Appearance Of Non-transferrin-bound Iron Research Articles

Myelodysplastic Syndromes Benefit from Iron-Restricted Bone Marrow Transplant in Preclinical Mouse Model

Background: Hematopoietic stem cell transplantation (HSCT) remains the only fully curative therapy for diseases such as b-thalassemia, sickle cell disease, MDS and AML and represents a relevant procedure for gene therapy .Tissue iron overload and non-transferrin bound iron (NTBI) have emerged as adverse prognostic factors for post-transplant survival. Recently, we showed that - in line with observations in transplanted individuals - preparatory chemotherapy conditioning with a combination of busulfan and fludarabine in wild-type mice resulted in elevated serum iron and transferrin (Tf) saturation and elicited NTBI formation. Tf saturation and NTBI levels increased proportionally with conditioning intensity. Interestingly, we found that pre-conditioning TMPRSS6 silencing through a GalNAc-conjugated siRNA - by increasing hepcidin levels - reduced the peri-transplant elevation of Tf saturation and limited the appearance of NTBI. These results proved that NTBI formation is induced by conditioning chemotherapy in the peri-trasplant period independently of the presence of pre-existing iron overload. Aims & Methods: Here we asked whether these observations hold true in conditions hallmarked by pre-existing iron overload and elevated NTBI and how iron restriction impacts on bone marrow transplant (BMT) outcome. To this aim, we applied the GalNAc TMPRSS6 siRNA as iron restriction strategy in a mouse model of myelodysplastic syndromes (MDS) and assessed its ability to reduce conditioning-elicited NTBI formation as well as its potential benefit on BMT. After TMPRSS6 siRNA administration, CD45.2 + MDS mice received conditioning chemotherapy and transplant of CD45.1 + wild-type bone marrow cells. Systemic iron parameters, engraftment and chimerism were then analyzed. Results: Importantly, conditioning exacerbated the elevated systemic iron levels in MDS mice, which was prevented by pre-conditioning TMPRSS6 silencing. Similar to our observation in wild-type mice, recipient CD45.2 + MDS mice showed a superior blood chimerism, resulting from increased bone marrow and spleen engraftment of CD45.1 + donor cells. Multilineage engraftment in bone marrow, spleen and peripheral blood was superior in iron-restricted recipient MDS mice compared to controls. Finally, donor chimerism of hematopoietic stem and progenitor cells (HSPCs) was higher in iron-restricted versus control MDS mice undergoing BMT. Conclusion: These findings demonstrate that pre-transplant conditioning profoundly alters iron homeostasis and restricting iron improves BMT outcome by increasing engraftment efficiency. Overall, these data suggest that conditioning-elicited NTBI is a critical mediator of peri-transplant toxicity and adversely impacts transplant outcome. Specifically, our observations prove that iron restriction improves donor HSPC engraftment in the recipient bone marrow, likely resulting in more efficient reconstitution of the HSPC pool and improved multilineage engraftment. Lastly, our results indicate that the peri-transplant application of novel iron restriction strategies aimed at reducing conditioning-induced NTBI - by positively affecting BMT outcome - is of potential benefit for patients undergoing BMT or gene therapy, presenting either with or without pre-transplant iron overload.

Differences in circulating non-transferrin-bound iron after oral administration of ferrous sulfate, sodium iron EDTA, or iron polymaltose in women with marginal iron stores

Background. The adverse interactions between iron supplements and malaria have driven the assessment of new therapeutic options for anemia prophylaxis in areas holoendemic for falciparum malaria.Objective. To determine the responses of circulating non-transferrin-bound iron (NTBI) and plasma iron to three different oral iron compounds – ferrous sulfate, sodium iron ethylenediaminetetraacetate (NaFeEDTA), and iron polymaltose (IPM) – in women with marginal iron stores.Methods. Serum samples from 10 Guatemalan women with marginal iron stores were collected every 90 minutes over a period of 270 minutes, after the individually randomized administration of 100 mg of iron from each of the three studied iron compounds or water alone. Serum iron concentration was quantified by the ferrozine method, and circulating NTBI concentration was determined with a fluorometric competitive binding assay. Kinetic responses and maximal cumulative changes in serum concentrations of iron and NTBI were compared between the four treatments. Comparison was made with data from the same protocol in iron-adequate men.Conclusions. The administration of the two “slow-release” iron compounds, NaFeEDTA and IPM, resulted in a highly significant suppression of the appearance of NTBI in the circulation in the postsupplement period. These two bioavailable forms of iron supplement could represent a safe option for supplementation in malarial areas. The slope of the iron – NTBI relationship is steeper in men than in women.

Non transferrin bound iron (NTBI) in acute leukemias throughout conventional intensive chemotherapy: Kinetics of its appearance and potential predictive role in infectious complications

We analyzed appearance of non transferrin bound iron (NTBI) in 30 transplant eligible patients with acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) during conventional chemotherapy treatment program and evaluated possible relationship with transfusional body iron intake, iron parameters and clinical complications. For each course, serum samples for NTBI detection were taken prior to chemotherapy, during treatment and during subsequent bone marrow myelosuppression: NTBI was assessed by HPLC. Appearance of NTBI was observed from the start of induction treatment and was still detectable during bone marrow myelosuppression; the recovery of the bone marrow function coincided with the disappearance of NTBI. This kinetic was observed in all subsequent high doses chemotherapy courses, independently from confounding variables such as transfusional iron intake and transferrin saturation. NTBI seems to be a consequence of chemotherapy induced lysis of bone marrow cells and, partly, of hepatocytes after cytotoxic injury. The subsequent persistence of NTBI throughout bone marrow myelosuppression is related to the transient suspension of erythropoietic activity. Moreover, NTBI levels >2μM at the beginning of iatrogenic myelosuppression were associated with higher risk of sepsis caused by Gram negative Bacilli (RR 2.571), also compared with other infectious complications (RR 1.954).

Differences in Circulating Non-Transferrin-Bound Iron after Oral Administration of Ferrous Sulfate, Sodium Iron EDTA, or Iron Polymaltose in Women with Marginal Iron Stores

The adverse interactions between iron supplements and malaria have driven the assessment of new therapeutic options for anemia prophylaxis in areas holoendemic for falciparum malaria. To determine the responses of circulating non-transferrin-bound iron (NTBI) and plasma iron to three different oral iron compounds--ferrous sulfate, sodium iron ethylenediaminetetraacetate (NaFeEDTA), and iron polymaltose (IPM)--in women with marginal iron stores. Serum samples from 10 Guatemalan women with marginal iron stores were collected every 90 minutes over a period of 270 minutes, after the individually randomized administration of 100 mg of iron from each of the three studied iron compounds or water alone. Serum iron concentration was quantified by the ferrozine method, and circulating NTBI concentration was determined with a fluorometric competitive binding assay. Kinetic responses and maximal cumulative changes in serum concentrations of iron and NTBI were compared between the four treatments. Comparison was made with data from the same protocol in iron-adequate men. The serum iron and NTBI responses to ferrous sulfate were significantly greater than those to water and the other two iron compounds. Serum iron responses to IPM did not differ from those to water alone. The administration of the two "slow-release" iron compounds, NaFeEDTA and IPM, resulted in a highly significant suppression of the appearance of NTBI in the circulation in the postsupplement period. These two bioavailable forms of iron supplement could represent a safe option for supplementation in malarial areas. The slope of the iron-NTBI relationship is steeper in men than in women.

Non‐transferrin‐bound iron in haematological patients during chemotherapy and conditioning for autologous stem cell transplantation

Free iron induced hydroxyl radical formation is one possible mechanism for tissue injury during cytotoxic therapy. We studied the appearance of free, non-transferrin-bound iron (NTBI) at baseline and during the 20-d period after the onset of cytotoxic chemotherapy in patients with haematological malignancy undergoing intensive chemotherapy or conditioning for autologous stem cell transplantation (aSCT). NTBI was detected on average for 15.6 d in patients treated with chemotherapy only, and for 6.1 d in patients undergoing aSCT. The recovery of the bone marrow function coincided with the disappearance of NTBI. The type of the conditioning regimen was also associated with the appearance of NTBI. The timing of the presence of NTBI accords with the presence of the most important non-infectious complication of intensive chemotherapy and autologous transplantation, mucosal injury, and free iron is likely to contribute to this and probably other complications of the intensive treatments.

Effect of Repeated Apotransferrin Administrations on Serum Iron Parameters in Patients Undergoing Myeloablative Conditioning and Allogeneic Stem Cell Transplantation.

The myeloablative preconditioning for hematopoietic stem cell transplantation (SCT) disrupts the main route of body iron turnover by temporarily halting erythropoiesis. This is followed by rapid increase in transferrin saturation and appearance of non-transferrin-bound iron (NTBI) in plasma (Sahlstedt et al, Br J Haematol 2001). We have previously shown that considerable amounts of iron can in this situation be bound by a single intravenous dose of human plasma-derived ironless transferrin, apotransferrin (Sahlstedt al, Br J Haematol 2002). NTBI is cleared from circulation by the liver, to which iron-catalyzed generation of reactive oxygen species are considered to be potentially toxic as also possibly contributing to mucositis and idiopathic pneumonia syndrome. We studied the ability of three repeated apotransferrin dosing regimens to maintain the accumulating iron in a transferrin-bound form in 20 patients receiving cyclophosphamide 120mg/kg and total body irradiation 12 Gy before SCT. The low-dose group received a total dose (including loading and maintenance doses) of 340 mg/kg, the medium-dose group 610 mg/kg and the high-dose group 1040 mg/kg starting on day −6 before SCT. Serum transferrin, total iron, NTBI and transferrin saturation were analyzed from daily samples until day +14. A significantly higher increase in serum transferrin and in serum total iron was detected in the high-dose group compared with the other dose groups and controls. On the second day after start of preconditioning, the mean increase in serum iron was 48 μmol. At the same time, the 24-hour increment in serum transferrin after the apotransferrin doses decreased by 45% pointing to uptake of transferrin-bound iron by tissues. Serum iron levels remained significantly more elevated in the high-dose group compared with controls for about 10 days, after which their decrease coincided with appearance of reticulocytes in peripheral blood. In 5/8 patients in the high-dose group, no detectable NTBI was found during the study period, whereas in the controls 75% of the samples were NBTI positive. In conclusion, even with repeated administration of relatively large doses of apotransferrin, full transferrin saturation and appearance of NTBI can be prevented in only part of the patients. Achieving complete iron binding with apotransferrin in all SCT patients would apparently require very high apotransferrin doses. The remarkable rise in transferrin saturation indicates that about 180 μmol or iron per day is initially released into circulation after start of preconditioning therapy. [Display omitted]

Effect of repeated apotransferrin administrations on serum iron parameters in patients undergoing myeloablative conditioning and allogeneic stem cell transplantation

Myeloablative conditioning prior to allogeneic stem cell transplantation causes a rapid increase in transferrin saturation and potentially toxic non-transferrin-bound iron (NTBI) in plasma. We have studied the ability of repeatedly administered apotransferrin to maintain this iron in a transferrin-bound form. Twenty adult patients undergoing myeloablative conditioning and allogeneic stem cell transplantation were enrolled to receive apotransferrin with one of three dosage regimens. Ten consecutive patients with the same preconditioning were studied as controls. At the highest dose level, full transferrin saturation and appearance of NTBI were prevented in five of the eight patients. Serum iron increased significantly more in the patients receiving apotransferrin than in the controls and remained elevated until erythropoietic recovery. From the increment of iron saturation and the amount of endogenous and administered apotransferrin, an average 180 mumol of iron per day was bound to transferrin during the first 4 d after the start of the conditioning therapy. Thereafter, iron accumulation levelled off in most patients. The results suggested that about half of the amount of iron normally transported to erythropoiesis was initially released to plasma after induction of the erythroid arrest. Complete iron binding with apotransferrin would apparently require very high apotransferrin doses.

Bicarbonate inhibits the growth of Staphylococcus epidermidis in platelet concentrates by lowering the level of non‐transferrin‐bound iron

Platelet concentrates (PCs) contain non-transferrin-bound iron (NTBI) owing to the displacement of iron from plasma-derived transferrin by citrate. NTBI in the PC medium supports the growth of Staphylococcus epidermidis. The possibilities of lowering the level of NTBI have been studied with the aim to inhibit the growth of S. epidermidis in the PC medium. NTBI in PC supernatants was determined by a chelation method and by the bleomycin-detectable iron assay. Iron binding by transferrin was determined by spectrophotometry. The growth of inoculated S. epidermidis in PC supernatants was monitored by optical density and determination of viable counts. Bicarbonate enhanced in a dose-dependent manner transferrin iron binding in citrate-containing solutions, including citrated plasma and PAS-II. The use of a modified anticoagulant supplemented with bicarbonate effectively lowered the level of NTBI and inhibited bacterial growth in citrated plasma. Supplementation of bicarbonate to the additive solution to increase the ratio of bicarbonate to citrate in a reconstituted PC medium further inhibited bacterial growth. Maintenance of stable pH and bicarbonate level in the reconstituted medium necessitated storage under 5 percent CO(2). The relatively low bicarbonate level in PC medium promotes iron displacement by citrate from plasma-derived transferrin. The appearance of NTBI can be decreased and iron-dependent bacterial growth can be inhibited by increasing bicarbonate level in citrated plasma and PC medium. To achieve the same beneficial effect in blood banking, other more practical ways to bind NTBI in a harmless form should be developed.

Non-transferrin-bound iron during allogeneic stem cell transplantation.

Hydroxyl radical formation catalysed by non-transferrin-bound iron (NTBI) might contribute to transplantation-related complications. The occurrence of NTBI in 10 adult allogeneic stem cell transplantation (SCT) patients was followed for 20 d. The transferrin saturation reached 99% on d -4 and remained > 80% thereafter. NTBI, measured as bleomycin-detectable iron, was detected for 6-18 d in all patients with a peak on d -4. High transferrin saturation levels were associated with the appearance of NTBI with a threshold at 80% saturation. Prevention of the potential deleterious effects of NTBI might reduce transplantation-related morbidity.