Tumor-promoted constraints negatively affect cytotoxic T lymphocyte (CTL) trafficking to the tumor core and, as a result, inhibit tumor killing. The production of reactive nitrogen species (RNS) within the tumor microenvironment has been reported in mouse and human cancers. We describe a novel RNS-dependent posttranslational modification of chemokines that has a profound impact on leukocyte recruitment to mouse and human tumors. Intratumoral RNS production induces CCL2 chemokine nitration and hinders T cell infiltration, resulting in the trapping of tumor-specific T cells in the stroma that surrounds cancer cells. Preconditioning of the tumor microenvironment with novel drugs that inhibit CCL2 modification facilitates CTL invasion of the tumor, suggesting that these drugs may be effective in cancer immunotherapy. Our results unveil an unexpected mechanism of tumor evasion and introduce new avenues for cancer immunotherapy.

Hyperbaric oxygen attenuation of lipopolysaccharide-induced acute lung injury involves heme oxygenase-1

BACKGROUND

Hyperbaric oxygen (HBO) attenuates lipopolysaccharide (LPS)-induced acute lung injury. This beneficial effect of HBO involves inhibition of inducible nitric oxide synthase (iNOS) expression and subsequent nitric oxide (NO) biosynthesis. We sought to investigate the role of heme oxygenase-1 (HO-1) on this HBO inhibition of iNOS induction and acute lung injury in septic rat lungs.

METHODS

Before the experiment, 72 rats were randomly allocated to receive HBO or air treatment. With or without HBO pre-treatment, the rats were further divided into the following subgroups (n = 6): (i) LPS injection, (ii) normal saline (N/S) injection, (iii) hemin (a HO-1 inducer) plus LPS, (iv) hemin alone, (v) tin protoporphyrin (SnPP; a HO-1 inhibitor) plus LPS, and (vi) SnPP alone. All rats were maintained for 6 h and then sacrificed with a high-dose pentobarbital injection. Lung injuries and relevant enzymes expression were thus assayed.

RESULTS

Histological analysis, PMNs/alveoli ratio, and wet/dry weight ratio measurements demonstrated that LPS caused significant lung injury and HBO and/or hemin significantly attenuated this LPS-induced lung injury. Increased pulmonary iNOS expression and NO production were associated with lung injury. Induction of HO-1, by HBO and/or hemin, significantly attenuated this LPS-induced iNOS expression and acute lung injury. SnPP, on the contrary, offset the effects of HBO and worsened the LPS-induced lung injury.

CONCLUSIONS

HBO may act through inhibiting pulmonary iNOS expression to attenuate LPS-induced acute lung injury in septic rats. Furthermore, this HBO attenuation of iNOS expression involves HO-1 induction.

Immunoprotective haem oxygenase induction by ultraviolet A (320-400 nm) radiation in the mouse is inhibited in interferon-gamma null mice

BACKGROUND

A protective role for the ultraviolet (UV) A waveband against immunosuppression induced by UVB (280-320 nm) radiation has been identified. The mechanism for UVA immunoprotection was found to involve two apparently unrelated mediators, the T-helper-1-associated proinflammatory cytokine interferon (IFN)-gamma and the UVA-induced redox-regulated stress protein, haem oxygenase (HO).

OBJECTIVES

To identify a relationship between these two immune regulators.

METHODS

The HO response to UVA radiation in the skin and liver was examined in mice with a targeted disruption of the IFN-gamma gene, known to be unresponsive to UVA photoimmunoprotection. Results IFN-gamma null mice did not respond to UVA irradiation with the normal upregulation of HO activity in either the irradiated skin or the liver. Injection of these mice with recombinant IFN-gamma previously shown to restore the UVA-photoimmunoprotective effect, here partially and dose-responsively restored their ability for induction of HO activity in both skin and liver following UVA irradiation.

CONCLUSIONS

IFN-gamma appears to be a prerequisite for the immunoprotective induction of HO, although other mediators may also be involved. The UVA responsiveness of HO in an internal organ such as the liver suggests the existence of a soluble UVA-induced mediator from the skin, which may be IFN-gamma.

A DNA microarray study of nitric oxide-induced genes in mouse hepatocytes: implications for hepatic heme oxygenase-1 expression in ischemia/reperfusion

Nitric oxide (NO) can modulate numerous genes directly; however, some genes may be modulated only in the presence of the inflammatory stimuli that increase the expression of the inducible nitric oxide synthase (iNOS). One method by which to examine changes in NO-mediated gene expression is to carry out a gene array analysis on NO-nai;ve cells. Herein, we report a gene array analysis on mRNA from iNOS-null (iNOS(-/-)) mouse hepatocytes harvested from mice exposed to NO by infection with an adenovirus expressing human iNOS (Ad-iNOS). Of the 6500 genes on this array, only approximately 200 were modulated either up or down by the increased iNOS activity according to our criteria for significance. Several clearly defined families of genes were modulated, including genes coding for proinflammatory transcription factors, cytokines, cytokine receptors, proteins associated with cell proliferation and cellular energetics, as well as proteins involved in apoptosis. Our results suggest that iNOS has a generally anti-inflammatory and anti-apoptotic role in hepatocytes but also acts to suppress proliferation and protein synthesis. The expression of iNOS results in increased expression of stress-related proteins, including heme oxygenase-1 (HO-1). We used HO-1 to confirm that a significant change identified by an analysis could be demonstrated as significant in cells and tissues. The elevation of HO-1 was confirmed at the protein level in hepatocytes in vitro. Furthermore, iNOS(-/-) mice experienced greatly increased liver injury subsequent to intestinal ischemia/reperfusion injury, associated with an inability to upregulate HO-1. This is the first study to address the global gene changes induced by iNOS in any cell type, and the findings presented herein may have clinical relevance for conditions such as septic or hemorrhagic shock in which hepatocytes, NO, and HO-1 play a crucial role.

Assessment of immune function by lymphoproliferation underestimates lymphocyte functional capacity in HIV patients treated with highly active antiretroviral therapy

The objective of this study was to evaluate T cell responses in HIV-infected patients after highly active antiretroviral therapy (HAART), using four assays of immune function, and to determine which best reflects the presence of CD4(+) T cells able to respond to CMV antigen. Peripheral blood mononuclear cells from 41 HIVinfected patients and 31 healthy HIV-seronegative controls were cultured with mitogen (PMA/Ca(2+) ionophore) or antigen (CMV). Production of interferon gamma (IFN-gamma) determined by ELISpot assay was compared with lymphoproliferation, IFN-gamma production assessed by ELISA, and CD69 expression and intracellular IFN-gamma assessed by flow cytometry. Cells from patients whose CD4(+) T cells counts increased 4-fold or to >200 cells/microl after HAART responded as well as control cells when assessed by IFN-gamma production and CD69 expression after mitogenic stimulation, but lymphoproliferation responses were depressed by about 52%. Patients who did not meet these criteria for immune reconstitution had lymphoproliferative responses up to 30-fold lower than control subjects, while intracellular IFN-gamma and CD69 expression and ELISpot counts were less than 3-fold lower. Responses to CMV antigen could not be detected by flow cytometry, but were readily detected by ELISpot in CMV-seropositive patients whose CD4(+) T cell counts had increased after HAART. This included patients with low responses assessed by lymphoproliferation. Moreover, ELISpot responses measured with fresh and frozen cells were comparable, while lymphoproliferation assays required fresh cells. In conclusion, the ELISpot assay is a sensitive and efficient technique for detecting CMV-specific IFN-gamma responses in samples that display poor responses when assessed by lymphoproliferation assays.

Nitric-oxide dioxygenase activity and function of flavohemoglobins. sensitivity to nitric oxide and carbon monoxide inhibition

Widely distributed flavohemoglobins (flavoHbs) function as NO dioxygenases and confer upon cells a resistance to NO toxicity. FlavoHbs from Saccharomyces cerevisiae, Alcaligenes eutrophus, and Escherichia coli share similar spectra, O(2), NO, and CO binding kinetics, and steady-state NO dioxygenation kinetics. Turnover numbers (V(max)) for S. cerevisiae, A. eutrophus, and E. coli flavoHbs are 112, 290, and 365 NO heme(-1) s(-1), respectively, at 37 degrees C with 200 microm O(2). The K(M) values for NO are low and range from 0.1 to 0.25 microm. V(max)/K(M)(NO) ratios of 900-2900 microm(-1) s(-1) indicate an extremely efficient dioxygenation mechanism. Approximate K(M) values for O(2) range from 60 to 90 microm. NO inhibits the dioxygenases at NO:O(2) ratios of > or =1:100 and makes true K(M)(O(2)) values difficult to determine. High and roughly equal second order rate constants for O(2) and NO association with the reduced flavoHbs (17-50 microm(-1) s(-1)) and small NO dissociation rate constants suggest that NO inhibits the dioxygenase reaction by forming inactive flavoHbNO complexes. Carbon monoxide also binds reduced flavoHbs with high affinity and competitively inhibits NO dioxygenases with respect to O(2) (K(I)(CO) = approximately 1 microm). These results suggest that flavoHbs and related hemoglobins evolved as NO detoxifying components of nitrogen metabolism capable of discriminating O(2) from inhibitory NO and CO.

Mitochondrial DNA damage as a mechanism of cell loss in Alzheimer's disease

Aging is associated with impaired mitochondrial function caused by accumulation of oxygen free radical-induced mitochondrial (Mt) DNA mutations. One prevailing theory is that age-associated diseases, including Alzheimer's disease (AD), may be precipitated, propagated, or caused by impaired mitochondrial function. To investigate the role of MtDNA relative to genomic (Gn) DNA damage in AD, temporal lobe samples from postmortem AD (n = 37) and control (n = 25) brains were analyzed for MtDNA and GnDNA fragmentation, mitochondrial protein and cytochrome oxidase expression, MitoTracker Green fluorescence (to assess mitochondrial mass/abundance), and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-OHdG) immunoreactivity. Brains with AD had more extensive nicking and fragmentation of both MtDNA and GnDNA as demonstrated by agarose gel electrophoresis, end-labeling, and the in situ terminal deoxynucleotide transferase end-labeling (TUNEL) assay, and only the brains with AD had detectable 8-OHdG immunoreactivity in cortical neurons. Increased MtDNA damage in AD was associated with reduced MtDNA content, as demonstrated by semiquantitative PCR analysis and reduced levels of Mt protein and cytochrome oxidase expression by Western blot analysis or immunohistochemical staining with image analysis. The finding of reduced MitoTracker Green fluorescence in AD brains provided additional evidence that reduced Mt mass/abundance occurs with AD neurodegeneration. The presence of increased MtDNA and GnDNA damage in AD suggest dual cell death cascades in AD. Impaired mitochondrial function caused by MtDNA damage may render brain cells in AD more susceptible to oxidative injury and thereby provide a mechanism by which systemic or environmental factors could influence the course of disease.

Physical exercise-induced expression of inducible nitric oxide synthase and heme oxygenase-1 in human leukocytes: effects of RRR-alpha-tocopherol supplementation

This study evaluated the effects of RRR-alpha-tocopherol (500 IU/day, 8 days) on in vivo cytokine response and cytoplasmic expression of inducible nitric oxide synthase (iNOS) and the antioxidant stress protein heme oxygenase-1 (HO-1) in human leukocytes after exhaustive exercise. Thirteen men were investigated in a double-blind, placebo-controlled, cross-over study with a wash-out period of 28 days. The exercise procedure consisted of an incremental treadmill test followed by a continuous run until exhaustion at 110% of the individual anaerobic threshold (total duration 28.5 +/- 0.8 min). HO-1 and iNOS protein were assessed in mono- (M), lympho-, and granulocytes (G) using flow cytometry. Plasma interleukin-6 (IL-6) and IL-8 were measured by ELISA. IL-6 rose significantly whereas IL-8 did not exhibit significant changes after exercise. Changes of IL-6 were not affected by RRR-alpha-tocopherol. Exercise induced an increase of iNOS protein primarily in M and G. A small, but significant, increase of HO-1 protein was measured in M and G. RRR-alpha-Tocopherol did not show any significant effects on cytoplasmic expression of iNOS and HO-1 at rest and after exercise. In conclusion, exhaustive exercise induces expression of iNOS and HO-1 in human leukocytes by a mechanism that is not sensitive to RRR-alpha-tocopherol supplementation.

Nitric oxide induces heme oxygenase-1 gene expression in mesangial cells

BACKGROUND

Nitric oxide (NO) release as a result of activation of inducible NO synthase (iNOS) can be sustained and reach cytotoxic concentrations. It is unknown whether cells possess intrinsic systems to attenuate NO-mediated cytotoxicity. One potential system is the heme oxygenase-1 (HO-1) enzyme because it catabolizes heme and therefore may limit synthesis or availability of iNOS. These studies were undertaken to explore whether NO derived from NO donors or from activation of iNOS induces HO-1 in mesangial cells.

METHODS

The expression of the HO-1 gene was evaluated at the mRNA (Northern blot analysis) and protein (Western blot analysis) levels in mesangial cells treated with two NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetyl-DL-penicillamine (SNAP), or was stimulated by the combination of lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) to induce iNOS in the presence and absence of NOS inhibitor NG-Monomethyl-L-arginine (L-NMMA).

RESULTS

HO-1 was constitutively expressed in mesangial cells. Both SNP and SNAP induced HO-1 mRNA in a dose-dependent manner. The increase in mRNA was associated with an increase in HO-1 protein in SNP-treated cells. The combination of the LPS/IFN-gamma mixture induced iNOS expression and NO production in murine mesangial cells, as assessed by Western blot analysis and measurement of nitrite levels. HO-1 expression was also increased in response to LPS/IFN-gamma. L-NMMA dose dependently attenuated HO-1 mRNA and protein levels. In contrast, iNOS expression was dose dependently enhanced.

CONCLUSIONS

Our studies demonstrate that both exogenously or iNOS-derived NO enhance HO-1 expression in mesangial cells and point to regulatory interactions between the iNOS and HO pathways. HO-1 activation may defend against NO-mediated toxicity.

Regulation of intracellular polyamine biosynthesis and transport by NO and cytokines TNF-alpha and IFN-gamma

Nitric oxide (NO) has been described to exert cytostatic effects on cellular proliferation; however the mechanisms responsible for these effects have yet to be fully resolved. Polyamines, conversely, are required components of cellular proliferation. In experimental models of inflammation, a relationship between these two pathways has been suggested by the temporal regulation of a common precursor, arginine. This study was undertaken to determine the effects NO and the NO synthase (NOS)-inducing cytokines, tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), exert on polyamine regulation. The transformed kidney proximal tubule cell line, MCT, maintains high constitutive levels of the first polyamine biosynthetic enzyme, ornithine decarboxylase (ODC). NO donors markedly suppressed ODC activity in MCT and all other cell lines examined. TNF-alpha and IFN-gamma induction of NO generation resulted in suppressed ODC activity, an effect prevented by the inducible NOS inhibitor L-N6-(1-iminoethyl)lysine (L-NIL). Dithiothreitol reversal of NO-mediated ODC suppression supports nitrosylation as the mechanism of inactivation. We also evaluated polyamine uptake, inasmuch as inhibition of ODC can result in a compensatory induction of polyamine transporters. Administration of NO donors, or TNF-alpha and IFN-gamma, suppressed [3H]putrescine uptake, thereby preventing transport-mediated reestablishment of intracellular polyamine levels. This study demonstrates the capacity of NO and inflammatory cytokines to regulate both polyamine biosynthesis and transport.

Nitric oxide mediates the lipopolysaccharide dependent upregulation of the heme oxygenase-1 gene expression in cultured rat Kupffer cells

BACKGROUND/AIMS

Heme oxygenase catalyzes the rate-limiting enzymatic step of heme degradation. The inducible isoform of heme oxygenase, heme oxygenase-1, is expressed at a low level in most tissues and is upregulated by its substrate heme and various stress stimuli. Kupffer cells which represent the largest population of the body's tissue macrophages serve physiological functions in the defense against various pathogens such as lipopolysaccharide. The goal of the present study was to investigate the heme oxygenase-1 gene expression in Kupffer cells of rat liver and in isolated Kupffer cell cultures during treatment with lipopolysaccharide.

METHODS

Cryostat sections of normal rat liver were investigated by immunofluorescence double-staining using specific antibodies for rat heme oxygenase-1 and ED2. Isolation and cell culture of Kupffer cells and primary hepatocytes from rat liver, as well as Northern and Western blot analysis, were performed with standard protocols.

RESULTS

Heme oxygenase-1 protein was highly expressed in large sinusoidal cells of normal rat liver, which were identified as Kupffer cells by staining with the macrophage surface marker ED2. By contrast, no expression of heme oxygenase-1 was detected in liver parenchymal cells. High expression of heme oxygenase-1 was also found in isolated Kupffer cells in culture by immunocytochemical staining as well as by Western and Northern blot analysis. After treatment of Kupffer cells cultures with lipopolysaccharide, heme oxygenase-1 was upregulated on the protein and mRNA level in a time- and dose-dependent manner. This increase in heme oxygenase-1 expression by lipopolysaccharide was prevented by the nitric oxide inhibitor N(G)-monomethyl-L-arginine which was reversed by an excess of L-arginine. Various nitric oxide donors up-regulated heme oxygenase-1 mRNA expression in Kupffer cells.

CONCLUSIONS

The lipopolysaccharide-dependent upregulation of the heme oxygenase-1 gene which is highly expressed in Kupffer cells is mediated by a nitric oxide-dependent mechanism.

Heme and the endothelium. Effects of nitric oxide on catalytic iron and heme degradation by heme oxygenase

We studied the effects of nitric oxide (NO) on the control of excess cellular heme and release of catalytically active iron. Endothelial cells (ECs) exposed to hemin followed by a NO donor have a ferritin content that is 16% that of cells exposed to hemin alone. Hemin-treated ECs experience a 3.5-fold rise in non-heme, catalytic iron 2 h later, but a hemin rechallenge 20 h later results in only a 24% increase. The addition of a NO donor after the first hemin exposure prevents this adaptive response, presumably due to effects on ferritin synthesis. NO donors were found to reduce iron release from hemin, while hemin accumulated in cells. A NO donor, in a dose-dependent fashion, inhibited heme oxygenase activity, measured by bilirubin production. Using low temperature EPR spectroscopy, heme oxygenase inhibition correlated with nitrosylation of free heme in microsomes. Nitrosylation of cellular heme prevented iron release, for while there was heme oxygenase-dependent release of iron in cells incubated with hemin for 24 h, the addition of a NO donor blocked iron release. This indicates that NO readily nitrosylates intracellular free heme and prevents its degradation by heme oxygenase. Nitrosylation of heme was found to reduce sensitization of cells to oxidative injury.

Inhibition of Inducible Nitric Oxide Synthase by Peroxisome Proliferator-Activated Receptor Agonists: Correlation with Induction of Heme Oxygenase 1

Genetic knock-out in mice of peroxisome proliferator-activated receptor-α (PPARα) can prolong inflammation in response to leukotriene B4. Although cyclooxygenase 2 has been shown to be induced by PPAR activation, the effect of PPAR agonists on the key inflammatory enzyme systems of nitric oxide synthase (NOS) and stress proteins has not been investigated. The effect on these of naturally occurring eicosanoid PPAR agonists (leukotriene B4 and 8(S)-hydroxyeicosatetraenoic acid, which are PPARα selective; PGA2, PGD2, PGJ2, and Δ12PGJ2, which are PPARγ selective) and the synthetic PPARα agonist Wy14,643 was examined in activated RAW264.7 murine macrophages. Leukotriene B4 and 8(S)-hydroxyeicosatetraenoic acid stimulated nitrite accumulation, indicative of enhanced NOS activity. PGA2, PGD2, PGJ2, Δ12PGJ2, and Wy14,643 reduced nitrite accumulation, with Δ12PGJ2 being the most effective. The mechanism behind this reduction was examined using Western blotting. Inhibition of nitrite accumulation was associated with a fall in inducible NOS protein and an induction of heme oxygenase 1, correlating both dose dependently and temporally. Other proteins examined (cyclooxygenase 2, heme oxygenase 2, heat shock protein 70, and glucose-regulated protein 78) were unaffected. The data suggest that naturally occurring PPAR agonists can inhibit the inducible NOS enzyme pathway. This inhibition may be mediated by modulation of the stress protein, heme oxygenase 1. Thus, the generation of eicosanoid breakdown products during inflammation may contribute to its eventual resolution by activation of the PPAR system. This system may thus represent a novel target for therapeutic intervention in inflammatory disease.