Non-transferrin-bound iron assay system utilizing a conventional automated analyzer

Investigation of biomarkers to predict outcomes in allogeneic hematopoietic stem cell transplantation

BACKGROUND

Various biomarkers have been developed and evaluated to predict the prognosis and complications of allogeneic hematopoietic cell transplantation (HCT). Most previous studies conducted on different biomarkers evaluated single effects such as those associated with inflammation, immunology, iron metabolism, and nutrition, and only a few studies have comprehensively analyzed markers.

OBJECTIVE

The study aimed to survey comprehensive multiple markers prior to HCT and extract those that significantly predict the outcomes.

STUDY DESIGN

A prospective multicenter observational study was performed. (UMIN000013506) Patients undergoing HCT for hematologic diseases were consecutively enrolled. Besides the usual clinical biomarkers, serum samples for extra-clinical biomarkers were collected and cryopreserved before starting the conditioning regimen. A total of 32 candidate biomarkers were selected, 23 from hematology, biochemistry, immunology, nutrition, and iron metabolism, and 9 from composite markers. Based on the area under the curve (AUC) values for survival, promising biomarkers was extracted. Internal validation for these markers was applied based on bootstrap methods. Setting the cut-off values for them, log-rank test was applied and outcomes including overall survival (OS), relapse, and non-relapse mortality (NRM) were evaluated using multivariate analyses. Furthermore, detailed analysis including transplant-related complications and external validation were conducted focusing on C-reactive protein (CRP) to platelet (Plt) ratio.

RESULTS

A total of 152 patients with hematologic malignancies were enrolled from April 2014 to March 2017. CRP, soluble interleukin-2 receptor (IL2R), CRP to albumin (Alb) ratio, CRP to Plt ratio, Plt to IL2R ratio, and IL2R to Alb ratio were identified as promising markers. Internal validation successfully confirmed their reliability of AUC and multivariate analysis demonstrated the statistical significance between the higher and the lower markers. Above all, a higher CRP to Plt ratio was significantly associated with a lower OS (hazard ratio [HR] 2.77; 95% confidence interval [CI] 1.30-5.91; P = 0.008) and higher non-relapse mortality rates (HR 2.79; 95%CI 1.14-6.80; P = 0.024) at 180 days. Furthermore, univariate analysis showed that a higher CRP to Plt ratio was significantly associated with a higher incidence of sinusoidal obstructive syndrome (P < 0.001) and bloodstream infection (P = 0.027). An external validation test confirmed the significance of the CRP to Plt ratio for these outcomes.

CONCLUSION

The multicenter prospective observational study successfully identified significant biomarkers in patients with hematologic malignancies who received HCT. In particular, CRP to Plt ratio was identified as a novel and useful biomarker for predicting transplant outcomes. Further investigations are needed to validate the novel markers, analysis of the pathophysiology, and application to treatment settings other than HCT.

Non-thermal plasma elicits ferrous chloride-catalyzed DMPO-OH

Non-thermal plasma (NTP) induces the generation of reactive oxygen species (ROS) and reactive nitrogen species, such as hydroxyl radicals (^•OH), hydrogen peroxide (H₂O₂), singlet oxygen, superoxide, ozone, and nitric oxide, at near-physiological temperatures. These molecules promote blood coagulation, wound healing, disinfection, and selective cancer cell death. Based on these evidences, clinical trials of NTP have been conducted for treating chronic wounds and head and neck cancers. Although clinical applications have progressed, the stoichiometric quantification of NTP-induced ROS remains unclear in the liquid phase in the presence of FeCl₂ or FeCl₃ in combination with biocompatible reducing agents, which may modulate the final biological effects of NTP. In this study, we employed electron paramagnetic resonance spectroscopy to quantify ROS using spin-trapping probe, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and H₂O₂, using luminescent probe in the presence of FeCl₂ or FeCl₃. NTP-induced DMPO-OH levels were elevated 10-100 µM FeCl₂ or 500 and 1000 µM FeCl₃. NTP-induced DMPO-OH with 10 µM FeCl₂ or FeCl₃ was significantly scavenged by ascorbate, α-tocopherol, dithiothreitol, reduced glutathione, or oxidized glutathione, whereas dehydroascorbate was ineffective in 2 mM DMPO. NTP-induced H₂O₂ was significantly degraded by 100 µM FeCl₂ and FeCl₃ in an iron-dependent manner. Meanwhile, decomposition of H₂O₂ by catalase decayed DMPO-OH efficiently in the presence of iron, indicating iron causes DMPO-OH production and degradation simultaneously. These results suggest that NTP-induced DMPO-OH is generated by the H₂O₂-consuming, iron-dependent Fenton reaction and ferryl intermediates. The potential iron-mediated ROS production by NTP is also discussed to clarify the interaction between NTP-induced ROS and biomolecules.

Iron-Induced Oxidative Stress in Human Diseases

Iron is responsible for the regulation of several cell functions. However, iron ions are catalytic and dangerous for cells, so the cells sequester such redox-active irons in the transport and storage proteins. In systemic iron overload and local pathological conditions, redox-active iron increases in the human body and induces oxidative stress through the formation of reactive oxygen species. Non-transferrin bound iron is a candidate for the redox-active iron in extracellular space. Cells take iron by the uptake machinery such as transferrin receptor and divalent metal transporter 1. These irons are delivered to places where they are needed by poly(rC)-binding proteins 1/2 and excess irons are stored in ferritin or released out of the cell by ferroportin 1. We can imagine transit iron pool in the cell from iron import to the export. Since the iron in the transit pool is another candidate for the redox-active iron, the size of the pool may be kept minimally. When a large amount of iron enters cells and overflows the capacity of iron binding proteins, the iron behaves as a redox-active iron in the cell. This review focuses on redox-active iron in extracellular and intracellular spaces through a biophysical and chemical point of view.

Labile iron, ROS, and cell death are prominently induced by haemin, but not by non-transferrin-bound iron

BACKGROUND

In transfusion-related iron overload, haem-derived iron accumulation in monocytes/macrophages is the initial event. When iron loading exceeds the ferritin storage capacity, iron is released into the plasma. When iron loading exceeds transferrin binding capacity, labile, non-transferrin-bound iron (NTBI) appears and causes organ injury. Haemin-induced cell death has already been investigated; however, whether NTBI induces cell death in monocytes/macrophages remains unclear.

MATERIAL AND METHODS

Human monocytic THP-1 cells were treated with haemin or NTBI, particularly ferric ammonium citrate (FAC) or ferrous ammonium sulfate (FAS). The intracellular labile iron pool (LIP) was measured using an iron-sensitive fluorescent probe. Ferritin expression was measured by western blotting.

RESULTS

LIP was elevated after haemin treatment but not after FAC or FAS treatment. Reactive oxygen species (ROS) generation and cell death induction were remarkable after haemin treatment but not after FAC or FAS treatment. Ferritin expression was not different between the FAC and haemin treatments. The combination of an iron chelator and a ferroptosis inhibitor significantly augmented the suppression of haemin cytotoxicity (p = 0.011).

DISCUSSION

The difference in LIP suggests the different iron traffic mechanisms for haem-derived iron and NTBI. The Combination of iron chelators and antioxidants is beneficial for iron overload therapy.

Zinc mediates the interaction between ceruloplasmin and apo-transferrin for the efficient transfer of Fe(III) ions

Fe(II) exported from cells is oxidized to Fe(III), possibly by a multi-copper ferroxidase (MCF) such as ceruloplasmin (CP), to efficiently bind with the plasma iron transport protein transferrin (TF). As unbound Fe(III) is highly insoluble and reactive, its release into the blood during the transfer from MCF to TF must be prevented. A likely mechanism for preventing the release of unbound Fe(III) is via direct interaction between MCF and TF; however, the occurrence of this phenomenon remains controversial. This study aimed to reveal the interaction between these proteins, possibly mediated by zinc. Using spectrophotometric, isothermal titration calorimetric, and surface plasmon resonance methods, we found that Zn(II)-bound CP bound to iron-free TF (apo-TF) with a Kd of 4.2 μM and a stoichiometry CP:TF of ∼2:1. Computational modeling of the complex between CP and apo-TF predicted that each of the three Zn(II) ions that bind to CP further binds to acidic amino acid residues of apo-TF to play a role as a cross-linker connecting both proteins. Domain 4 of one CP molecule and domain 6 of the other CP molecule fit tightly into the clefts in the N- and C-lobes of apo-TF, respectively. Upon the binding of two Fe(III) ions to apo-TF, the resulting diferric TF [Fe(III)2TF] dissociated from CP by conformational changes in TF. In human blood plasma, zinc deficiency reduced the production of Fe(III)2TF and concomitantly increased the production of non-TF-bound iron. Our findings suggest that zinc may be involved in the transfer of iron between CP and TF.

Analytical evaluation of serum non-transferrin-bound iron and its relationships with oxidative stress and cardiac load in the general population

Excessive iron accumulation provokes toxic effects, especially in the cardiovascular system. Under iron overload, labile free non-transferrin-bound iron (NTBI) can induce cardiovascular damage with increased oxidative stress. However, the significance of NTBI in individuals without iron overload and overt cardiovascular disease has not been investigated. We aimed to examine the distribution of serum NTBI and its relationship with oxidative stress and cardiac load under physiological conditions in the general population.We enrolled individuals undergoing an annual health check-up and measured serum NTBI and derivatives of reactive oxygen metabolites (d-ROM), an oxidative stress marker. In addition, we evaluated serum levels of B-type natriuretic peptide (BNP) to examine cardiac load. We excluded patients with anemia, renal dysfunction, cancer, active inflammatory disease, or a history of cardiovascular disease.A total of 1244 individuals (57.8 ± 11.8 years) were enrolled, all of whom had detectable serum NTBI. d-ROM and BNP showed significant trends across NTBI quartiles. Multivariable regression analysis revealed that serum iron and low-density lipoprotein cholesterol were positively associated with NTBI but that age, d-ROM, and BNP showed an inverse association with this measure. In logistic regression analysis, NTBI was independently associated with a combination of higher levels of both d-ROM and BNP than the upper quartiles after adjustment for possible confounding factors.Serum NTBI concentration is detectable in the general population and shows significant inverse associations with oxidative stress and cardiac load. These findings indicate that serum NTBI in physiological conditions does not necessarily reflect increased oxidative stress, in contrast to the implications of higher levels in states of iron overload or pathological conditions.

Curcuminoids supplementation ameliorates iron overload, oxidative stress, hypercoagulability, and inflammation in non-transfusion-dependent β-thalassemia/Hb E patients

Curcuminoids, polyphenol compounds in turmeric, possess several pharmacological properties including antioxidant, iron-chelating, and anti-inflammatory activities. Effects of curcuminoids in thalassemia patients have been explored in a limited number of studies using different doses of curcuminoids. The present study aims to evaluate the effects of 24-week curcuminoids supplementation at the dosage of 500 and 1000 mg/day on iron overload, oxidative stress, hypercoagulability, and inflammation in non-transfused β-thalassemia/Hb E patients. In general, both curcuminoids dosages significantly lowered the levels of oxidative stress, hypercoagulability, and inflammatory markers in the patients. In contrast, reductions in iron parameter levels were more remarkable in the 1000 mg/day group. Subgroup analysis revealed that a marker of hypercoagulability was significantly decreased only in patients with baseline ferritin ≤ 1000 ng/ml independently of curcuminoids dosage. Moreover, the alleviation of iron loading parameters was more remarkable in patients with baseline ferritin > 1000 ng/ml who receive 1000 mg/day curcuminoids. On the other hand, the responses of oxidative stress markers were higher with 500 mg/day curcuminoids regardless of baseline ferritin levels. Our study suggests that baseline ferritin levels should be considered in the supplementation of curcuminoids and the appropriate curcuminoids dosage might differ according to the required therapeutic effect. Thai Clinical Trials Registry (TCTR): TCTR20200731003; July 31, 2020 "retrospectively registered".

Iron

Iron deficiency anemia affects approximately one-third of the world's population, and about half the cases are due to iron deficiency. The latest research on iron metabolism published in original articles and systematic reviews is described, and references to recent reviews provided. The topics include dietary sources and bioavailability, iron homeostasis, functions of iron in the body, and biomarkers of status. The consequences of iron deficiency and excess are discussed, with particular focus on vulnerable populations such as pregnant women, infants and the elderly. The newest dietary recommendations, including dietary reference values and food based dietary guidelines, are briefly summarized, followed by the latest developments in food fortification and iron supplementation.

Characterisation of Lactoferrin Isolated from Acid Whey Using Pilot-Scale Monolithic Ion-Exchange Chromatography

The aim of this study was to characterize the properties of lactoferrin (LF) obtained in a process developed for its isolation from acid whey derived from the production of fresh curd cheese, using a unique technology of ion-exchange chromatography on CIM® monolithic columns. The freeze-dried lactoferrin samples produced on the pilot plant (capacity 1 m3) were examined for the purity, iron-binding capacity, antibacterial activity, and pH- and temperature-stability. Apo-LF inhibited several tested strains (enterobacteria, Staphylococcus, Streptococcus salivarius) except clostridia, lactic acid bacteria, and bifidobacteria. Sample of LF intentionally saturated with Fe3+ lost its antibacterial activity, indicating the involvement of mechanisms based on depriving bacteria of an iron source. All samples, regardless of the iron-saturation level, exhibited stability in pH range 4.0 to 11.0. LF with higher iron content (A-value = 41.9%) showed better thermal stability. Heat treatment up to 72 °C/3 s did not reduce antimicrobial activity against E. coli O157: H7 tox-. Higher purity (above 91%), higher iron-binding capacity and higher inhibitory activity against E. coli O157: H7 tox- compared to some similar products from the market was observed. These results demonstrate a high potential of monolithic ion-exchange chromatography for industrial processing of acid whey as a source of LF that can be used in new products with high-added value. The upscaling of the process is ongoing on a demonstration plant (10–30 m3/day capacity).

Novel automated measuring system for evaluating labile plasma iron in serum

Background

As the saturation of transferrin by iron in the serum is approximately 30%, iron loaded to the blood can bind to transferrin not bearing iron. Nevertheless, prolonged iron influx finally results in full transferrin saturation, and iron not bound to transferrin will appear in the serum; this iron is known as non-transferrin-bound iron (NTBI). NTBI damages organs through the production of free radicals. Previously, we established an automated quantification system for NTBI; however, measuring labile plasma iron, which is considered as a highly redox-active component of NTBI, should be a better prognostic factor in iron-overloaded patients.

Methods

We designed and developed a novel system for evaluating labile plasma iron utilizing the Trinder reaction. Automated system was utilized because the previously reported methods for labile plasma iron are intricate and the introduction to the clinical stage has been challenging. Validations such as the contribution of serum proteins and metal ions for this system were evaluated using human serum samples.

Results

We confirmed that our novel system can evaluate labile plasma iron utilizing Trinder reaction and the oxidative potential of ceruloplasmin in the serum. This system was also confirmed to be clinically practical. Metals other than iron did not influence this system. We observed that samples with high NTBI did not always exhibit high labile plasma iron and vice versa, highlighting the necessity of labile plasma iron quantification in evaluating the toxicity of NTBI.

Conclusions

Our novel system should contribute to fundamental and clinical research because it can measure labile plasma iron using the high-throughput automated analyser.

Laboratory methodologies for indicators of iron status: strengths, limitations, and analytical challenges

Biochemical assessment of iron status relies on serum-based indicators, such as serum ferritin (SF), transferrin saturation, and soluble transferrin receptor (sTfR), as well as erythrocyte protoporphyrin. These indicators present challenges for clinical practice and national nutrition surveys, and often iron status interpretation is based on the combination of several indicators. The diagnosis of iron deficiency (ID) through SF concentration, the most commonly used indicator, is complicated by concomitant inflammation. sTfR concentration is an indicator of functional ID that is not an acute-phase reactant, but challenges in its interpretation arise because of the lack of assay standardization, common reference ranges, and common cutoffs. It is unclear which indicators are best suited to assess excess iron status. The value of hepcidin, non-transferrin-bound iron, and reticulocyte indexes is being explored in research settings. Serum-based indicators are generally measured on fully automated clinical analyzers available in most hospitals. Although international reference materials have been available for years, the standardization of immunoassays is complicated by the heterogeneity of antibodies used and the absence of physicochemical reference methods to establish "true" concentrations. From 1988 to 2006, the assessment of iron status in NHANES was based on the multi-indicator ferritin model. However, the model did not indicate the severity of ID and produced categorical estimates. More recently, iron status assessment in NHANES has used the total body iron stores (TBI) model, in which the log ratio of sTfR to SF is assessed. Together, sTfR and SF concentrations cover the full range of iron status. The TBI model better predicts the absence of bone marrow iron than SF concentration alone, and TBI can be analyzed as a continuous variable. Additional consideration of methodologies, interpretation of indicators, and analytic standardization is important for further improvements in iron status assessment.

The Effects of Nutrition, Exercise, and a Praying Program on Reducing Iron Overload in Patients With Beta-Thalassemia Major: A Randomized Clinical Trial

BACKGROUND

Excessive iron accumulation in the visceral organs creates problems for patients with beta-thalassemia major. Despite chelation therapy, mortality rate from the complications of this disease is still quite high.

OBJECTIVES

This study aimed to investigate the effectiveness of nutrition, exercise, and a praying program at reducing iron overload in patients with beta-thalassemia major.

PATIENTS AND METHODS

This randomized clinical trial assessed the effect of the designed care program on iron overload. The study was conducted in 38 patients with beta-thalassemia major who ranged in age from 15 - 35 years and had been referred to the largest center for thalassemic patients in Shiraz. The patients were randomly assigned to an intervention (n = 18) and a control (n = 20) group. Blood samples were collected from the participants before and two months after the intervention. Then, the data were statistically analyzed using chi-square, Fisher's exact test, Mann-Whitney U-test, Wilcoxon, independent samples t-test, and paired samples t-test.

RESULTS

The results showed that the mean level of serum ferritin significantly decreased in the intervention group two months after beginning the intervention. Also, the mean level of serum iron decreased in the intervention group, but the difference was not statistically significant.

CONCLUSIONS

The planned educational program could be used to reduce iron overload and ultimately improve the patients' health status.

Chemical tools for detecting Fe ions

Owing to its distinctive electrochemical properties with interconvertible multiple oxidation states, iron plays a significant role in various physiologically important functions such as respiration, oxygen transport, energy production, and enzymatic reactions. This redox activity can also potentially produce cellular damage and death, and numerous diseases are related to iron overload resulting from the dysfunction of the iron regulatory system. In this case, “free iron” or “labile iron,” which refers to iron ion weakly bound or not bound to proteins, causes aberrant production of reactive oxygen species. With the aim of elucidating the variation of labile iron involved in pathological processes, some chemical tools that can qualitatively and/or quantitatively monitor iron have been utilized to investigate the distribution, accumulation, and flux of biological iron species. Since iron ions show unique reactivity depending on its redox state, i.e., Fe²⁺ or Fe³⁺ (or transiently higher oxidative states), methods for the separate detection of iron species with different redox states are preferred to understand its physiological and pathological roles more in detail. The scope of this review article covers from classical chromogenic to newly emerging chemical tools for the detection of Fe ions. In particular, chemical tools applicable to biological studies will be presented.

Clinical and methodological factors affecting non-transferrin-bound iron values using a novel fluorescent bead assay

Nontransferrin-bound iron (NTBI) is a heterogeneously speciated plasma iron, typically detectable when transferrin saturation (TfSat) exceeds 75%. Here, we examine factors affecting NTBI levels by a recently discovered direct chelator-based (CP851) fluorescent bead-linked flow-cytometric assay (bead-NTBI), compared with the established indirect nitrilotriacetate (NTA) assay in 122 iron-overloaded patients, including 64 on recent iron chelation therapy and 13 healthy volunteers. Both methods correlated (r = 0.57, P < 0.0001) but with low agreement, attributable to 2 major factors: (1) the NTA method, unlike the bead method, is highly dependent on TfSat, with NTBI under-estimation at low TfSat and over-estimation once Tf is saturated, (2) the bead method detects <3-fold higher values than the NTA assay in patients on recent deferiprone-containing chelation due to greater detection of chelate complexes but lower values for patients on deferasirox. The optimal timing of sample collection relative to chelation dosing requires further study. Patients with splenectomy, high-storage iron, and increased erythropoiesis had greater discrepancy between assays, consistent with differential access by both methods to the NTBI pools associated with these clinical variables. The bead-NTBI assay has advantages over the NTA assay, being less dependent on TfSat, hence of less tendency for false-negative or false-positive values at low and high TfSat, respectively.