Polynuclear iron complexes impair the function of polymorphonuclear granulocytes

Can Targeting Iron Help in Combating Chronic Pseudomonas Infection? A Systematic Review

Cystic fibrosis is an autosomal recessive disorder caused by a mutation in genes for cystic fibrosis transmembrane conductance regulator (CFTR) protein. CFTR gene is responsible for the production of sweat, digestive fluids, and mucus, and any mutation in this would lead to the thickening of these secretions. Cystic fibrosis is a multi-organ disorder, but 80% of patients suffer from respiratory problems due to chronic infections most commonly caused by Pseudomonas aeruginosa (P. aeruginosa). Eradication of these infections has become a challenge as P. aeruginosa has developed resistance to multiple antibiotics. In several studies, iron has been shown to play an integral role in biofilm formation, which is the predominant resistance mechanism used by P. aeruginosa to combat antibiotics. The increased iron content in cystic fibrosis patients' sputum samples explains their increased susceptibility to Pseudomonas infections. Hence in this review article, we have used the research data available on therapeutic agents that target iron as an adjuvant treatment for chronic Pseudomonas infection. We systematically screened three databases using focused words and Medical Subject Headings (MeSH) terms for relevant articles. Further, we applied the inclusion and exclusion criteria and performed a thorough quality appraisal. Thirty shortlisted relevant studies were meticulously reviewed. In our opinion, novel therapeutic approaches targeting iron such as iron chelators, gallium, and cefiderocol have potent anti-biofilm properties. Future studies and clinical trials using these approaches in the management of chronic Pseudomonas infection might help in decreasing morbidity and mortality in patients with cystic fibrosis. Exploring these approaches might also help to combat other resistant organisms whose survival is dependent on iron.

Impact of iron sucrose therapy on leucocyte surface molecules and reactive oxygen species in haemodialysis patients

BACKGROUND

It has been suggested that iron increases oxidative stress and that an excess of iron contributes to cardiovascular disease and infections in haemodialysis patients. In the present study, the effects of parenterally administered iron on leucocyte surface molecule expression and the production of reactive oxygen species (ROS) were evaluated.

METHODS

Ten chronic haemodialysis (HD) patients without iron overload were studied. To each patient, four different regimens were applied: placebo; iron sucrose, either 30 or 100 mg, administered via the outflow dialyser line; and 100 mg of iron sucrose infused via the inflow dialyser line. Blood was sampled at different time points: before, during and after infusion and immediately before the next dialysis session. Levels of CD11b and CD45 expression on granulocytes and of CD11b, CD14 and CD36 on monocytes were determined using flow cytometric analysis. The generation of ROS was quantified using chemiluminescence with and without ex vivo stimulation by phorbol myristate acetate (PMA).

RESULTS

No significant differences among the four different treatment regimes were found, neither in chemilumescence activity nor in the expression of CD11b and CD45 on granulocytes, and of CD11b, CD14 and CD36 on monocytes.

CONCLUSIONS

Our results suggest that parenteral infusion of iron sucrose during haemodialysis in patients who have no signs of iron overload has no significant effect on the expression of leucocyte surface molecules and does not increase production of ROS.

High-dose parenteral iron sucrose depresses neutrophil intracellular killing capacity

BACKGROUND

Iron is essential for the formation of hemoglobin. During long-term treatment with human recombinant erythropoietin (rhEPO), the majority of end-stage renal disease (ESRD) patients will not respond adequately to rhEPO unless substituted with intravenous iron. However, concern exists about possible detrimental effects of parenteral iron on cellular host defense and iron-mediated increments of oxidative stress.

METHODS

We analyzed phagocytic functions of polymorphonuclear leukocytes (PMN) isolated from 20 ESRD patients on peritoneal dialysis in response to 300 mg of iron sucrose or placebo administered intravenously over two hours in a randomized, double-blind manner. We evaluated Fc gamma R-dependent phagocytosis and killing (primary outcome variable) of opsonized Escherichia coli, Fc gamma R-dependent oxidative burst capacity, and complement receptor 3 (CR3, Mac1, CD11b/CD18)/tumor necrosis factor alpha (TNFalpha)-mediated release of bactericidal lactoferrin before, during, one hour, and two days after administration.

RESULTS

The absolute count and the percentage of E. coli killed by PMN of iron sucrose-treated peritoneal dialysis patients decreased significantly over time in comparison to placebo-treated patients (F = 3.48, df = 4, P = 0.008; F = 3.99, df = 4, P = 0.006, respectively). All secondary outcome variables were not different between both groups over time.

CONCLUSIONS

Killing capacity of PMN isolated from ESRD patients decreases in response to high-dose parenteral iron sucrose, possibly in part explaining reported higher hospitalization rates and lower survival rates of dialysis patients receiving frequent and high-dose parenteral iron.

Iron and infection

Intravenous iron therapy maintains iron stores and decreases erythropoietin demand in patients undergoing regular dialysis therapy. Microbiology studies show a close relationship between the availability of iron and bacterial virulence. Iron is also an essential requirement of bacteria for multiplication in the host. Therefore, clinical conditions associated with iron excess in the host may increase the risk for infection. Parenteral iron has already been shown in human and animal studies to be harmful when administered during infection. There is now convincing evidence that hydroxyl radicals, produced either by the Fenton reaction or by the iron-catalyzed Haber-Weiss reaction, are species responsible for the damaging effects of iron. The unavailability of iron limits microbial growth but also impairs host resistance. In end-stage renal disease, patients' overtreatment with iron enhances the pre-existing risk for infectious complications caused by dialysis procedure per se, malnutrition, increased intracellular calcium, as well as low and high molecular weight uremic toxins. Intravenous iron therapy may not only adversely affect phagocytes in end-stage renal disease patients, but also T and B lymphocytes.

Differential effects of iron load on basal and interferon-gamma plus lipopolysaccharide enhance anticryptococcal activity by the murine microglial cell line BV-2

Here we evaluated the influence of intracellular iron levels on the constitutive and interferon (IFN)-gamma plus lipopolysaccharide (LPS) enhanced anticryptococcal activity by the murine microglial cell line BV-2. We demonstrated that iron loading via ferric nitrilotriacetate (FeNTA) resulted in a significant increase in the constitutive levels of anticryptococcal activity, while the enhancing effects by IFN-gamma plus LPS were prevented. Accordingly, a major increase was observed in the levels of thiobarbituric reactive substance (TBARS) produced upon iron loading under basal conditions, whereas IFN-gamma plus LPS treatment, that per se did not affect TBARS production, prevented by about 50% the enhancement otherwise occurring in response to iron loading. The potential involvement of multiple effector system and their relation to intracellular iron will be discussed.

Impaired neutrophil chemotaxis in patients with thalassaemia major

Random and directed migration, O2- production, degranulation and adhesion were studied in neutrophils obtained from patients with homozygous beta-thalassaemia and iron overload, in the presence or absence of thalassaemic serum. The only significant defect found was an impairment in directed chemotaxis, further depressed after addition of thalassaemic serum. The chemotactic defect was encountered in all the patients that have suffered from pyogenic infections except one, and was not correlated with the severity of the iron overload. It is suggested that the described neutrophil migration impairment may contribute to the tendency towards infection in certain patients with homozygous beta-thalassaemia.

Neutrophils from patients with secondary haemosiderosis contain excessive amounts of autotoxic iron

Secondary haemosiderosis may be accompanied by a decrease in the phagocytic function of neutrophils (PMNs). This dysfunction has been attributed to an exaggerated generation of oxidants induced by intracellular iron. However, an accumulation of iron has so far not been reliably demonstrated in neutrophils harvested from iron-overloaded patients. Six polytransfused haemodialysed patients, with a serum ferritin level higher than 1000 micrograms/l, and 10 healthy controls were investigated. The iron status of PMNs was evaluated by iron determination using atomic absorption spectrometry and by ferritin measurement using radioimmunoassay. The phagocytic performance was measured by cytofluorometry. The results confirm that PMNs from the haemosiderosis patients have a decreased phagocytosis. Moreover, they demonstrate for the first time that these PMNs have an increased cellular iron and ferritin content. Both latter concentrations were 4 to 5 times more elevated in secondary haemosiderosis than in healthy controls. This iron accumulation may be toxic for the PMNs and may, at least partially, explain the three-fold higher risk of bacteraemia which has been reported in those patients.

Yersinia infections in patients with homozygous beta-thalassemia associated with iron overload and its treatment

Patients with homozygous beta-thalassemia are at increased risk of serious infections. Yersinia enterocolitica is an organism with a predilection for these and other iron-overloaded patients. Three young adult patients with beta-thalassemia who were chronically transfused and developed yersiniosis are reported. Iron overload and desferrioxamine use are predisposing factors, as supported by clinical, animal, and in vitro data. Iron excess both immunologically compromises the host and greatly enhances yersinial growth. Desferrioxamine may make host iron even more bioavailable to Yersinia. Recognition of this association and unusual manifestations in these patients such as an appendicitis-like syndrome may direct clinicians to earlier antiyersinial therapy and temporary cessation of chelation.

Bacterial iron enhances oxygen radical-mediated killing of Staphylococcus aureus by phagocytes

It has been shown that increasing bacterial iron concentration enhances killing by hydrogen peroxide (H2O2) but not by polymorphonuclear granulocytes (PMN). It is possible that owing to the multiple bactericidal mechanisms of the PMN, differences in the killing rate of iron-loaded bacteria and control bacteria are obscured. We decided, therefore, to compare the killing of iron-loaded bacteria with that of control bacteria using human monocytes (MN), PMN, and PMN-derived cytoplasts. Incubation of Staphylococcus aureus with increasing concentrations of ferrous ammonium sulfate (0 to 1,000 microM) progressively increased the iron content in the bacteria (from 0.01 to 0.24 mumol of iron per 10(9) bacteria). Iron loading of the bacteria markedly increased their susceptibility to killing by H2O2. After 1 h of incubation with 1 mM H2O2, 95 +/- 2% of the iron-loaded bacteria were killed compared with 18 +/- 4% of the control bacteria (P less than 0.0001). Iron loading of bacteria did not alter their susceptibility to killing by human PMN. However, iron-loaded bacteria were more susceptible to killing by MN (after 12 min of incubation, 81 +/- 2 versus 74 +/- 2% killing; P less than 0.008) and to killing by PMN-derived cytoplasts (after 60 min of incubation, 52 +/- 8 versus 33 +/- 5%; P = 0.003) than the controls. Moreover, iron loading enhanced luminol-mediated chemiluminescence of MN, PMN, and PMN-derived cytoplasts. The hydroxyl radical scavenger thiourea inhibited H2O2-mediated killing of iron-loaded staphylococci as well as luminol-mediated chemiluminescence. These results suggest that alterations in intrinsic iron content increase killing of staphylococci by H2O2, MN, and PMN-derived cytoplasts by a free radical-mediated mechanism.

Lipid peroxidation of human granulocytes (PMN) and monocytes by iron complexes

Because the phagocytic function of non-stimulated human polymorphonuclear granulocytes (PMN) is impaired after incubation with either polynuclear Fe(III) or Fe(II), we decided to study lipid peroxidation of PMN and monocytes by these iron complexes. Lipid peroxidation was assessed by measuring thiobarbituric acid reactive substances and fluorescent compounds. In this study we report that monocytes, isolated in the standard way (EDTA-mediated detachment), release significantly more thiobarbituric acid reactive substances after incubation with iron than PMN. Monocytes, however, isolated without EDTA release the same amount after incubation with iron as PMN. The iron complexes shown to impair phagocyte function also stimulated the peroxidation of membrane lipids. Ascorbic acid in high concentrations enhanced iron-induced lipid peroxidation. Lipid peroxidation induced by ferrous ascorbate (1:20) could be inhibited by catalase, the iron chelators deferoxamine and transferrin, and the hydroxyl radical scavenger thiourea. Mononuclear complexes (ferric citrate 1:20) did not impair granulocyte function and did not induce lipid peroxidation. Our results suggest that impaired phagocyte function in patients with iron overload may be due to non-transferrin bound iron-mediated peroxidation of membrane lipids. However, the lowest amount of ferrous ascorbate (1:20) capable of inducing lipid peroxidation (50 microM) was significantly higher than that which impaired phagocyte function (10 microM).

Effect of iron on polymorphonuclear granulocyte phagocytic capacity: role of oxidation state and effect of ascorbic acid

It has been shown that iron (III) impairs the function of polymorphonuclear granulocytes (PMN). We have studied the effect of iron (II), on the membrane function of PMN, by assessing the uptake of radiolabelled Staphylococcus aureus by these cells. Iron (II), significantly impaired PMN phagocytic function. Addition of ascorbic acid reduced uptake further. Ferrous ascorbate, molar ratio 1:20, impaired phagocytic capacity of PMN significantly at iron concentrations as low as 1-10 microM. The toxic effect of iron (II) was not observed when desferrioxamine or transferrin was present in the incubation medium. The oxygen-free radical scavengers thiourea, mannitol and catalase prevented toxicity mediated by ferrous ammoniumsulphate but not by ferrous ascorbate (molar ratio of 1:20). Although high concentrations of ascorbic acid inhibited the generation of .OH and also the formation of the DMPO-.OH adduct by zymosan stimulated PMN, toxicity of iron increased. Iron (II) impaired the uptake of S. aureus by PMN of a patient with chronic granulomatous disease while iron (III) did not. Iron mediated impairment of PMN function is not only a result of the generation of toxic oxygen metabolites but also of direct interaction of iron (II) or an iron (II)-oxygen intermediate with molecules of the cell membrane.