Iron down-regulates macrophage anti-tumour activity by blocking nitric oxide production

A closer look at the role of iron in glioblastoma

Glioblastoma (GBM) is among the deadliest malignancies facing modern oncology. While our understanding of certain aspects of GBM biology has significantly increased over the last decade, other aspects, such as the role of bioactive metals in GBM progression, remain understudied. Iron is the most abundant transition metal found within the earth's crust and plays an intricate role in human physiology owing to its ability to participate in oxidation-reduction reactions. The importance of iron homeostasis in human physiology is apparent when examining the clinical consequences of iron deficiency or iron overload. Despite this, the role of iron in GBM progression has not been well described. Here, we review and synthesize the existing literature examining iron's role in GBM progression and patient outcomes, as well as provide a survey of iron's effects on the major cell types found within the GBM microenvironment at the molecular and cellular level. Iron represents an accessible target given the availability of already approved iron supplements and chelators. Improving our understanding of iron's role in GBM biology may pave the way for iron-modulating approaches to improve patient outcomes.

Targeting iron metabolism in osteosarcoma

Osteosarcoma (OS) is the most common primary solid malignant tumour of bone, with rapid progression and a very poor prognosis. Iron is an essential nutrient that makes it an important player in cellular activities due to its inherent ability to exchange electrons, and its metabolic abnormalities are associated with a variety of diseases. The body tightly regulates iron content at the systemic and cellular levels through various mechanisms to prevent iron deficiency and overload from damaging the body. OS cells regulate various mechanisms to increase the intracellular iron concentration to accelerate proliferation, and some studies have revealed the hidden link between iron metabolism and the occurrence and development of OS. This article briefly describes the process of normal iron metabolism, and focuses on the research progress of abnormal iron metabolism in OS from the systemic and cellular levels.

Ironing Out the Details: How Iron Orchestrates Macrophage Polarization

Iron fine-tunes innate immune responses, including macrophage inflammation. In this review, we summarize the current understanding about the iron in dictating macrophage polarization. Mechanistically, iron orchestrates macrophage polarization through several aspects, including cellular signaling, cellular metabolism, and epigenetic regulation. Therefore, iron modulates the development and progression of multiple macrophage-associated diseases, such as cancer, atherosclerosis, and liver diseases. Collectively, this review highlights the crucial role of iron for macrophage polarization, and indicates the potential application of iron supplementation as an adjuvant therapy in different inflammatory disorders relative to the balance of macrophage polarization.

Risk of cancer in patients with iron deficiency anemia: a nationwide population-based study

Objective

This study evaluated the risk of cancer among patients with iron deficiency anemia (IDA) by using a nationwide population-based data set.

Method

Patients newly diagnosed with IDA and without antecedent cancer between 2000 and 2010 were recruited from the Taiwan National Health Insurance Research Database. The standardized incidence ratios (SIRs) of cancer types among patients with IDA were calculated.

Results

Patients with IDA exhibited an increased overall cancer risk (SIR: 2.15). Subgroup analysis showed that patients of both sexes and in all age groups had an increased SIR. After we excluded patients diagnosed with cancer within the first and first 5 years of IDA diagnosis, the SIRs remained significantly elevated at 1.43 and 1.30, respectively. In addition, the risks of pancreatic (SIR: 2.31), kidney (SIR: 2.23), liver (SIR: 1.94), and bladder cancers (SIR: 1.74) remained significantly increased after exclusion of patients diagnosed with cancer within 5 years after IDA diagnosis.

Conclusion

The overall cancer risk was significantly elevated among patients with IDA. After we excluded patients diagnosed with IDA and cancer within 1 and 5 years, the SIRs remained significantly elevated compared with those of the general population. The increased risk of cancer was not confined to gastrointestinal cancer when the SIRs of pancreatic, kidney, liver, and bladder cancers significantly increased after exclusion of patients diagnosed with IDA and cancer within the first 5 years. This finding may be caused by immune activities altered by IDA. Further study is necessary to determine the association between IDA and cancer risk.

Iron and genome stability: an update

Iron is an essential micronutrient which is required in a relatively narrow range for maintaining metabolic homeostasis and genome stability. Iron participates in oxygen transport and mitochondrial respiration as well as in antioxidant and nucleic acid metabolism. Iron deficiency impairs these biological pathways, leading to oxidative stress and possibly carcinogenesis. Iron overload has been linked to genome instability as well as to cancer risk increase, as seen in hereditary hemochromatosis. Iron is an extremely reactive transition metal that can interact with hydrogen peroxide to generate hydroxyl radicals that form the 8-hydroxy-guanine adduct, cause point mutations as well as DNA single and double strand breaks. Iron overload also induces DNA hypermethylation and can reduce telomere length. The current Recommended Dietary Allowances (RDA) for iron, according with Institute of Medicine Dietary Reference Intake (DRI), is based in the concept of preventing anemia, and ranges from 7mg/day to 18mg/day depending on life stage and gender. Pregnant women need 27mg/day. The maximum safety level for iron intake, the Upper Level (UL), is 40-45mg/day, based on the prevention of gastrointestinal distress associated to high iron intakes. Preliminary evidence indicates that 20mg/day iron, an intake slightly higher than the RDA, may reduce the risk of gastrointestinal cancer in the elderly as well as increasing genome stability in lymphocytes of children and adolescents. Current dietary recommendations do not consider the concept of genome stability which is of concern because damage to the genome has been linked to the origin and progression of many diseases and is the most fundamental pathology. Given the importance of iron for homeostasis and its potential influence over genome stability and cancer it is recommended to conduct further studies that conclusively define these relationships.

NO-induced activation of cyclic GMP-dependent pathway down regulates ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) protein in rat C6 glioma

In rat C6 glioma cells, the ecto-nucleotide pyrophosphatase/phosphodiesterase-1 (NPP1), a modulator of purinergic receptor signaling, is down regulated after an increase in intracellular cAMP by addition of dibutyryl cAMP, a membrane-permeable cAMP-analog, or by activation of the β-adrenoceptor receptor with (-)-isoproterenol (Aerts et al., 2011, Eur. J. Pharmacol. 654, 1-9). In this communication we studied the effect of nitric oxide (NO)/cGMP, a pathway also affecting purinergic receptor signaling, on the level of NPP1 protein. Sodium nitroprusside (SNP), a NO donor, reduces NPP1 protein in a dose-dependent manner. A combination of SNP and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, an inhibitor of soluble guanylate cyclase, demonstrated that NO-dependent down regulation of NPP1 was caused by NO-sensitive guanylyl cyclase. Treatment with Rp-pCPT-cGMPS, an inhibitor of protein kinase G (PKG), showed that PKG is not involved in the down regulation of NPP1. In addition, we have shown that the cAMP- and cGMP-dependent decrease in NPP1 expression is unrelated. These results indicate that NO/cGMP regulates the level of NPP1 protein by a pathway that differs from the cAMP-induced decrease in NPP1.

Biocorrosion properties and blood and cell compatibility of pure iron as a biodegradable biomaterial

Biocorrosion properties and blood- and cell compatibility of pure iron were studied in comparison with 316L stainless steel and Mg-Mn-Zn magnesium alloy to reveal the possibility of pure iron as a biodegradable biomaterial. Both electrochemical and weight loss tests showed that pure iron showed a relatively high corrosion rate at the first several days and then decreased to a low level during the following immersion due to the formation of phosphates on the surface. However, the corrosion of pure iron did not cause significant increase in pH value to the solution. In comparison with 316L and Mg-Mn-Zn alloy, the pure iron exhibited biodegradable property in a moderate corrosion rate. Pure iron possessed similar dynamic blood clotting time, prothrombin time and plasma recalcification time to 316L and Mg-Mn-Zn alloy, but a lower hemolysis ratio and a significant lower number density of adhered platelets. MTT results revealed that the extract except the one with 25% 24 h extract actually displayed toxicity to cells and the toxicity increased with the increasing of the iron ion concentration and the incubation time. It was thought there should be an iron ion concentration threshold in the effect of iron ion on the cell toxicity.

A possible link between iron deficiency and gastrointestinal carcinogenesis

There is definitive evidence that iron overload induces oxidative stress and DNA damage, which can enhance carcinogenic risk. However, other evidence suggests that iron deficiency and anemia also increase oxidative stress and DNA damage, which might increase carcinogenesis risk, especially in the gastrointestinal (GI) tract. The aim of this review is to provide essential background information for the accurate interpretation of future research on iron deficiency and increased GI cancer risk. Based on clinical, epidemiological, and experimental evidence, we discuss how iron deficiency might contribute to increased cancer risk through the impairment of several iron-dependent metabolic functions that are related to genome protection and maintenance (e.g., immune responses against cancer-initiated cells, metabolism of toxic compounds, and redox regulation of DNA biosynthesis and repair). Some epidemiological studies have indicated increased risk of GI tumors among individuals with low iron intake or low somatic iron stores, and in vivo data from rodent cancer models indicates the early progression of GI tumors during iron deficiency. Given the preliminary but consistent evidence relating iron deficiency to cancer risk and the fact that iron deficiency affects about one third of the world's population, further studies are needed to define the extent to which iron deficiency might increase GI cancer risk.

The role of reactive oxygen and nitrogen species in cellular iron metabolism

The catalytic role of iron in the Haber-Weiss chemistry, which results in propagation of damaging reactive oxygen species (ROS), is well established. In this review, we attempt to summarize the recent evidence showing the reverse: That reactive oxygen and nitrogen species can significantly affect iron metabolism. Their interaction with iron-regulatory proteins (IRPs) seems to be one of the essential mechanisms of influencing iron homeostasis. Iron depletion is known to provoke normal iron uptake via IRPs, superoxide and hydrogen peroxide are supposed to cause unnecessary iron uptake by similar mechanism. Furthermore, ROS are able to release iron from iron-containing molecules. On the contrary, nitric oxide (NO) appears to be involved in cellular defense against the iron-mediated ROS generation probably mainly by inducing iron removal from cells. In addition, NO may attenuate the effect of superoxide by mutual reaction, although the reaction product-peroxynitrite-is capable to produce highly reactive hydroxyl radicals.

Correlation of iron and colon adenomas

BACKGROUND AND OBJECTIVE

Better colon cancer screening guidelines are needed. This study was conducted to explore the relationship between serum transferrin saturation (as iron is a potential carcinogen) and presence of colon adenomas. This may aid to evolve better colon cancer screening guidelines.

METHODS

This study is a retrospective review of computer records. Patients who had colonoscopy and iron studies done between May 1996 and December 2003 were included in the study. The adjusted odds ratio, derived from multiple logistic regression analysis, was used to measure the association between transferrin saturation and colon adenomas.

RESULTS

Complete data were available for 124 subjects. The adjusted odds ratio, for predicting the presence of polyp in those patients with transferrin saturation above the median was 10.9 (CI 4.0-29.5, P<0.001). A one percent increase in transferrin saturation was associated with a 1.07 increase the odds of adenoma (CI 1.03-1.11, P<0.001).

CONCLUSIONS

Iron levels are directly linked to presence of colon polyps, and might help in evolving better screening guidelines.

Use of a colorimetric assay to measure differences in cytotoxicity of Mycobacterium tuberculosis strains

Several techniques have been used to quantify the cytotoxicity produced by Mycobacterium tuberculosis bacilli on cell monolayers; however, they are semi-quantitative or time consuming. Herein, a method based on crystal violet (CV) uptake by THP-1 cell monolayers is described. This colorimetric method quantifies the cytotoxic effect as a function of the number of remaining cells after the infection with M. tuberculosis. Since this micro-organism is not stained by the dye, it does not produce a background that affects absorbance readings. As determined by CV assay (CVA), M. tuberculosis strain H37Rv destroyed 10.5 % of THP-1 cell monolayers at 24 h and 50.52 % at 72 h, while M. tuberculosis strains lacking the complete phospholipase C locus produced a reduced cytotoxic effect. The damage estimated by microscopy corresponded to the effect quantified by CVA. The results show that the use of CVA is a rapid, sensitive and reliable quantitative assay to measure the cytotoxicity of different M. tuberculosis strains.

Recurrent headache as the main symptom of acquired cerebral toxoplasmosis in nonhuman immunodeficiency virus-infected subjects with no lymphadenopathy: the parasite may be responsible for the neurogenic inflammation postulated as a cause of different types of headaches

Headache and/or migraine, a common problem in pediatrics and internal medicine, affect about 5% to 10% children and adolescents, and nearly 30% of middle-aged women. Headache is also one of the most common clinical manifestations of acquired Toxoplasma gondii infection of the central nervous system (CNS) in immunosuppressed subjects. We present 11 apparently nonhuman immunodeficiency virus-infected children aged 7 to 17 years (8 girls, 3 boys) and 1 adult woman with recurrent severe headaches in whom latent chronic CNS T. gondii infection not manifested by enlarged peripheral lymph nodes typical for toxoplasmosis, was found. In 7 patients, the mean serum IgG Toxoplasma antibodies concentration was 189 +/- 85 (SD) IU/mL (range 89 to 300 IU/mL), and in 5 other subjects, the indirect fluorescent antibody test titer ranged from 1:40 to 1:5120 IU/mL (n= <1:10 IU/mL). Some of the patients suffered also from atopic dermatitis (AD) and were exposed to cat and/or other pet allergens, associated with an increased IL-4 and decreased IFN-gamma production. These cytokine irregularities caused limited control of cerebral toxoplasmosis probably because IL-4 down-regulated both the production of IFN-gamma and its activity, and stimulated production of a low NO-producing population of monocytes, which allowed cysts rupture, increased parasite multiplication and finally reactivation of T. gondii infection. The immune studies performed in 4 subjects showed a decreased percentage of T lymphocytes, increased total number of lymphocytes B and serum IgM concentration, and impaired phagocytosis. In addition, few of them had also urinary tract diseases known to produce IL-6 that can mediate immunosuppressive functions, involving induction of the anti-inflammatory cytokine IL-10. These disturbances probably resulted from the host protective immune reactions associated with the chronic latent CNS T. gondii infection/inflammation. This is consistent with significantly lower enzyme indoleamine 2,3-dioxygenase (IDO) activity reported in atopic than in nonatopic individuals, and an important role that IDO and tryptophan degradation pathways plays in both, the host resistance to T. gondii infection and its reactivation. Analysis of literature information on the subjects with different types of headaches caused by foods, medications, and other substances, may suggest that their clinical symptoms and changes in laboratory data result at least in part from interference of these factors with dietary tryptophan biotransformation pathways. Several of these agents caused headache attacks through enhancing NO production via the conversion of arginine to citrulline and NO by the inducible nitric oxide synthase enzyme, which results in the high-output pathway of NO synthesis. This increased production of NO is, however, quickly down-regulated by NO itself because this biomolecule can directly inactivate NOS, may inhibit Ia expression on IFN-gamma-activated macrophages, which would limit antigen-presenting capability, and block T-cell proliferation, thus decreasing the antitoxoplasmatic activity. Moreover, NO inhibits IDO activity, thereby suppressing kynurenine formation, and at least one member of the kynurenine pathway, 3-hydroxyanthranilic acid, has been shown to inhibit NOS enzyme activity, the expression of NOS mRNA, and activation of the inflammatory transcription factor, nuclear factor-kB. In addition, the anti-inflammatory cytokines IL-4 and IL-10, TGF-beta, and a cytokine known as macrophage deactivating factor, have been shown to directly modulate NO production, sometimes expressing synergistic activity. On the other hand, IL-4 and TGF-beta can suppress IDO activity in some cells, for example human monocytes and fibroblasts, which is consistent with metabolic pathways controlled by IDO being a significant contributor to the proinflammatory system. Also, it seems that idiopathic intracranial hypertension, pseudotumor cerebri, and aseptic meningitis, induced by various factors, may result from their interference with IDO and inducible nitric oxide synthase activities, endogenous NO level, and cytokine irregularities which finally affect former T. gondii status 2mo in the brain. All these biochemical disturbances caused by the CNS T. gondii infection/inflammation may also be responsible for the relationship found between neurologic symptoms, such as headache, vertigo, and syncope observed in apparently immunocompetent children and adolescents, and physical and psychiatric symptoms in adulthood. We therefore believe that tests for T. gondii should be performed obligatorily in apparently immunocompetent patients with different types of headaches, even if they have no enlarged peripheral lymph nodes. This may help to avoid overlooking this treatable cause of the CNS disease, markedly reduce costs of hospitalization, diagnosis and treatment, and eventually prevent developing serious neurologic and psychiatric disorders.

Enhanced cytotoxic activity of macrophages and suppressed tumor metastases in mice irradiated with low doses of X- rays

We showed in our previous report that a single exposure of mice to 0.1 or 0.2 Gy X-rays led to the significant inhibition of the development of artificial tumor metastases in the lungs and that the effect was related to the enhanced activity of natural killer cells. In the present study, a possible involvement of cytotoxic macrophages in the anti-metastatic effect of the low-level X-ray exposures was investigated. We now demonstrate that irradiation of mice with either of the two low doses of X-rays significantly stimulates the macrophage-mediated cytolysis of the susceptible tumor targets and that the effect coincides with the enhanced production of nitric oxide in the collected effector cells. We also show that suppression of the in vivo function of macrophages by carrageenan eliminates the inhibitory effect of the two low doses of X-rays on the development of pulmonary tumor colonies as well as significantly suppresses the macrophage-mediated cytotoxicity and nitric oxide production. Finally, aminoguanidine added to the culture medium of the assayed macrophages not only shuts down the nitric oxide synthesis in these cells but also significantly suppresses their cytolytic activity. Overall, the obtained results indicate that inhibition of the tumor metastases by a single exposure of mice to 0.1 or 0.2 Gy X-rays results, to a large extent, from the radiation-induced stimulation of the cytocidal activity of macrophages which secrete enhanced amounts of nitric oxide.

Requirement for multiple activation signals by anti-inflammatory feedback in macrophages

Pathogen killing is one of the primary roles of macrophages, utilizing potent effectors such as nitric oxide (NO) and involving other cellular machinery including iron regulatory apparatus. Macrophages become strongly activated upon receipt of appropriate signaling with cytokines and pathogen-derived endotoxins. However, they must resist activation in the absence of decisive signaling due to the energetic demands of activation coupled with the toxic nature of effector molecules to surrounding tissues. We have developed a mathematical model of the modular biochemical network of macrophages involved with activation, pathogen killing and iron regulation. This model requires synergistic interaction of multiple activation signals to overcome the quiescent state. To achieve a trade-off between macrophage quiescence and activation, strong activation signals are modulated via negative regulation by NO. In this way a single activation signal is insufficient for complete activation. In addition, our results suggest that iron regulation is usually controlled by activation signals. However, under conditions of partial macrophage activation, exogenous iron levels play a key role in regulating NO production. This model will be useful for evaluating macrophage control of intracellular pathogens in addition to the biochemical mechanisms examined here.

Acidosis affects tumor cell survival through modulation of nitric oxide release

The influence of environmental pH on the production of tumoricidal free radical nitric oxide (NO) was investigated in mouse fibrosarcoma L929 and rat glioma C6 cell lines. A combination of IFN-gamma and IL-1 induced a significant NO release and subsequent reduction of cell viability in tumor cell lines. Acidification of cell culture medium reduced tumor cell NO production in a pH-dependent manner. While the inhibitory effect of acidosis on NO production in C6 cells was associated with a further decrease in cell viability, it completely rescued L929 cells from NO-dependent apoptotic and necrotic death. Acidic pH diminished IFN-gamma+ IL-1-induced expression of inducible NO synthase (iNOS) mRNA and protein, and abolished the activation of iNOS transcription factor IRF-1 in L929 cells. Moreover, extracellular acidosis significantly impaired cytokine-induced phosphorylation of MAP kinase p44/42 (ERK1/2) and subsequent expression of transcription factor c-Fos in L929 cells. Finally, mild acidosis (pH 6.8) augmented, while severe acidosis (pH 6.0) reduced, IFN-gamma-induced iNOS activation/NO release and NO-dependent anticancer activity of rat and mouse macrophages. Taken together, our findings indicate that modulation of macrophage and tumor cell iNOS by an acidic microenvironment might influence the progression of NO-sensitive solid tumors.

The Mechanisms of 6-Hydroxydopamine-Induced Astrocyte Death

Treatment with 6-hydroxydopamine significantly reduced the viability of cultured rat primary astrocytes, rat astrocytoma cell line C6, and human astrocytoma cell line U251. 6-Hydroxydopamine-treated astrocytes exhibited altered nuclear morphology, DNA fragmentation, and reduced intracellular esterase activity, which indicated apoptotic cell death. Astrocytes were protected by neutralization of 6-hydroxydopamine autooxidation products H(2)O(2), O(2)(*-), and (*)OH, but not by cell-derived or chemically generated anti-apoptotic free radical nitric oxide. Finally, 6-hydroxydopamine activated extracellular signal-regulated kinase in astrocytes and selective inhibitor of extracellular signal-regulated kinase activation partially prevented astrocyte death. Taken together, these data indicate that 6-hydroxydopamine-triggered oxidative stress induces extracellular signal-regulated kinase-dependent apoptotic death of astrocytes.

Iron protects astrocytes from 6-hydroxydopamine toxicity

The role of iron in 6-hydroxydopamine (6-OHDA) toxicity towards astrocytes was investigated in vitro using rat primary astrocytes, rat astrocytoma cell line C6, and human astrocytoma cell line U251. The assessment of mitochondrial respiration or lactate dehydrogenase release has shown a dose-dependent decrease in the viability of astrocytes treated with 6-OHDA, which coincided with DNA fragmentation and the changes in cellular morphology. This was a consequence of the oxidative stress mediated by 6-OHDA autoxidation products hydrogen peroxide, superoxide anion, and hydroxyl radical. Both FeSO(4) and FeCl(3) markedly alleviated detrimental effects of 6-OHDA treatment, while MgSO(4) was without effect. The protective action of iron was neutralized by a membrane-permeable iron chelator o-phenanthroline, which also augmented astrocyte killing in the absence of exogenous iron. The mechanisms responsible for iron-mediated protection of astrocytes did not involve interference with either 6-OHDA autoxidation, hydrogen peroxide toxicity, or 6-OHDA-induced activation of extracellular signal-regulated kinase. Finally, the addition of iron potentiated and its chelation blocked 6-OHDA toxicity towards neuronal PC12 cells, suggesting the opposite roles for this transition metal in regulating the survival of astrocytes and dopaminergic neurons.