Oxidative Stress and Inflammation in Chronic Kidney Disease: Role of Intravenous Iron and Vitamin D

Cardiovascular disease (CVD) is the leading cause of death among chronic kidney disease patients (CKD). The etiology of CVD in CKD is multifactorial and increasing evidence points to the important contribution of “nontraditional” risk factors including oxidative stress and inflammation. CKD is associated with a chronic imbalance of prooxidant and antioxidant factors that results in a state of chronic inflammation. Intravenous iron supplementation has been shown to induce oxidative stress and has been associated with lipid peroxidation and DNA damage. Conversely, treatment with vitamin D analogs has been associated with improved mortality in hemodialysis patients in 2 recent large cohort studies. These data suggest that vitamin D analogs may exert effects beyond their pharmacologic role in parathyroid hormone suppression. This article addresses the current data regarding the relative contributions of intravenous iron supplementation and vitamin D analog therapy on oxidative stress and inflammation in CKD patients.

Intravenous iron therapy in end-stage renal disease

Intravenous iron therapy is instrumental in the management of anemia in patients with end-stage renal disease (ESRD). Iron is available in several different preparations, with slight differences in the pharmacology of each. Given the importance of intravenous iron in the management of these patients, clinicians should be aware of the potential risks associated with it. Intravenous iron has effects on host immunity that raise concerns about clinical infection risk. Iron preparations appear to increase oxidative stress in these patients, which has important implications for cardiovascular disease states. Lastly, the effects of intravenous iron on liver disease are largely unknown.

Hepatocellular Damage Following Therapeutic Intravenous Iron Sucrose Infusion in a Child

The maximum tolerated single dose of intravenous iron infusion and iron pharmacokinetics are not known in children and not clear in adults. The case reported here is of a child given a large dose of intravenous iron sucrose (16 mg/kg) over 3 hours, who subsequently developed features of systemic iron toxicity. A TDM consultant discusses the case in the context of toxicokinetic analysis. Because the maximum tolerated dose and pharmacokinetics of intravenous iron preparations are not known, their use in both adults and children should still be undertaken with caution.

Transferrin saturation with intravenous irons: An in vitro study

BACKGROUND

Iron deficiency anemia in chronic kidney disease is commonly treated with one of three intravenous irons-iron dextran, iron sucrose, or iron gluconate. Substantial pharmacologic differences between drugs exist, but their ability to saturate transferrin has not been compared. Drugs that may lead to rapid transferrin saturation may lead to greater efficacy but also increased toxicity if transferring-mediated uptake of iron is the basis of this toxicity.

METHODS

We studied the in vitro ability of the three intravenous irons to donate iron to transferrin. Transferrin saturation was studied by direct visualization of the transferrin bands by urea polyacrylamide gel electrophoresis (PAGE), as well as a functional assay that evaluated the ability of iron to half saturate transferrin in a dose-dependent (0 to 100 microg/mL) and time-dependent (15 to 180 min) manner. Half-maximal dose (EC(50)) of iron needed to saturate transferrin was evaluated.

RESULTS

Nondextran irons were able to saturate transferrin in a dose-dependent and time-dependent manner. There was more rapid transferrin saturation with iron gluconate compared to iron sucrose. The slope of the EC(50) versus dose iron gluconate titration curve was -0.021 nmol/microg/mL (95% CI -0.025 to -0.017, P < 0.0001), for iron sucrose -0.006 nmol/microg/mL (95% CI -0.010 to -0.002, P= 0.002), and for iron dextran -0.001 nmol/microg/mL (95% CI -0.004 to 0.003, P > 0.2). The least square mean EC(50) computed for mean iron concentration was 5.95 nmol for iron gluconate (95% CI 5.82 to 6.08), 6.73 nmol for iron sucrose (95% CI 6.59 to 6.86), and 7.24 nmol for iron dextran (95% CI 7.11 to 7.38). Similar results were seen for the time-dependent transferrin saturation (drug x time interaction, F 6.0, P < 0.01). Urea PAGE analysis showed similar results as the functional assay.

CONCLUSION

Substantial heterogeneity in direct iron transfer from iron pharmaceuticals in vitro suggests that differences may exist in safety and efficacy of these drugs in vivo. In vivo studies are needed to compare the safety and efficacy of existing nondextran parenteral irons to better define the therapeutic ratio.

Intravenous iron and the risk of infection in end-stage renal disease patients

Oral iron is typically insufficient for the iron deficiency of hemodialysis patients. Intravenous (IV) iron is well tolerated by most patients and non-dextran-containing iron preparations are associated with few allergic reactions. However, there is the potential for an increased risk of infection with IV iron that appears to increase bacterial growth as well as inhibit the host's innate immune response to bacterial infection. Clinical studies suggest a link between iron therapy and infection. Practicing nephrologists should be aware of this issue, but should not hesitate to use IV iron in iron-deficient patients while avoiding the development of iron overload and administration of iron to patients who have active infection.

Effect of iron sucrose on human peritoneal mesothelial cells

BACKGROUND

Iron supplementation is often required in uraemic patients with anaemia. Peritoneal cavity was proposed as an alternative intravenous route for iron infusion in patients treated with peritoneal dialysis. We studied the effect of iron sucrose (Venofer) on the function of human peritoneal mesothelial cells maintained in in vitro culture.

MATERIALS AND METHODS

In in vitro experiments on human peritoneal, the mesothelial effect of elemental iron (in conc. 0.0001-1 mg mL-1) present in Venofer on their viability, growth and synthesis of IL-6 was studied. Additionally we evaluated with a fluorescent probe (2',7'-dichlorodihydro-fluorescein diacatate) generation of reactive oxygen species in cells exposed to iron sucrose. We also measured accumulation of iron in the cytoplasm of mesothelial cells after their in vitro exposure to Venofer.

RESULTS

In in vitro conditions iron induces a dose-dependent inhibition of viability of the mesothelial cells as reflected by inhibition of the cells growth by 34% at Fe 0.1 mg mL-1 vs. control (P < 0.05) increased release of lactate dehydrogenase (LDH) from the cytosol: 67.1 +/- 30.3 mU mL-1 at Fe 1 mg mL-1 vs. 7.9 +/- 6.4 in control group (P < 0.001), and reduced synthesis of IL-6: 209 +/- 378 pg mg-1 cell protein at Fe 1 mg mL-1 vs. 38674 +/- 4146 pg mg-1 cell protein in controls (P < 0.001). Cytotoxicity of iron towards mesothelial cells was enhanced in vitro when it was tested in presence of the dialysis fluid. Iron used in vitro at concentration 0.0001 mg mL-1 and greater induces generation of oxygen-derived free radicals in mesothelial cells. Furthermore, iron is taken by these cells and stored in their cytosol, resulting in stimulation of the intracellular generation of free radicals.

CONCLUSIONS

We conclude that iron used in the form of iron sucrose is cytotoxic to human peritoneal mesothelial cells. Accumulation of iron sucrose within cytoplasm of these cells may lead to induction of its chronic cytotoxic effect.

Iron sucrose: the oldest iron therapy becomes new

Several parenteral iron preparations are now available. This article focuses on iron sucrose, a hematinic, used more widely than any other for more than five decades, chiefly in Europe and now available in North America. Iron sucrose has an average molecular weight of 34 to 60 kd, and after intravenous (IV) administration, it distributes into a volume equal to that of plasma, with a terminal half-life of 5 to 6 hours. Transferrin and ferritin levels can be measured reliably 48 hours after IV administration of this agent. Iron sucrose carries no "black-box" warning, and a test dose is not required before it is administered. Doses of 100 mg can be administered over several minutes, and larger doses up to 300 mg can be administered within 60 minutes. The efficacy of iron sucrose has been shown in patients with chronic kidney disease (CKD) both before and after the initiation of dialysis therapy. Iron sucrose, like iron gluconate, has been associated with a markedly lower incidence of life-threatening anaphylactoid reactions and may be administered safely to those with previously documented intolerance to iron dextran or iron gluconate. Nonanaphylactoid reactions, including non-life-threatening hypotension, nausea, and exanthema, also are extremely uncommon with iron sucrose. Management of patients with the anemia of CKD mandates that we carefully examine the effectiveness and safety of this oldest of iron preparations and the accumulating present-day data regarding it and contemporaneous agents.

Parenteral iron formulations: a comparative toxicologic analysis and mechanisms of cell injury

BACKGROUND

Multiple parenteral iron (Fe) formulations exist for administration to patients with end-stage renal disease. Although there are concerns regarding their potential toxicities, no direct in vitro comparisons of these agents exist. Thus, the present study contrasted pro-oxidant and cytotoxic potentials of four available Fe preparations: Fe dextran (Fe dext), Fe sucrose (Fe sucr), Fe gluconate (Fe gluc), and Fe oligosaccharide (Fe OS).

METHODS

Differing dosages (0.06 to 1 mg/mL) of each compound were added to either (1) isolated mouse proximal tubule segments, (2) renal cortical homogenates, or (3) cultured human proximal tubule (HK-2) cells (0.5- to 72-hour incubations). Oxidant injury (malondialdehyde generation) and lethal cell injury (percentage of lactate dehydrogenase release; tetrazolium dye uptake) were assessed. Effects of selected antioxidants (glutathione [GSH], catalase, dimethylthiourea (DMTU), and sodium benzoate also were assessed.

RESULTS

Each test agent induced massive and similar degrees of lipid peroxidation. Nevertheless, marked differences in cell death resulted (Fe sucr >> Fe gluc > Fe dext approximately Fe OS). This relative toxicity profile also was observed in cultured aortic endothelial cells. Catalase, DMTU, and sodium benzoate conferred no protection. However, GSH and its constituent amino acid glycine blocked Fe sucr-mediated cell death. The latter was mediated by mitochondrial blockade, causing free radical generation and a severe adenosine triphosphate depletion state.

CONCLUSIONS

(1) parenteral Fes are highly potent pro-oxidants and capable of inducing tubular and endothelial cell death, (2) markedly different toxicity profiles exist among these agents, and (3) GSH can exert protective effects. However, the latter stems from GSH's glycine content, rather than from a direct antioxidant effect.

Catalytically active iron and bacterial growth in serum of haemodialysis patients after i.v. iron-saccharate administration

BACKGROUND

I.v. iron is commonly administered to haemodialysis patients suffering from anaemia to improve their response to erythropoietin therapy. It has been unclear whether routinely used doses of i.v. iron preparations could result in iron release into plasma in amounts exceeding the iron binding capacity of transferrin. Here, we have studied the effect of 100 mg of iron saccharate given as an i.v. injection on transferrin saturation and the appearance of potentially harmful catalytically active iron.

METHODS

We followed serum iron, transferrin and transferrin-saturation before and 5-210 min after administration of iron saccharate in 12 patients on chronic haemodialysis due to end-stage renal disease. We measured catalytically active iron by the bleomycin-detectable iron (BDI) assay and transferrin iron forms by urea gel electrophoresis, and studied iron-dependent growth of Staphylococcus epidermidis inoculated into the serum samples in vitro.

RESULTS

The iron saccharate injection resulted in full transferrin saturation and appearance of BDI in the serum in seven out of the 12 patients. BDI appeared more often in patients with a low serum transferrin concentration, but it was not possible to identify patients at risk based on serum transferrin or ferritin level before i.v. iron. The average transferrin saturation and BDI level increased until the end of the follow-up time of 3.5 h. The appearance of BDI resulted in loss of the ability of patient serum to resist the growth of S. epidermidis, which was restored by adding iron-free apotransferrin to the serum. Iron saccharate, added to serum in vitro, released only little iron and promoted only slow bacterial growth, but caused falsely high transferrin saturation by one routinely used serum iron assay.

CONCLUSIONS

The results indicate that 100 mg of iron saccharate often leads to transferrin oversaturation and the presence of catalytically active iron within 3.5 h after i.v. injection. As catalytically active iron is potentially toxic and may promote bacterial growth, it may be recommendable to use dosage regimens for i.v. iron that would not cause transferrin oversaturation.

The comparative safety of intravenous iron dextran, iron saccharate, and sodium ferric gluconate

Intravenous iron treatment is an important component of anemia therapy for patients on dialysis. Until recently iron dextran was the only parenteral form of iron available in the United States. This drug has been associated with occasional serious adverse reactions, including full-blown anaphylaxis. In 1999 the Food and Drug Administration approved a second form of iron for intravenous administration, sodium ferric gluconate in sucrose. It is expected that by the time of this publication, a third agent, iron saccharate will also be approved. In this review the comparative safety of these three agents is critically evaluated.