Polyamine involvement in functional activation of human macrophages

Methylglyoxal-bis-guanylhydrazone inhibits osteopontin expression and differentiation in cultured human monocytes

Monocyte activation and polarization play essential roles in many chronic inflammatory diseases. An imbalance of M1 and M2 macrophage activation (pro-inflammatory and alternatively activated, respectively) is believed to be a key aspect in the etiology of these diseases, thus a therapeutic approach that regulates macrophage activation could be of broad clinical relevance. Methylglyoxal-bis-guanylhydrazone (MGBG), a regulator of polyamine metabolism, has recently been shown to be concentrated in monocytes and macrophages, and interfere with HIV integration into the DNA of these cells in vitro. RNA expression analysis of monocytes from HIV+ and control donors with or without MGBG treatment revealed the only gene to be consistently down regulated by MGBG to be osteopontin (OPN). The elevated expression of this pro-inflammatory cytokine and monocyte chemoattractant is associated with various chronic inflammatory diseases. We demonstrate that MGBG is a potent inhibitor of secreted OPN (sOPN) in cultured monocytes with 50% inhibition achieved at 0.1 μM of the drug. Furthermore, inhibition of OPN RNA transcription in monocyte cultures occurs at similar concentrations of the drug. During differentiation of monocytes into macrophages in vitro, monocytes express cell surface CD16 and the cells undergo limited DNA synthesis as measured by uptake of BrdU. MGBG inhibited both activities at similar doses to those regulating OPN expression. In addition, monocyte treatment with MGBG inhibited differentiation into both M1 and M2 classes of macrophages at non-toxic doses. The inhibition of differentiation and anti-OPN effects of MGBG were specific for monocytes in that differentiated macrophages were nearly resistant to MGBG activities. Thus MGBG may have potential therapeutic utility in reducing or normalizing OPN levels and regulating monocyte activation in diseases that involve chronic inflammation.

An oral form of methylglyoxal-bis-guanylhydrazone reduces monocyte activation and traffic to the dorsal root ganglia in a primate model of HIV-peripheral neuropathy

Peripheral neuropathy (PN) is a major comorbidity of HIV infection that is caused in part by chronic immune activation. HIV-PN is associated with infiltration of monocytes/macrophages to the dorsal root ganglia (DRG) causing neuronal loss and formation of Nageotte nodules. Here, we used an oral form of methylglyoxal-bis-guanylhydrazone (MGBG), a polyamine biosynthesis inhibitor, to specifically reduce activation of myeloid cells. MGBG is selectively taken up by monocyte/macrophages in vitro and inhibits HIV p24 expression and DNA viral integration in macrophages. Here, MGBG was administered to nine SIV-infected, CD8-depleted rhesus macaques at 21 days post-infection (dpi). An additional nine SIV-infected, CD8-depleted rhesus macaques were used as untreated controls. Cell traffic to tissues was measured by in vivo BrdU pulse labeling. MGBG treatment significantly diminished DRG histopathology and reduced the number of CD68+ and CD163+ macrophages in DRG tissue. The number of recently trafficked BrdU+ cells in the DRG was significantly reduced with MGBG treatment. Despite diminished DRG pathology, intraepidermal nerve fiber density (IENFD) did not recover after treatment with MGBG. These data suggest that MGBG alleviated DRG pathology and inflammation.

Inhibition of HIV Expression and Integration in Macrophages by Methylglyoxal-Bis-Guanylhydrazone

Macrophages are a target for infection with HIV and represent one of the viral reservoirs that are relatively resistant to current antiretroviral drugs. Here we demonstrate that methylglyoxal-bis-guanylhydrazone (MGBG), a polyamine analog and potent S-adenosylmethionine decarboxylase inhibitor, decreases HIV expression in monocytes and macrophages. MGBG is selectively concentrated by these cells through a mechanism consistent with active transport by the polyamine transporter. Using a macrophage-tropic reporter virus tagged with the enhanced green fluorescent protein, we demonstrate that MGBG decreases the frequency of HIV-infected cells. The effect is dose dependent and correlates with the production of HIV p24 in culture supernatants. This anti-HIV effect was further confirmed using three macrophage-tropic primary HIV isolates. Viral life cycle mapping studies show that MGBG inhibits HIV DNA integration into the cellular DNA in both monocytes and macrophages.

IMPORTANCE

Our work demonstrates for the first time the selective concentration of MGBG by monocytes/macrophages, leading to the inhibition of HIV-1 expression and a reduction in proviral load within macrophage cultures. These results suggest that MGBG may be useful in adjunctive macrophage-targeted therapy for HIV infection.

Polyamines affect histamine synthesis during early stages of IL-3-induced bone marrow cell differentiation

Mast cells synthesize and store histamine, a key immunomodulatory mediator. Polyamines are essential for every living cell. Previously, we detected an antagonistic relationship between the metabolisms of these amines in established mast cell and basophilic cell lines. Here, we used the IL-3-driven mouse bone marrow-derived mast cell (BMMC) culture system to further investigate this antagonism in a mast cell model of deeper physiological significance. Polyamines and histamine levels followed opposite profiles along the bone marrow cell cultures leading to BMMCs. alpha-Difluoromethylornithine (DFMO)-induced polyamine depletion resulted in an upregulation of histidine decarboxylase (HDC, the histamine-synthesizing enzyme) expression and activity, accompanied by increased histamine levels, specifically during early stages of these cell cultures, where an active histamine synthesis process occurs. In contrast, DFMO did not induce any effect in either HDC activity or histamine levels of differentiated BMMCs or C57.1 mast cells, that exhibit a nearly inactive histamine synthesis rate. Sequence-specific DNA methylation analysis revealed that the DFMO-induced HDC mRNA upregulation observed in early bone marrow cell cultures is not attributable to a demethylation of the gene promoter caused by the pharmacological polyamine depletion. Taken together, the results support an inverse relationship between histamine and polyamine metabolisms during the bone marrow cell cultures leading to BMMCs and, moreover, suggest that the regulation of the histamine synthesis occurring during the early stages of these cultures depends on the concentrations of polyamines.

Induction of arginase I and II in bleomycin-induced fibrosis of mouse lung

Arginase, which hydrolyzes arginine to urea and ornithine, is a precursor for the synthesis of polyamines and proline, which is abundant in collagen. The supply of proline can be a crucial factor in the process of lung fibrosis. We investigated the induction of arginine metabolic enzymes in bleomycin-induced mouse lung fibrosis. Histological studies and quantification of lung hydroxyproline showed that lung fibrosis develops in up to 14 days after bleomycin treatment. Under these conditions, collagen I mRNA was induced gradually in up to 15 days, and the content of hydroxyproline reached a maximum at 10 days. Arginase I mRNA was undetectable before bleomycin treatment but was induced 5-10 days after this treatment. Arginase I protein was induced at 7 days and remained little changed for up to 10 days and decreased at 14 days. On the other hand, arginase II mRNA that was detectable before treatment was increased gradually for up to 10 days and decreased at 14 days. Arginase II protein began to increase at day 5, increased for up to 10 days, and was decreased at day 14. mRNAs for cationic amino acid transporter-2 and ornithine decarboxylase were induced in a manner similar to that seen with collagen I mRNA. Immunohistochemical analysis showed that arginase I is induced in macrophages, whereas arginase II is induced in various cell types, including macrophages and myofibroblasts, and roughly colocalizes with the collagen-specific chaperone heat shock protein 47. Our findings suggest that arginine metabolic enzymes play an important role in the development of lung fibrosis, at least in mice.

Evidence that glutamine modulates respiratory burst in stressed rat polymorphonuclear cells through its metabolism into arginine

Glutamine (GLN) and arginine (ARG) are recognized for their ability to modulate immune cell function. However, the metabolic pathways involved in their action remain unclear. It was recently shown that GLN- or ARG-enriched diets increased radical oxygen species (ROS) production by neutrophils from stressed rats. Since these two amino acids have a tied metabolism, we hypothesized that conversion between GLN and ARG (and its active metabolites NO* and polyamines) might be involved. To test this hypothesis male Sprague-Dawley rats (n 117) were randomized into thirteen groups: rats in eleven groups were rendered catabolic by dexamethasone injection (1.5 mg/kg per d for 5 d) and 6.8 mmol either GLN, ARG or non-essential amino acids (NEAA; glycine, alanine and histidine)/kg per d were given by the enteral route; one group was pair-fed to the treated groups. The regimens of all the groups were rendered isonitrogenous by the addition of NEAA. The last group was not treated and was fed ad libitum. For each supplementation three subgroups were formed, each of which received a specific inhibitor: methionine sulfoximine (inhibitor of GLN synthase; 100 mg/kg per d), S-methylthiourea (inhibitor of inducible NO* synthase (iNOS); 50 mg/kg per d) and difluoromethylornithine (inhibitor of ornithine decarboxylase (ODC); 50 mg/kg per d). Oxidative metabolism, intracellular H2O2, and extracellular O2*- production were measured in unstimulated and phorbol myristate acetate-stimulated polymorphonuclear neutrophils. GLN- and ARG-enriched diets increased respiratory burst by neutrophils (oxidative metabolism of 152 (sem 24) and 138 (sem 45) v. 57 (sem 18) mV for GLN-, ARG- and NEAA-enriched diets respectively, P<0.05). In vivo inhibition of iNOS or ODC decreased ROS production induced by GLN and ARG. In vivo inhibition of GLN synthase did not modify the effect of ARG on ROS production. In conclusion, GLN and ARG modulate ROS production in neutrophils from stressed rats by the same pathway involving polyamine and NO* synthesis.

Induction of the arginine decarboxylase ADC2 gene provides evidence for the involvement of polyamines in the wound response in Arabidopsis

Polyamines are small ubiquitous molecules that have been involved in nearly all developmental processes, including the stress response. Nevertheless, no direct evidence of a role of polyamines in the wound response has been described. We have studied the expression of genes involved in polyamine biosynthesis in response to mechanical injury. An increase in the expression of the arginine decarboxylase 2 (ADC2) gene in response to mechanical wounding and methyl jasmonate (JA) treatment in Arabidopsis was detected by using DNA microarray and RNA gel-blot analysis. No induction was observed for the ADC1 gene or other genes coding for spermidine and spermine synthases, suggesting that ADC2 is the only gene of polyamine biosynthesis involved in the wounding response mediated by JA. A transient increase in the level of free putrescine followed the increase in the mRNA level for ADC2. A decrease in the level of free spermine, coincident with the increase in putrescine after wounding, was also observed. Abscisic acid effected a strong induction on ADC2 expression and had no effect on ADC1 expression. Wound-induction of ADC2 mRNA was not prevented in the JA-insensitive coi1 mutant. The different pattern of expression of ADC2 gene in wild-type and coi1 mutant might be due to the dual regulation of ADC2 by abscisic acid and JA signaling pathways. This is the first direct evidence of a function of polyamines in the wound-response, and it opens a new aspect of polyamines in plant biology.

Regulation of macrophage activation and inflammation by spermine: a new chapter in an old story

Spermine, a naturally occurring polyamine, is a ubiquitous structural component of all eukaryotic cells. Regenerating tissues produce higher levels of spermine, and injured or dying cells release spermine into the extracellular milieu, so that tissue levels increase significantly at inflammatory sites of infection or injury. Recent research has focused on delineating the significance of spermine accumulation in the inflammatory process. The discovery that spermine is a negative regulator of macrophage activation provided a mechanism by which spermine influences the biology of inflammation. Mechanistic studies indicate that spermine is incorporated into macrophages and restrains the innate immune response. This anti-inflammatory process is facilitated by the negative acute-phase protein, fetuin.

Microglial responses after focal radiation-induced injury are affected by alpha-difluoromethylornithine

PURPOSE

The objective of this study was to quantify microglial and astrocytic cell responses after focal 125I irradiation of normal brain and to determine the effects of an intravenous infusion of alpha-difluoromethylornithine (DFMO) on those responses.

METHODS AND MATERIALS

Adult beagle dogs were irradiated using high activity 125I sources. Saline or DFMO (75 mg/kg/day) was infused for 18 days, and 1 to 10 weeks later brain tissues were collected. Immunohistochemical stains were used to label phagocytes and amoeboid microglia (lectin RCA-1), astrocytes (GFAP), and cells synthesizing deoxyribonucleic acid (DNA) (BrdU). Cell densities (cells/mm2) and BrdU labeling indices were quantified.

RESULTS

In dogs infused with saline, increases in phagocytes and amoeboid microglia were observed at 1-2 weeks and 4 weeks, respectively. The labeling indices for phagocytes and amoeboid microglia peaked at 4 weeks with maximum values of 4.8 and 13.4%, respectively. Astrocyte cell numbers increased from 2-6 weeks following irradiation; increased labeling indices were observed after 2 weeks. An infusion of DFMO significantly suppressed BrdU labeling and delayed the increase in cell numbers for phagocytes and amoeboid microglia. In both treatment groups, the proportion of total BrdU labeling accounted for by phagocytes was maximum 1 week after irradiation and then decreased. The proportion of total BrdU labeling accounted for by amoeboid microglia and astrocytes was zero for 2 weeks and then increased.

CONCLUSIONS

Microglial reactions after focal irradiation involve the phagocytic and amoeboid cell forms and are characterized by increased BrdU uptake and increased cell number. DFMO significantly alters these responses. Changes in astrocyte cell number and BrdU labeling may be related to changes in microglia. Studies of cell responses and their modification may lead to a better understanding of the pathogenesis of radiation injury, and to new strategies to optimize the use of therapeutic irradiation.

Cellular proliferation and infiltration following interstitial irradiation of normal dog brain is altered by an inhibitor of polyamine synthesis

PURPOSE

The objectives of this study were to quantitatively define proliferative and infiltrative cell responses after focal 125I irradiation of normal brain, and to determine the effects of an intravenous infusion of alpha-difluoromethylornithine (DFMO) on those responses.

METHODS AND MATERIALS

Adult beagle dogs were irradiated using high activity 125I sources. Saline (control) or DFMO (150 mg/kg/day) was infused for 18 days starting 2 days before irradiation. At varying times up to 8 weeks after irradiation, brain tissues were collected and the cell responses in and around the focal lesion were quantified. Immunohistochemical stains were used to label astrocytes (GFAP), vascular endothelial cells (Factor VIII), polymorphonuclear leukocytes (PMNs; MAC 387) and cells synthesizing deoxyribonucleic acid (DNA) (BrdU). Cellular responses were quantified using a histomorphometric analysis.

RESULTS

After radiation alone, cellular events included a substantial acute inflammatory response followed by increased BrdU labeling and progressive increases in numbers of capillaries and astrocytes. alpha-Difluoromethylornithine treatment significantly affected the measured cell responses. As in controls, an early inflammatory response was measured, but after 2 weeks there were more PMNs/unit area than in controls. The onset of measurable BrdU labeling was delayed in DFMO-treated animals, and the magnitude of labeling was significantly reduced. Increases in astrocyte and vessel numbers/mm2 were observed after a 2-week delay. At the site of implant, astrocytes from DFMO-treated dogs were significantly smaller than those from controls.

CONCLUSIONS

There is substantial cell proliferation and infiltration in response to interstitial irradiation of normal brain, and these responses are significantly altered by DFMO treatment. Although the precise mechanisms by which DFMO exerts its effects in this model are not known, the results from this study suggest that modification of radiation injury may be possible by manipulating the response of normal cells to injury.

Characterization of amine oxidase activities in macrophages from human peripheral blood

A sensitive assay for the determination of hydrogen peroxide formation and a method for the identification and characterization of amine oxidases in cells and other oxidase sources of limited accessibility are described. The enzymes are characterized by substrate and inhibitor patterns. The method was applied to the identification and characterization of polyamine oxidizing enzymes in macrophages from human peripheral blood. The major oxidase activity in these cells was found to be a tissue-type polyamine oxidase, but with distinct characteristics. Diamine oxidase and monoamine oxidase activities were also detected in homogenates of macrophages. Since the formation of toxic products by a releasable polyamine oxidase is supposed to be an integral part of a regulatory function of macrophages, we consider our work as a basis for the elucidation of this function.

Polyamine transport in human promyelocytic leukemia cells and polymorphonuclear leukocytes

We examined the kinetics of polyamine uptake by human myeloid cells at different stages of maturity. The Km values of putrescine, spermidine and spermine transport by HL-60 cells were 52, 7.9 and 8.1 microM, respectively. These values decreased to 5.1, 1.7 and 0.77 microM, respectively, in HL-60 cells induced to mature past the promyelocyte stage by DMSO. In human PMNs, the respective Km values were 501, 479 and 381 microM. Transport by HL-60 cells was enhanced when intracellular polyamine levels were reduced with difluoromethylornithine. Thus, HL-60 cell maturation is accompanied by an increase in the affinity of their polyamine transport system. This system is much more efficient than that found in end-stage PMNs, suggesting that it plays a more important role in supporting the metabolic requirements of HL-60 cells. Alternatively, the low affinity of the PMN polyamine transport system could represent an adaptation to the high polyamine concentrations found at infection sites.

Possible role of the transcription factor interferon regulatory factor 1 (IRF-1) in the regulation of ornithine decarboxylase (ODC) gene expression during IFN gamma macrophage activation

In this report we discuss the role of interferon regulatory factor 1 (IRF-1) in the regulation of ornithine decarboxylase (ODC) transcription during IFN gamma human macrophage activation. We show that a binding sequence for the transcription factor IRF-1 is contained in the first intron of the human ODC gene (from nt +2711 to nt +2722) and we demonstrate that the level of expression of IRF-1 increases in human macrophages and in the human promonocytic cell line, U937, previously differentiated in monocytes/macrophages by phorbol myristate acetate (PMA), after 2 h of IFN gamma stimulation. We also show that the hamster tk-ts13 cell line, stably transfected with the IRF-1 cDNA, over-expresses ODC. In addition, a specific complex was detected, by gel-shift assay after incubating a 20 bp double-stranded oligomer containing the binding sequence for IRF-1 with nuclear proteins extracted from human macrophages and from (PMA-differentiated) U937 cells stimulated with IFN gamma for 2 h.

Expression of ornithine decarboxylase gene in elderly human monocytes

The proliferative capacity of the immune system is impaired in elderly subjects and the expression of various genes involved in cell cycle progression is reduced in PHA stimulated lymphocytes during the aging process. Macrophages play a fundamental role in the immune system response. It has recently been demonstrated that the process of macrophage activation is accompanied by a rapid, transient rise of ornithine decarboxylase (ODC) mRNA levels. In fact, the ODC gene seems to be involved in macrophage activation and differentiation. The authors demonstrated that the steady-state levels of ODC mRNA and the correlated superoxide anion production are lower in the monocytes of elderly subjects with respect to those in young subjects used as control. These results confirmed the impaired immune function of the elderly.