Macrophage Tumoricidal Activity Research Articles

Novel sulfated polysaccharide derived from red-tide microalga Gyrodinium impudicum strain KG03 with immunostimulating activity in vivo

The high-sulfate-containing exopolysaccharide p-KG03 is produced by the red-tide microalga Gyrodinium impudicum strain KG03. The immunostimulatory effects of this sulfated exopolysaccharide were investigated by isolating peritoneal macrophages from mice 10 or 20 days after they had received a single dose of p-KG03 (100 or 200 mg/kg body weight). The cytotoxicity of the isolated macrophages for B16 tumor cells was tested, as B16 tumor cells are sensitive to tumor necrosis factor alpha (TNF-alpha) and nitric oxide. The activities of natural killer cells from the p-KG03-treated mice against YAC-1 mouse lymphoma cells were also tested. The nonspecific immune functions mediated by natural killer cells and macrophages were increased by treatment with p-KG03 in vivo. These results suggest that p-KG03 has immunostimulatory effects and enhances the tumoricidal activities of macrophages and NK cells in vivo. In addition, p-KG03 treatment increased the plaque-forming cell response to sheep red blood cells, as well as the levels of IgM and IgG Exposure to p-KG03 also increased the production by macrophages of cytokines, such as interleukins -1beta and -6, and TNF-alpha. This is the first report of a marine microalgal sulfated polysaccharide having immunostimulatory activities. The p-KG03 polysaccharide may be useful for the development of biotechnological and pharmaceutical products that incorporate bioactive marine exopolysaccharides.

Pathophysiological roles of macrophage migration inhibitory factor in gastrointestinal, hepatic, and pancreatic disorders

Macrophage migration inhibitory factor (MIF) is a unique protein, participating in inflammation, immune response, and cell growth. MIF was first discovered as a lymphokine involved in delayed hypersensitivity and various macrophage functions, including phagocytosis, spreading, and tumoricidal activity. It has been reported that MIF is associated with the pathogenesis of a variety of diseases. MIF expression was increased at inflammatory sites in diseases such as rheumatoid arthritis and glomerulonephritis. In experimental inflammatory disease, blockade of MIF bioactivity inhibited the severity of disease activity. On the other hand, MIF expression is also increased in tumor lesions, and MIF plays a role as a cell growth factor. MIF has been reported to be constitutively expressed in gut, liver, and pancreas. In patients with gastritis, inflammatory bowel disease, hepatitis, and pancreatitis, MIF expression was remarkably increased in both the serum and the local lesions. Blockade of MIF bioactivity inhibited and prevented inflammation in experimental gastritis, colitis, hepatitis, and pancreatitis. On the other hand, MIF expression was higher than that in normal tissues in colonic carcinomas and hepatocellular carcinoma both in vivo and in vitro. Blockade of MIF bioactivity successfully inhibited tumor cell growth in vivo and in vitro. MIF plays important roles in the pathogenesis of gastrointestinal, hepatic, and pancreatic disorders.

Enhancement of Antitumor Effects of Paclitaxel (Taxol) in Combination with Red Ginseng Acidic Polysaccharide (RGAP)

We have recently reported that red ginseng acidic polysaccharide (RGAP), isolated from Korean red ginseng (Panax ginseng C.A. Meyer), shows immunomodulatory and antitumor activities, mainly mediated by the nitric oxide (NO) production of macrophages. This compound may be used in cancer therapy alone or in combination with other chemotherapeutic agents. The synergistic effect of RGAP and paclitaxel (taxol) was evaluated to develop new biological response modifiers in cancer therapy. The present study demonstrates a synergistic antitumor effect of RGAP and paclitaxel in mice transplanted with sarcoma 180 and B16 melanoma. Combined treatment with paclitaxel (5 or 15 mg/kg) and RGAP (25 mg/kg) resulted in a 28.6 or 42.8 % increase in the life span of ICR mice bearing sarcoma 180 tumor cells, while no obvious effect was seen on sole paclitaxel treatment. When a combination of paclitaxel (10 mg/kg) and RGAP (100 mg/kg) was administered to C57BL/6 mice implanted with B16 melanoma, the tumor weight per mouse also decreased by 76.3 %, suggesting that RGAP may be used as an adjuvant in medicinal applications of paclitaxel. The augmented antitumor effect of paclitaxel is supposed to be the result of the immunomodulating antitumor effect of RGAP. RGAP, having B cell specific mitogenic activity, induced the secretion of interleukin-6 (IL-6) in spleen cells in a concentration-dependent manner (5 to 500 microg/microL). RGAP also restored the proliferation of splenocytes and NK cell activity suppressed by paclitaxel. Flow cytometric analysis of splenocytes in mice treated with paclitaxel showed a significant increase of CD11b+ cells. Additionally, a synergistic effect of RGAP and paclitaxel was found to effect an increased tumoricidal activity of macrophages. The above results suggest that clinical trials of RGAP as an adjuvant in cancer chemotherapy of paclitaxel are highly feasible.

Differential Expression of PKC Isoforms and Their Tumoricidal Activity in Two Macrophage Cell Lines: Involvement of Nitric Oxide-dependent Mechanisms

Objective: To investigate the role of PKC isoforms in the regulation of LPS-triggered tumoricidal activity in macrophages and further elucidate its signal mechanisms. Methods: Two macrophage cell lines (P388D1 and RAW264.7) were stimulated by LPS alone, or with long-term of PMA pretreatment. Then cytotoxicities to P815 cells (by MTT assay) and IL-1, TNF-α (by ELISA) and nitric oxide (NO) production (by Griess reagent) in supernatants were measured. Western blot for PKC isoforms after long-term PMA pretreatment was analyzed. Results: RAW264.7 cells were stimulated with LPS to kill target tumor cells P815, whereas P388D1 cells failed to develop such an ability. Down-regulation of PKC isoforms by chronic treatment with PMA significantly inhibited the LPS-induced cytotoxicity in RAW264.7 cells. In unstimulated state, Western blotting with rabbit antiserum specific for the PKCα, β1, β2, δ or e showed all 5 isoforms were detected in P388D1 cells, while only PKCα, PKCβ1 and PKCδ were detected in RAW264.7 cells. Exposure of the cells to long-term of PMA treatment significantly down-regulated the expression of PKCα, PKCβ1 and PKCδ in RAW264.7 cells. But in P388D1 cells, although PKCα, PKCδ and PKCe were down-regulated, the expression of PKCβ1 and PKCβ2 could not be regulated. Comparing with LPS-induced IL-1, TNF- and NO production by the two macrophage cell lines, P388D1 failed to produce NO. In RAW264.7 cells, LPS-induced NO production and antitumor activity was attenuated by the addition of L-NAME, an iNOS inhibitor. Conclusion: The results indicated a critical role of PKCβ in LPS-induced antitumor activity and this cytotoxicity is mainly due to PKC-β mediated NO production by RAW264.7 cells, but not a direct cytotoxic activity.

Inhaled isobutyl nitrite inhibited macrophage inducible nitric oxide by blocking NFκB signaling and promoting degradation of inducible nitric oxide synthase-2

We previously reported that inhaled isobutyl nitrite inhibited macrophage tumoricidal activity by inhibiting inducible nitric oxide (NO) production. In the present study, a much shorter inhalant exposure regimen (five daily exposures) inhibited inducible NO and the NO synthase (NOS2). One of the ways in which NO and NOS2 are regulated is by ubiquitin-dependent NOS2 degradation. Immunoprecipitated NOS2 showed increased poly-ubiquitination, following exposure to the inhalant. In addition, Western blots of macrophage nuclear extracts for the NFκB subunit, p65, showed that exposure to the inhalant inhibited NFκB signaling, necessary for induction of NOS2. The inhalant blocked phosphorylation of the NFκB inhibitor, IκBα. The inhibition of NFκB signaling following inhalant exposure was confirmed using mice transgenic for the κB-dependent promoter of the HIV 5′ LTR linked to luciferase. The data suggested that inhalant exposure likely inhibited macrophage NO production by blocking NFκB-mediated activation signaling and promoting poly ubiquitination of NOS2.

Inhaled isobutyl nitrite inhibited macrophage inducible nitric oxide by blocking NF$kappa;B signaling and promoting degradation of inducible nitric oxide synthase-2

We previously reported that inhaled isobutyl nitrite inhibited macrophage tumoricidal activity by inhibiting inducible nitric oxide (NO) production. In the present study, a much shorter inhalant exposure regimen (five daily exposures) inhibited inducible NO and the NO synthase (NOS2). One of the ways in which NO and NOS2 are regulated is by ubiquitin-dependent NOS2 degradation. Immunoprecipitated NOS2 showed increased poly-ubiquitination, following exposure to the inhalant. In addition, Western blots of macrophage nuclear extracts for the NFκB subunit, p65, showed that exposure to the inhalant inhibited NFκB signaling, necessary for induction of NOS2. The inhalant blocked phosphorylation of the NFκB inhibitor, IκBα. The inhibition of NFκB signaling following inhalant exposure was confirmed using mice transgenic for the κB-dependent promoter of the HIV 5′ LTR linked to luciferase. The data suggested that inhalant exposure likely inhibited macrophage NO production by blocking NFκB-mediated activation signaling and promoting poly ubiquitination of NOS2.

Acidic polysaccharide isolated from Phellinus linteus induces nitric oxide-mediated tumoricidal activity of macrophages through protein tyrosine kinase and protein kinase C

Mushroom polysaccharides are increasingly being utilized to treat a wide variety of diseases. Aqueous extracts from the Phellinus linteus have been reported to have anti-tumor and immunomodulatory properties. In particular, acidic polysaccharide (PL) isolated from P. linteus induced a secretory and cellular macrophage response. However, the exact mechanism by which PL regulates the macrophage functions remains unclear. PL-treated murine peritoneal macrophages in vitro and in vivo dramatically induced the production of NO. PL enhanced the lytic death of B16 cells through the production of NO. The present study examined signal molecules that may participate in PL-elicited responses by macrophages. The data demonstrated that a protein kinase C (PKC) inhibitor, staurosporine, and a protein tyrosine kinase (PTK) inhibitor, genistein, inhibited the tumoricidal activity of macrophages induced by PL. In addition, these inhibitors blocked the production of NO and the expression of surface molecules in PL-stimulated macrophages. Furthermore, CD11b/CD18 possibly mediates PL-induced cell activation. These results suggest that PL stimulates NO production for tumoricidal activity and induces cell-mediated immunity by increasing surface molecules, and the process may be a mechanism by which PL produces its therapeutic effects.

Treatment with Propionibacterium acnes modulates the late phase reaction of immediate hypersensitivity in mice

The administration of killed Propionibacterium acnes suspension to mice enhances macrophage phagocytic and tumoricidal activities, have an adjuvant effect to antibody response and increases resistance to infection. Recent reports demonstrated that P. acnes treatment promotes IL-12 and IL-18 synthesis in mice inducing IFN-γ release, enhancement of IgG2a switch and inhibition of Th2 cell expansion. These findings led us to investigate whether P. acnes could modulate hypersensitivity type I reaction observed in a murine model. Animals were implanted with heat coagulated hen's egg white (HEW) into the subcutaneous tissue, followed by OVA-challenge in the footpad. The observed reaction was characterized by elevated Th2 cytokine levels, especially IL-4 and increase in eosinophil infiltration as occurs in the late phase reaction (LPR) of type I hypersensitivity, a pattern observed in allergic asthma in human. Two different biological effects were induced by killed P. acnes depending on the experimental protocol used. When mice were treated with one dose of P. acnes per week during 3 weeks and the last dose administrated at the same time of HEW implantation, a strong adjuvant effect on type I hypersensitivity reaction with intense eosinophilic infiltration was observed. On the other hand, when the HEW implant was made 1 week after the administration of the last dose of P. acnes, animals developed a typical delayed type hypersensitivity reaction, and a cytokines pattern characteristic of the Th1 immune response.

Cyclooxygenase-2 inhibition improves macrophage function in melanoma and increases the antineoplastic activity of interferon gamma.

Melanoma inhibits macrophage tumoricidal activity and increases the expression of cyclooxygenase-2 (COX-2). In this study, we sought to determine whether inhibition of COX-2 could restore macrophage function and hence maximize the antitumor activity of the immune stimulant interferon gamma (IFN gamma). Peritoneal macrophages were exposed to B16 melanoma-conditioned medium for 24 hours with or without the COX-2 inhibitor NS-398 and then were stimulated with lipopolysaccharide and IFN gamma. Cytotoxic activity, nitrite production, and cytokine production by the stimulated macrophages were measured. In addition, B16 melanoma cells were implanted intradermally into mice treated with IFN gamma (14,000 U on alternate days) alone or with a combination of IFN gamma and a COX-2 inhibitor (NS-398 or nimesulide). Mice were assessed for tumor growth and survival. Macrophage cytotoxicity and nitrite production were significantly suppressed by melanoma-conditioned medium (P <.01). This was prevented by 200 micro M of NS-398 (P <.05). In vivo, combined treatment with IFN gamma and a COX-2 inhibitor caused a significant inhibition of tumor growth (P <.01) and improved survival (P =.02) compared with controls. COX-2 inhibition reversed melanoma-induced suppression of macrophage function, and combined treatment of IFN gamma plus a COX-2 inhibitor was maximally effective in reducing tumor growth and improving survival.

Characterization of human Gc protein-derived macrophage activation factor (GcMAF) and its functional role in macrophage tumoricidal activity.

Macrophages are essential for host defense and play an important role in orchestrating immune response of the host against threat signals. Macrophages are also known to have a critical role in antitumor immunity, can infiltrate into tumor, and are found in most tumor sites. Meanwhile, Gc protein (also known as vitamin D-binding protein) is a serum protein with multifunctional properties and has been reported as a precursor for macrophage activation factor. Gc protein can be converted by an inducible s-galactosidase of B cells and neuraminidase of T cells to a potent macrophage activating factor (GcMAF), a protein with N-acetylgalactosamine (GaINAc) as the remaining sugar moiety. Activated macrophages express tumoricidal activity by ingestion of tumor cells and release of reactive oxygen species (ROS) and reactive nitrogen species (RNS), or both. We reported that in situ modification of Gc protein with B-galactosidase and neuraminidase increased the release of superoxide in thioglycolate-elucidated mouse peritoneal macrophage. Yamamoto et al. reported the possibility of using GcMAF as an immunomodulator for cancer treatment, so it is important to provide an assay for GcMAF. Kanan et al. reported the quantitative analysis of GcMAF from human serum. However, the sugar moiety of GcMAF has never been qualitatively studied. Here we present the study of qualitative analysis of GcMAF from purified human serum as well as its influence on the macrophage activity.

Suppression of in vivo tumorigenicity of rat hepatoma cell line KDH-8 cells by soluble TGF-beta receptor type II.

We have previously reported that transforming growth factor beta (TGF-beta) produced by rat hepatoma cell line KDH-8 cells suppressed the interleukin-2 (IL-2) production of T cells and the tumoricidal activity of macrophages in KDH-8 tumor-bearing rats and that the inhibition of TGF-beta production by low-dose bleomycin restored these activities significantly. In this study, we established three transfectant clones with stable expression of soluble TGF-beta receptor type II (sTRII), namely KT1, KT2 and KT3, and one with an empty vector used as control vector (KV), and then investigated the effects of sTRII on the tumorigenicity of KDH-8 cells and immune responses in syngeneic Wistar King Aptekman/Hok (WKAH) rats. We found that sTRII expressed in sTRII transfectants could abolish growth inhibition of Mv1Lu cells by TGF-beta1 produced by the cells themselves, and that tumor growth of KT2 and KT3 clones in vivo was suppressed significantly compared with that of parent, KV and KT1 clones. Furthermore, we demonstrated that IL-2 production of splenocytes and IL12p40 mRNA expression in tumor tissues were restored in rats inoculated with KT2 and KT3 clones, whereas such restoration was not observed in rats inoculated with parent, KV and KT1 clones. Combined with a low expression of sTRII in KT1 tumor tissues, these results suggest that sTRII may to some extent be able to abolish the tumor-promoting activity of TGF-beta, and imply that sTRII might have a therapeutic effect on TGF-beta-producing tumors.

ANTITUMOR EFFECTS OF THE INTRAVESICAL INSTILLATION OF HEAT KILLED CELLS OF THE LACTOBACILLUS CASEI STRAIN SHIROTA ON THE MURINE ORTHOTOPIC BLADDER TUMOR MBT-2

To characterize the potential of heat killed Lactobacillus casei, Shirota strain (LC9018), as an alternative to bacillus Calmette-Guerin (BCG) for treating patients with bladder cancer we investigated the antitumor effects of intravesical instillation of LC9018 in the MBT-2 orthotopic bladder tumor implantation model in C3H/He mice. LC9018 or BCG, Tokyo 172 strain, was instilled once daily for 10 days starting on the day after orthotopic implantation of MBT-2. Tumor appearance and mean bladder weight on day 21 after tumor implantation were evaluated. Moreover, we investigated the augmentation of local cellular immunity in bladder mucosa by immunohistochemical staining and reverse transcription polymerase chain reaction. Intravesical LC9018 instillation significantly reduced the rate of tumor appearance in 8 of 38 subjects (p <0.001) and mean tumor growth plus or minus standard deviation with a bladder weight of 37 +/- 49 mg. (p <0.001) compared with tumor appearance in 41 of 58 subjects and mean bladder weight 146 +/- 183 mg. in controls. BCG had no significant antitumor activity in the orthotopic implantation model. Intravesical instillation of LC9018 augmented the local expression of antitumor cytokine messenger RNA (interferon-gamma and tumor necrosis factor-alpha) and induced the infiltration of neutrophils surrounded by macrophages that phagocytosed LC9018 cells at the bladder mucosa. These results suggest that LC9018 is potentially more potent and safer as a therapeutic agent than BCG for superficial bladder tumors. Furthermore, the antitumor effect of LC9018 is exerted via the augmentation of local cell mediated antitumor immunity.

Involvement of protein kinase C and tyrosin kinase in tumoricidal activation of macrophage induced by Streptococcus pneumoniae type II capsular polysaccharide

Capsular polysaccharide type 2 (PS) from Streptococcus pnemoniae induced the secretory and cellular macrophage response. However, the exact mechanism by which PS regulates the macrophage functions remains unclear. In this study, we examined signal molecules which may participate in PS-elicited responses by macrophages. Our data demonstrated that tumoricidal activation of macrophages induced by PS was inhibited by either protein kinase C (PKC) inhibitor, H7 or protein tyrosine kinase (PTK) inhibitor, genistein. In addition, these inhibitors blocked the production of TNF-α and NO in PS-stimulated macrophages. Furthermore, PS-induced cell activation is possibly mediated by Toll-like receptor 2. These data suggest that PKC and PTK are involved in the activation of macrophages with PS.

IFN-gamma-independent autocrine cytokine regulatory mechanism in reprogramming of macrophage responses to bacterial lipopolysaccharide.

Macrophages are now well recognized to have a critical role in both innate and acquired immunity. The sentinel macrophage function is highly regulated and serves to allow for intrinsic plasticity of the innate immune responses to potential environmental signals. However, the mechanisms underlying the dynamic properties of the cellular arm of innate immunity are poorly understood. Therefore, we have conducted a series of in vitro studies to evaluate the contribution of immunoregulatory cytokines, such as IFN-gamma, IL-10, and IL-12, in modulation of macrophage responses. We found that macrophages from IFN-gamma knockout (IFN-gamma(-/-)) mice exhibit only marginal LPS-induced TNF-alpha, IL-12, and NO responses, all of which can be fully restored in the presence of rIFN-gamma. Pretreatment with substimulatory LPS concentrations led to reprogramming of IFN-gamma(-/-) macrophage responses in a dose-dependent manner that manifested by an increased TNF-alpha and IL-12, but not NO, production upon the subsequent LPS challenge. These reprogramming effects were substantially attenuated and profoundly enhanced in macrophages from IL-12(-/-) and IL-10(-/-) mice, respectively, as compared with those modulated in macrophages from the congenic wild-type mice. LPS-dependent reprogramming was also fully reproduced in macrophages isolated from SCID mice after immunodepletion of NK cells. Our data strongly imply that cytokine (TNF-alpha and IL-12), but not NO, responses in macrophages may, at least in part, be governed by an autocrine IFN-gamma-independent regulatory mechanism reciprocally controlled by IL-10 and IL-12. This mechanism may serve as an alternative/coherent pathway to the canonical IFN-gamma-dependent induction of antimicrobial and tumoricidal activity in macrophages.

Macrophage migration inhibitory factor (MIF): its essential role in the immune system and cell growth.

Macrophage migration inhibitory factor (MIF) functions as a pleiotropic protein, participating in inflammatory and immune responses. MIF was originally discovered as a lymphokine involved in delayed hypersensitivity and various macrophage functions, including phagocytosis, spreading, and tumoricidal activity. Recently, MIF was reevaluated as a proinflammatory cytokine and pituitary-derived hormone potentiating endotoxemia. This protein is ubiquitously expressed in various organs, such as the brain and kidney. Among cytokines, MIF is unique in terms of its abundant expression and storage within the cytoplasm and, further, for its counteraction against glucocorticoids. MIF has unexpectedly been found to convert D-dopachrome, an enantiomer of naturally occurring L-dopachrome, to 5,6-dihydroxyindole. However, its physiologic significance remains to be elucidated. It was demonstrated that anti-MIF antibodies effectively suppress tumor growth and tumor-associated angiogenesis, suggesting that MIF is involved not only in inflammatory and immune responses but also in tumor cell growth. At present, MIF cannot be clearly categorized as either a cytokine, hormone, or enzyme. This review presents the latest findings on the role of MIF in the immune system and in cell growth, with regard to tumorigenesis and wound repair, and discusses its potential functions in various pathophysiologic states.

Nitric oxide synthesis and TNF-α secretion in RAW 264.7 macrophages: Mode of action of a fermented papaya preparation

Macrophage inducible nitric oxide synthase is able to generate massive amounts of nitric oxide (NO) which contributes to the host immune defense against viruses and bacteria. Monocyte-macrophages stimulated with the bacterial wall component lipopolysaccharide (LPS) and cytokines such as interferon-γ (IFN-γ) express the inducible form of nitric oxide synthase (iNOS). Furthermore, tumor necrosis factor-α (TNF-α) is one of the central regulatory cytokines in macrophage antimicrobial activity and synergizes with IFN-γ in the induction of NO synthesis. Because of its pivotal role in both antimicrobial and tumoricidal activities of macrophages, a significant effort has focused on developing therapeutic agents that regulate NO production. In the present study fermented papaya preparation (FPP) is shown to exert both immunomodulatory and antioxidant activity in the macrophage cell line RAW 264.7. Interestingly, a low and a high molecular weight fraction (LMF and HMF, respectively) of FPP exhibited different activity patterns. FPP fractions alone did not affect NO production. However in the presence of IFN-γ, both LMF and HMF significantly increased iNOS activity and nitrite as well as nitrate accumulation. NO radical formation measured in real-time by electron paramagnetic resonance spectroscopy was higher in the presence of LMF and IFN-γ. On the contrary, iNOS mRNA levels were enhanced further with HMF than with LMF. Moreover, LMF displayed a stronger superoxide anion scavenging activity than HMF. In the presence of IFN-γ, both FPP fractions stimulated TNF-α secretion. However in non-stimulated macrophages, TNF-α secretion was enhanced by HMF only. Since water-soluble FPP fractions contained no lipid A, present data indicate that FPP is a macrophage activator which augments nitric oxide synthesis and TNF-α secretion independently of lipopolysaccharides.

Intensified regression of colon cancer liver metastases in mice treated with irinotecan and the immunomodulator JBT 3002.

The authors recently reported that tumoricidal activation of macrophages by a new synthetic bacterial lipopeptide, JBT 3002, can augment chemotherapy-mediated tumor-cell killing. The aim of this study was to identify the mechanism responsible for the destruction of metastatic cells. Three daily oral doses of JBT 3002 before once-weekly intraperitoneal injections of 100 mg/kg irinotecan for 3 weeks significantly increased the eradication of established CT-26 murine colon cancer liver metastases compared with treatment with irinotecan alone. Immunohistochemical analyses revealed that the hepatic metastases in mice given combination therapy contained infiltrating CD8+ lymphocytes and a dense infiltrate of macrophages expressing both inducible nitric oxide synthase (iNOS) and interleukin-15. In vitro treatment of peritoneal macrophages with JBT 3002 plus interferon-gamma induced the expression of iNOS and the production of nitric oxide. In the presence of a low (subtoxic) dose of irinotecan, these activated macrophages produced significant lysis of CT-26 cells. The high level of cytotoxicity was inhibited by the specific inducible nitric oxide synthase inhibitor, NG-methyl-L-arginine. In contrast, irinotecan-mediated lysis of normal intestinal epithelial IEC-6 cells was not increased by activated macrophages. Scanning electron microscopy revealed that activated macrophages bound to CT-26 tumor cells but not to normal IEC-6 cells, confirming that nitric oxide-mediated cytotoxicity is specific for tumor cells. Collectively, the results suggest that augmentation of the therapeutic efficacy of irinotecan against colon cancer liver metastases by immunomodulation with JBT 3002 may be associated with elevated inducible nitric oxide synthase and endogenous interleukin-15 in tumor-infiltrating macrophages.

Cryptococcus neoformans neutralizes macrophage and astrocyte derived nitric oxide without interfering with inducible nitric oxide synthase induction or catalytic activity - possible involvement of nitric oxide consumption.

The effect of Cryptococcus neoformans on the accumulation of nitrite, an indicator of nitric oxide (NO) synthesis, was investigated in cytokine (interferon-gamma [IFN-gamma] and interleukin [IL]-1)-stimulated cultures of rat peritoneal macrophages and C6 astrocytoma cells. Cytokine-induced nitrite generation in cultures of both cell types was inhibited in a dose-dependent manner by live C. neoformans, but not by heat-killed cryptococcal cells or conditioned medium from yeast cultures. C. neoformans-mediated reduction of nitrite formation coincided with impairment of NO-dependent macrophage tumoricidal activity. Cytokine-triggered induction of inducible NO synthase (iNOS) was unaffected in C6 cells, and only marginally reduced in macrophages. When cells were pretreated with cytokines for 24 h to induce iNOS, and any further induction was prevented by inhibition of protein synthesis, C. neoformans was still able to reduce nitrite accumulation in cultures of both cell types. Finally, live C. neoformans, but not heat-killed yeast cells or yeast culture supernatant, significantly reduced nitrite production in a culture solution of NO-releasing compound S-nitrosoglutathione (GSNO). Thus, it appears that cryptococcal reduction of nitrite formation in macrophage and C6 cultures was caused by the consumption of NO by some yeast molecule, rather than by the inhibition of cellular NO synthesis.

Nitrite inhalants spontaneously liberate nitric oxide, which is not responsible for the immunotoxicity in C57BL/6 mice

Nitrite inhalant abuse has been correlated epidemiologically with HIV seropositivity and with Kaposi’s sarcoma. Using a mouse model, we have shown that inhaled isobutyl nitrite caused anemia and severely depressed immunity. In the present study, we showed that both isobutyl and cyclohexyl nitrites in air liberated nitric oxide (NO). An immunotoxic dose of 900 ppm isobutyl nitrite liberated 115 ppm NO. Mice were exposed in an inhalation chamber to 115 ppm NO, 900 ppm isobutyl nitrite, or 900 ppm cyclohexyl nitrite for 45 min/day. Following a single exposure, NO did not affect peripheral blood cell counts, while isobutyl and cyclohexyl nitrites reduced cell numbers. After 14 daily exposures, isobutyl nitrite, but not cyclohexyl nitrite or NO, reduced peritoneal macrophage tumoricidal activity. The nitrite esters likely caused immunotoxicity by mechanisms other than NO release.

Mycoplasma arginini enhances cytotoxicity of thioglycollate-elicited murine macrophages toward YAC-1 tumor cells through production of NO

Bacterial products stimulate macrophage tumoricidal activity through release of tumor necrosis factor (TNF) and nitric oxide (NO). We show here that thioglycollate-elicited macrophages acquire cytotoxic activity when cocultured with Mycoplasma arginini-infected YAC-1 tumor cells and release TNF and NO. Fixed mycoplasma-infected cells, supernatants from infected-cell cultures, or purified heat-killed mycoplasma obtained from cell-free cultures were all able to induce TNF and NO production. Thus, the mycoplasma per se and not a product of infected cells induce the release of these molecules. Addition of prostaglandin E2 (PGE2) to the cocultures, which reduced TNF release, or antibodies to TNF, did not affect macrophage cytotoxicity nor NO release. Inhibition of NO production by L-NAME or aminoguanidine reduced the cytotoxicity, and treatment with a NO donor was toxic to YAC-1 cells. These results indicate that M. arginini activates thioglycollate-elicited murine macrophages for NO and TNF release increasing their cytotoxic activity toward YAC-1 cells and that this activity is dependent on NO but not TNF release.