Receptor assay with radiolabeled transferrin

Analysis of anemia and iron supplementation among glioblastoma patients reveals sex-biased association between anemia and survival

The association between anemia and outcomes in glioblastoma patients is unclear. We analyzed data from 1346 histologically confirmed adult glioblastoma patients in the TriNetX Research Network. Median hemoglobin and hematocrit levels were quantified for 6 months following diagnosis and used to classify patients as anemic or non-anemic. Associations of anemia and iron supplementation of anemic patients with median overall survival (median-OS) were then studied. Among 1346 glioblastoma patients, 35.9% of male and 40.5% of female patients were classified as anemic using hemoglobin-based WHO guidelines. Among males, anemia was associated with reduced median-OS compared to matched non-anemic males using hemoglobin (HR 1.24; 95% CI 1.00-1.53) or hematocrit-based cutoffs (HR 1.28; 95% CI 1.03-1.59). Among females, anemia was not associated with median-OS using hemoglobin (HR 1.00; 95% CI 0.78-1.27) or hematocrit-based cutoffs (HR: 1.10; 95% CI 0.85-1.41). Iron supplementation of anemic females trended toward increased median-OS (HR 0.61; 95% CI 0.32-1.19) although failing to reach statistical significance whereas no significant association was found in anemic males (HR 0.85; 95% CI 0.41-1.75). Functional transferrin-binding assays confirmed sexually dimorphic binding in resected patient samples indicating underlying differences in iron biology. Anemia among glioblastoma patients exhibits a sex-specific association with survival.

Rapid diagnostics for point-of-care quantification of soluble transferrin receptor

Background

Iron deficiency (ID) and anaemia are major health concerns, particularly in young children. Screening for ID based on haemoglobin (Hb) concentration alone has been shown to lack sensitivity and specificity. The American Academy of Pediatrics (AAP) recommends soluble transferrin receptor (sTfR) as a promising approach to screen for iron deficiency. However, in most settings, assessment of iron status requires access to centralized laboratories. There is an urgent need for rapid, sensitive, and affordable diagnostics for sTfR at the point-of-care.

Methods

An immunochromatographic assay-based point-of-care screening device was developed for rapid quantification of sTfR from a drop of serum within a few minutes. Performance optimization of the assay was done in sTfR-spiked buffer and commercially available sTfR calibrator, followed by a small-scale proof-of-concept validation with archived serum samples.

Findings

On preliminary testing with archived serum samples and comparison with Ramco ELISA, a correlation of 0.93 (P < 0.0001) was observed, demonstrating its potential for point-of-care assessment of iron status.

Interpretation

The analytical performance of the point-of-care sTfR screening device indicates the potential for application in home-use test kits and field settings, especially in low- and middle-income settings. An added advantage of sTfR quantification in combination with our previously reported serum ferritin diagnostics is in integration of Cook's equation as a quantitative and minimally-invasive indicator of total body iron stores.

Fund

Thrasher Research Fund (Early Career Award #13379), NIH R03 EB 023190, NSF grant #1343058, and Nutrition International (project #10-8007-CORNE-01).

Evaluation of new immunoenzymometric assay for measuring soluble transferrin receptor to detect iron deficiency in anemic patients

During the last few years the measurement of serum-soluble transferrin receptor (sTfR) has been introduced as a tool to detect iron deficiency and as an analyte to differentiate between anemia caused by iron deficiency (IDA) and that caused by chronic disease (ACD). Commercially available methods have emerged to make diagnostics by sTfR more readily accessible. We documented the analytical performance of a newly introduced IDeATM sTfR immunoenzymometric assay (IEMA) by Orion Diagnostica. We also evaluated its clinical performance in 98 consecutive anemic patients, with information derived from bone marrow aspirate samples as the reference for iron status. The clinical usefulness of two other commercially available sTfR assays was assessed for comparison. The analytical performance and clinical applicability of the IDeA were sufficient to support reliable clinical work. We conclude that IDA and iron deficiency in the presence of inflammatory states can be differentiated efficiently from ACD with this new commercial test to measure sTfR.

Alteration in the organ distribution of iron by truncated transferrin: implications for iron chelation therapy

The ability of the partial molecule of transferrin, truncated transferrin (t-Tf), to act as an excretable biologic iron chelator was examined. We confirmed the observations of Zak and Aisen (Zak O, Aisen P. Biochem Biophys Acta 1985;1952:24-8) that thermolysin treatment of human transferrin produces half molecules that retain iron-binding capacity. These molecules are poorly recognized by surface receptors on either human or murine cells. Although the plasma half-life of human transferrin in mice is moderately long (40 hours), injection of t-Tf into mice results in its rapid clearance (half-life = 10 minutes). Injection of iron 59-labeled transferrin results in the deposition of iron in the major hematopoetic organs of mice such as the spleen, bone marrow, and liver. Injection of 59Fe-labeled t-Tf results in the quantitative recovery of iron in the kidneys: 59Fe is retained in the kidney for substantial periods of time with little evidence of its excretion into urine. Injection of iodine 125-labeled t-Tf also results in the deposition of radioactivity in the kidneys, but 125I is rapidly excreted into the urine, where it is detected as free iodine. These results indicate that although t-Tf is directed to the kidney and filtered by the glomerulus, the molecule is reabsorbed and degraded, and iron is retained. These results have implications in the design of iron chelators.

Apotransferrin stimulation of thyroid hormone dependent rat pituitary tumor cell growth in serum-free chemically defined medium: role of FE(III) chelation

Triiodothyronine (T3) dependent growth of GH1 rat pituitary tumor cells in serum-free defined culture requires apotransferrin (apoTf) (Sirbasku et al.: Mol. Cell. Endocrinol., 77:C47-C55, 1991). Diferric transferrin (2Fe.Tf) also is necessary as an iron source (Eby et al.: Anal. Biochem., 203:317-325, 1992). Further, T3 dependence is prevented by soluble Fe(III) addition to the medium (Sato et al.: In Vitro Cell. Dev. Biol., 27A:599-602, 1991). While our data suggested that apoTf caused growth by chelation of Fe(III), direct evidence was required. We used urea polyacrylamide gel electrophoresis along with autoradiography and Western immunoblotting to measure the Fe(III) content of growing GH1 cell cultures and identify the apoTf, mono-metal transferrins and 2Fe.Tf present. We found that apoTf per se did not cause growth but instead chelated inhibitory levels of Fe(III). In fact, apoTf need not be present at all provided that Fe(III) is reduced to < or = 0.6 microM. In addition, other protein and non-protein Fe(III) chelators were shown to be as effective as apoTf. Here, we report that pituitary cells are completely inhibited by > or = 1.2 microM Fe(III), which are concentrations which might be expected in many culture media and usually are not thought to influence growth. The high sensitivity of pituitary cells to Fe(III) suggests further study to determine what cellular functions are affected and how they interfere with thyroid hormone dependence.

Apotransferrins from several species promote thyroid hormone-dependent rat pituitary tumor cell growth in iron-restricted serum-free defined culture

Previously, we have studied thyroid hormone-dependent growth of GH1 rat pituitary tumor cells in iron-restricted serum-free defined medium (Sirbasku, D.A., et al. (1991) Biochemistry 30, 295-304, 7466-7477). Proliferation was promoted by triiodothyronine (T3) and any of seven forms of horse serum-derived apotransferrin (apoTf). In this report, we have asked if apoTfs from other species also acted as thyromedins and if other metal ion chelators served this role. To address these issues, three thyromedins were isolated from human serum and identified as apoTf. Fe3+ depletion, and assay in low-Fe medium, gave ED50s of 1.4-1.7 nM. Fe3+ saturation abolished their activities in high-Fe medium. To ask if apoTf was the major thyromedin in human serum, hormone-depleted preparations were iron saturated and shown to no longer support T3-dependent GH1 cell growth. Next, commercially prepared human, rat, horse, dog, rabbit, guinea pig and mouse apoTfs were shown to be as active under iron-restricted conditions as those isolated from human serum. Bovine apoTf and colostrum lactoferrin were greater than 100-fold less active; human milk apo-lactoferrin and apo-ovotransferrins were inactive. Transferrins which displayed thyromedin activity blocked the binding of 125I-rat 2Fe.Tf to GH1 cell receptors while those without thyromedin activity were ineffective. Finally, the metal ion chelators EDTA, citrate and deferoxamine did not show thyromedin activity indicating that apoTfs uniquely were able to promote T3-dependent cell growth in defined culture.

Thyroid hormone dependent pituitary tumor cell growth in serum-free chemically defined culture. A new regulatory role for apotransferrin

Thyroid hormone dependent GH1 rat pituitary tumor cell growth in serum-free chemically defined medium required a serum-derived mediator (i.e., thyromedin) which was identified as transferrin [Sirbasku, D.A., Stewart, B.H., Pakala, R., Eby, J.E., Sato, H., & Roscoe, J.M. (1990) Biochemistry 30, 295-304]. The transferrin isolated was consistent with the equine R or D variants and was biologically active only as apotransferrin (apoTf). To determine if other variants of horse transferrin also were thyromedins, a purification was developed which yielded seven separate forms. Initially, only four of these had activity when assayed in standard "iron salts containing" medium (ED50 values of 290-1160 nM). To further assess activity, the iron contents of all seven were altered either by saturation with ferric ammonium citrate or by citrate/acid depletion of the metal ion. Thereafter, potencies were compared in "iron salts containing" and "iron salts reduced" media. All seven variants proved to be active as apoTf. Bioassays in which apoTf was maximized showed ED50 values of 2.1-3.8 nM. Conversely, assays in which thyromedins were converted to Tf.2Fe showed no activity. Previously, the only known physiological function of apoTf was that of a carrier/detoxifier of iron; this study indicates a new role in hormone-dependent pituitary cell growth.

Thyroid hormone regulation of rat pituitary tumor cell growth: a new role for apotransferrin as an autocrine thyromedin

In the 40 years of transferrin research, no previous role for apotransferrin has been recognized other than to serve as a plasma carrier for dietary and storage iron. Our studies have revealed a new 'autocrine' growth role for this molecule as well as a possible new cell-cell bridge/CAM function. Certainly, these observations have opened many new areas of investigation both with regard to thyroid hormone action and the function of apotransferrin. In addition, there is now accessible the broader question of tissues other than pituitary which might utilize apotransferrin to regulate responsiveness to thyroid hormones.