Quantifying non-transferrin-bound iron (NTBI) in human plasma: incorporating BODIPY-pyridylhydrazone (BODIPY-PH) within a thin green film linked to a portable fluorescence-based device.

Free iron in human serum or non-transferrin-bound iron (NTBI) can generate free radicals and lead to oxidative damage. Moreover, it is highly toxic to various tissues and a vital biomarker related to the iron-loading status of thalassemia and Alzheimer's patients. In NTBI in healthy individuals, NTBI levels are typically less than 1 µM; current NTBI analysis usually requires advanced instrumentation and many-step sample pretreatment. To address this issue, we employed our invented BODIPY derivative, BODIPY-PH, as a fluorescence probe and trapped it onto the microcentrifuge tube lid using tapioca starch. The fluorescence intensity of BODIPY-PH increased with increasing NTBI concentration (turn-on). The developed portable reaction chamber facilitates rapid analysis (∼5 min) using small sample volumes (10 µL sample in a total volume of 600 µL). Under optimum conditions, using the sample-developed portable fluorescence device and fluorescence spectrometer, we achieved impressive limits of detection (LOD) of 0.003 and 0.0015 µM, respectively. Furthermore, the developed sensors show relatively high selectivity toward Fe3+ over other metal ions and biomolecules (i.e., Fe2+, Cr3+, Cu2+, and glucose). The sensor performance in serum samples of thalassemia patients exhibited no significant difference compared to the labeled value (obtained from standard methods). Overall, the developed fluorescence sensor is suitable for determining NTBI and offers high sensitivity, high selectivity, and a short incubation time (5 min). Moreover, the method requires a limited number of reagents, is simple to use, and uses low-cost equipment to determine NTBI in human serum samples.

Atherosclerosis is aggravated by iron overload and ameliorated by dietary and pharmacological iron restriction.

AIMS: Whether and how iron affects the progression of atherosclerosis remains highly debated. Here, we investigate susceptibility to atherosclerosis in a mouse model (ApoE-/- FPNwt/C326S), which develops the disease in the context of elevated non-transferrin bound serum iron (NTBI). METHODS AND RESULTS: Compared with normo-ferremic ApoE-/- mice, atherosclerosis is profoundly aggravated in iron-loaded ApoE-/- FPNwt/C326S mice, suggesting a pro-atherogenic role for iron. Iron heavily deposits in the arterial media layer, which correlates with plaque formation, vascular oxidative stress and dysfunction. Atherosclerosis is exacerbated by iron-triggered lipid profile alterations, vascular permeabilization, sustained endothelial activation, elevated pro-atherogenic inflammatory mediators, and reduced nitric oxide availability. NTBI causes iron overload, induces reactive oxygen species production and apoptosis in cultured vascular cells, and stimulates massive MCP-1-mediated monocyte recruitment, well-established mechanisms contributing to atherosclerosis. NTBI-mediated toxicity is prevented by transferrin- or chelator-mediated iron scavenging. Consistently, a low-iron diet and iron chelation therapy strongly improved the course of the disease in ApoE-/- FPNwt/C326S mice. Our results are corroborated by analyses of serum samples of haemochromatosis patients, which show an inverse correlation between the degree of iron depletion and hallmarks of endothelial dysfunction and inflammation. CONCLUSION: Our data demonstrate that NTBI-triggered iron overload aggravates atherosclerosis and unravel a causal link between NTBI and the progression of atherosclerotic lesions. Our findings support clinical applications of iron restriction in iron-loaded individuals to counteract iron-aggravated vascular dysfunction and atherosclerosis.

Impact of non-transferrin-bound iron (NTBI) in comparison to serum ferritin on outcome after allogeneic stem cell transplantation (ASCT).

The optimal parameters and time points for the measurement of iron overload (IO) in allogeneic stem cell transplantation (ASCT) patients are still under discussion. Hyperferritinemia and IO are poor prognostic factors in ASCT. We hypothesize that non-transferrin-bound iron (NBTI) is possibly a better marker to predict the effect of IO on the outcome than serum ferritin (SF), which however is not specific for IO. The aim of this prospective observational trial was to evaluate the influence of NBTI in comparison to SF on the outcome of ASCT patients [overall survival, bloodstream infections (BSIs), and invasive fungal infections (IFIs)]. We analyzed daily transferrin saturation (TSAT), SF, and NTBI (if TSAT exceeded 70%) in 100 patients who received ASCT during conditioning, and on day 0, +7, and +14 post-ASCT. After a median NTBI level of 0 µmol/l at baseline, the median of the area under the curve (AUC) of NTBI between conditioning and ASCT (d0) increased to 17 µmol*d/l, and between ASCT and day +14 to 56.3 µmol*d/l. Higher NTBI-AUC d0 resulted in a higher risk of BSI (HR 1.042, p = 0.009) and IFI (HR 1.070, p = 0.001) and showed a trend of inferior 1-year survival (65 vs. 76%, p = 0.09). Baseline SF did not influence BSI, but higher levels resulted in more IFI (HR 1.26, p < 0.001). In conclusion, NTBI possibly better predict for a higher risk of bloodstream infections than SF and needs further investigation.

Heart Rate Variability for Early Detection of Iron Overload Cardiomyopathy in ß-Thalassemia Patients.

Iron overload cardiomyopathy remains the major cause of death in ß-thalassemia (ß-thal). Conventional routine screening parameters such as serum ferritin and echocardiogram (ECG) do not permit early detection of this condition. Although non-transferrin-bound iron (NTBI) is a reliable indicator for iron overload, it is still not universally available. Recently, heart rate variability (HRV), representing cardiac autonomic function, was found to be depressed in thalassemia patients. We hypothesized that HRV can be used for early detection of iron overload cardiomyopathy. Fifty patients (aged 29 ± 11 years; 31 females and 19 males) with ß-thal were enrolled. The 24-hour Holter monitoring for HRV, serum ferritin, NTBI, hematological values and ECG were performed for each patient. Of the 50 patients, 29 carried ß-thal major (ß-TM). Non-transferrin-bound iron was weakly correlated to all time-domain HRV parameters. Low- and high-frequency domain HRV parameters were also inversely weakly correlated with NTBI. Neither HRV nor NTBI was correlated with serum ferritin. With its weak but significant correlation with NTBI, HRV may be considered to be used as a potential indicator of an iron overload condition and an early marker of cardiac involvement in patients with ß-thal.

Verapamil downregulates iron uptake and upregulates divalent metal transporter 1 expression in H9C2 cardiomyocytes.

Belgrade rats have a defect in divalent metal transport 1 (DMT1) with a reduced heart iron, indicating that DMT1 plays a physiological role in non-transferrin-bound iron (NTBI) uptake by cardiomyocytes. However, L-type voltage-dependent Ca2+ channel (LVDCC) blockers were recently demonstrated to significantly reduce NTBI uptake by cardiomyocytes, implying that LVDCC plays a dominant role in NTBI uptake by cardiomyocytes under iron-overloaded conditions. These findings led us to hypothesize that the LVDCC blocker-induced reduction in NTBI uptake might result not only from the inhibition of LVDCC-mediated NTBI uptake but also from the suppression of DMT1-mediated NTBI uptake. We therefore investigated the effects of the LVDCC blocker verapamil on NTBI uptake as well as DMT1 expression in H9C2 cells by the measurement of radio-labeled 55 Fe(II), reverse transcription polymerase chain reaction (RT-PCR) and western blot analysis. We demonstrated that verapamil induced a significant reduction in NTBI uptake by H9C2 cells but also unexpectedly a remarkable increase rather than decrease in the expression of DMT1 mRNA and protein in H9C2 cells. Our findings imply that the verapamil-induced reduction in NTBI uptake by H9C2 cells is not associated with DMT1 and also indicate that verapamil stimulates rather than inhibits DMT1 expression and DMT1-mediated iron uptake by heart cells.

Iron Absorption in Iron-Deficient Women, Who Received 65 mg Fe with an Indonesian Breakfast, Is Much Better from NaFe(III)EDTA than from Fe(II)SO4, with an Acceptable Increase of Plasma NTBI. A Randomized Clinical Trial.

Plasma non-transferrin-bound iron (NTBI) is potentially harmful due to the generation of free radicals that cause tissue damage in vascular and other diseases. Studies in iron-replete and iron-deficient subjects, receiving a single oral test dose of Fe(II)SO4 or NaFe(III)EDTA with water, revealed that FeSO4 was well absorbed when compared with NaFeEDTA, while only the Fe(II) compound showed a remarkable increase of NTBI. As NaFeEDTA is successfully used for food fortification, a double-blind randomized cross-over trial was conducted in 11 healthy women with uncomplicated iron deficiency. All subjects received a placebo, 6.5 mg FeSO4, 65 mg FeSO4, 6.5 mg NaFeEDTA, and 65 mg NaFeEDTA with a traditional Indonesian breakfast in one-week intervals. Blood tests were carried out every 60 min for five hours. NTBI detection was performed using the fluorescein-labeled apotransferrin method. Plasma iron values were highly increased after 65 mg NaFeEDTA, twice as high as after FeSO4. A similar pattern was seen for NTBI. After 6.5 mg of NaFeEDTA and FeSO4, NTBI was hardly detectable. NaFeEDTA was highly effective for the treatment of iron deficiency if given with a meal, inhibiting the formation of nonabsorbable Fe-complexes, while NTBI did not exceed the range of normal values for iron-replete subjects.

In vivo behavior of NTBI revealed by automated quantification system.

Non-Tf-bound iron (NTBI), which appears in serum in iron overload, is thought to contribute to organ damage; the monitoring of serum NTBI levels may therefore be clinically useful in iron-overloaded patients. However, NTBI quantification methods remain complex, limiting their use in clinical practice. To overcome the technical difficulties often encountered, we recently developed a novel automated NTBI quantification system capable of measuring large numbers of samples. In the present study, we investigated the in vivo behavior of NTBI in human and animal serum using this newly established automated system. Average NTBI in healthy volunteers was 0.44 ± 0.076 µM (median 0.45 µM, range 0.28-0.66 µM), with no significant difference between sexes. Additionally, serum NTBI rapidly increased after iron loading, followed by a sudden disappearance. NTBI levels also decreased in inflammation. The results indicate that NTBI is a unique marker of iron metabolism, unlike other markers of iron metabolism, such as serum ferritin. Our new automated NTBI quantification method may help to reveal the clinical significance of NTBI and contribute to our understanding of iron overload.

Quercetin attenuates chronic ethanol hepatotoxicity: implication of "free" iron uptake and release.

Emerging evidence has displayed that oxygen free radicals especially ones promoted by "free" iron play an important role in the development of alcoholic liver disease (ALD). Naturally-occurring quercetin has been reported to prevent ALD and iron overload-induced damage aside from the "free" iron. The purpose was to explore the potential mechanisms by which quercetin arrests alcohol-induced "free" iron disorder. Chronic alcohol (30% of total calories) or iron (0.2%)-fed adult male C57BL/J mice for 15 weeks resulted in significantly elevated levels of hepatic iron, labile iron pool-Fe and serum non-transferrin bound iron, accompanied with sustained oxidative damage. The hepatotoxicity was further exacerbated by ethanol and iron. Quercetin (100 mg/kg. body weight) alleviated the detrimental effects induced by ethanol and/or iron. The expressions of divalent metal transporter 1, zinc transporter member 14, mucolipin 1, transferrin receptor 1 (TfR1) and ferritin were up-regulated by ethanol and/or iron, which were partially normalized by quercetin. Quercetin prevented ethanol-induced hepatotoxicity, which may be partially attributed to the alleviated disorder of bound iron and "free" iron. The significant suppression of ethanol-stimulated molecules for "free" iron uptake and release may contribute to the hepatoprotective effect of quercetin, although TfR1-mediated physiological pathway of iron uptake also played a role.

Angiotensin II inhibits uptake of transferrin-bound iron but not non-transferrin-bound iron by cultured astrocytes.

The existence of all components of the renin-angiotensin system (RAS) and the iron metabolism system, and the recent findings on the functions of angiotensin II (ANGII) in peripheral iron metabolism imply that ANGII might play a role in iron homeostasis by regulating expression of iron transport proteins in the brain. Here, we investigated effects of ANGII on uptake and release of iron as well as expression of cell iron transport proteins in cultured astrocytes. We demonstrated that ANGII could significantly inhibit transferrin-bound iron (Tf-Fe) uptake and iron release as well as the expression of transferrin receptor 1 (TfR1) and the iron exporter ferroportin 1 (Fpn1) in cultured astrocytes. This indicated that the inhibitory role of ANGII on Tf-Fe uptake and iron release is mediated by its negative effect on the expression of TfR1 and Fpn1. We also provided evidence that ANGII had no effect on divalent metal transporter 1 (DMT1) expression as well as non-transferrin-bound iron (NTBI) uptake in the cells. Our findings showed that ANGII has a role to affect expression of iron transport proteins in astrocytes in vitro and also suggested that ANGII might have a physiological function in brain iron homeostasis.

Mechanisms of brain iron transport: insight into neurodegeneration and CNS disorders.

Trace metals such as iron, copper, zinc, manganese, and cobalt are essential cofactors for many cellular enzymes. Extensive research on iron, the most abundant transition metal in biology, has contributed to an increased understanding of the molecular machinery involved in maintaining its homeostasis in mammalian peripheral tissues. However, the cellular and intercellular iron transport mechanisms in the central nervous system (CNS) are still poorly understood. Accumulating evidence suggests that impaired iron metabolism is an initial cause of neurodegeneration, and several common genetic and sporadic neurodegenerative disorders have been proposed to be associated with dysregulated CNS iron homeostasis. This review aims to provide a summary of the molecular mechanisms of brain iron transport. Our discussion is focused on iron transport across endothelial cells of the blood-brain barrier and within the neuro- and glial-vascular units of the brain, with the aim of revealing novel therapeutic targets for neurodegenerative and CNS disorders.