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PubMed1995

Changed transferrin sialylation in Parkinson's disease.

Variation in the sialylation pattern of transferrin was studied in serum and cerebrospinal fluid (CSF) of 90 patients with Parkinson's disease (PD), dementing and non-dementing, de novo and treated, and was compared with the variation observed in a group of 21 age-matched healthy controls. In serum and CSF of PD patients the proportional contribution of the different sialo-transferrins was independent of sex or dementia. However, a significant shift was found towards the more sialylated fractions for serum transferrin in both de novo and treated PD patients. This shift was not observed for CSF transferrin. The contribution of the tau-transferrin fraction, reduced in de novo PD patients, returns on treatment to the level observed for healthy controls. These observations may be important, as the degree of sialylation of transferrin in serum and CSF plays a role in the homeostasis of iron, and suggest that alterations in transferrin sialylation may play a role in the pathophysiology of PD.

Aged↗
PubMed1991

Axonal transport and release of transferrin in nerves of regenerating amphibian limbs.

Transferrin, a plasma protein required for proliferation of normal and malignant cells, is abundant in peripheral nerves of birds and mammals and becomes more concentrated in this tissue during nerve regeneration. We are testing the hypothesis that this factor is involved in the growth-promoting effect of nerves during the early, avascular phase of amphibian limb regeneration. A sensitive enzyme-linked immunosorbent assay for axolotl transferrin was developed and used to determine whether this protein meets certain criteria expected of the trophic factor(s) from nerves. During limb regeneration adult sciatic nerves greatly increased their content of transferrin, which immunohistochemistry revealed was distributed in both axons and Schwann cells. Using the double ligature method with sciatic nerves in vivo, it was determined that transferrin is carried by fast anterograde axonal transport at all stages of limb regeneration. An approach based on multicompartment organ culture demonstrated that fast-transported transferrin was secreted in physiologically significant amounts at distal ends of regenerating axons. Finally, the concentration of transferrin in the distal region of larval axolotl limb stumps was found to decrease directly and rapidly in response to axotomy. Since transferrin is important for both axonal regeneration and cell cycling, the present data have significance for various aspects of nerve's trophic activity during limb regeneration.

Ambystoma↗
PubMed1982

Transferrin protein and iron uptake by cultured hepatocytes.

The binding and uptake of 59Fe-loaded 3H-labelled rat transferrin by cultured rat hepatocytes was investigated. At 4 degrees C, there is no evidence for a specific binding of transferrin which could be related to the association of neo-synthesized transferrin with plasma membrane receptors. At 37 degrees C, iron uptake is much more important than transferrin uptake; it proceeds linearly over the time of incubation, is largely proportional to the extracellular transferrin concentration, and is compatible with uptake by fluid phase endocytosis. The difference observed between iron and transferrin uptake implies the existence of a mechanism allowing the reutilization of transferrin after iron delivery.

Animals↗
PubMed1984

PAC studies of 111In binding to transferrin, tropolone and acetylacetone in aqueous solutions.

Time integral and time-differential PAC measurements have been made over a wide temperature range in aqueous solutions of [111In]tropolonate and [111In]acetylacetonate. The quadrupole frequency in the latter is approximately 30% higher than that in the former and the molecular volumes derived from rotational correlation times show the expected differences. Apo-transferrin was separately added to the two 111In-chelates and the transfer of activity from chelate to transferrin followed as a function of relative molar concentrations. Very much larger molar ratios of transferrin to tropolone than of transferrin to acetylacetone were required before substantial transfer of 111In from chelate to transferrin took place. This difference in affinity for transferrin could be one significant factor in explaining the enhanced ability of [111In]tropolonate to label blood cells in the presence of plasma. The determination of PAC parameters in [111In]transferrin over a range of temperatures showed that the values of quadrupole frequency obtained depended on the number of binding sites assumed. For only one 111In site per molecule, the quadrupole frequency increases by over 50% as the temperature is reduced below the freezing point of the solution. If two 111In sites are assumed there appears to be a change in the percentage occupancy of the two sites on either side of the transition.

Cycloheptanes↗
PubMed1989

Comparison of the regional distribution of transferrin receptors and aluminium in the forebrain of chronic renal dialysis patients.

Recent studies have emphasised the potential neurotoxicity of aluminium in dialysis encephalopathy and it has also been suggested that this element may have a role in the pathogenesis of Alzheimer's disease. Aluminium is known to be transported by the iron transport protein transferrin. In this study using receptor autoradiography we have demonstrated the presence of transferrin binding sites in the human forebrain and shown a pattern similar to that found in other species. Imaging secondary ion mass spectrometry has demonstrated the distribution of aluminium-containing cell-like profiles in the brains of chronic renal dialysis patients who have raised levels of brain aluminium (greater than 4 micrograms/g dry weight) and even in dialysis patients where the gross level of aluminium was within the normal range. The density of these profiles corresponded to the regions of high transferrin receptor density. In contrast, the distribution of iron in the brain showed an inverse correlation with transferrin receptor density with highest iron levels present in the globus pallidus, an area of low transferrin receptor density. These results suggest that the regional distribution of neuropathological changes seen in dialysis encephalopathy patients and also Alzheimer's disease may reflect the distribution of transferrin receptors. The discrepancy between iron distribution and transferrin receptor distribution suggests that further, as yet uncharacterized mechanisms, govern the distribution of brain iron.

Adult↗
PubMed1990

Tissue specific expression of mouse transferrin during development and aging.

Transferrin (TF) is a major plasma protein that binds ferric iron and transports it to all target tissues of the body. This study is the first step to identify the tissue specific expression of the transferrin gene in mice during development, into maturity and throughout the aging process. The transferrin gene expresses mainly in mouse liver, the cerebral hemispheres and cerebellum. In mouse, transferrin is expressed in peritoneal macrophages and in mouse macrophage cell line MO59. At 19 days of gestation, transferrin mRNA is detected in the fetal lung, heart, stomach and kidney. TF mRNA levels increase in liver throughout gestation with maximum expression occurring at 19 days. Transferrin mRNA was detected in placentas of pregnant mice, with levels progressively increasing throughout the term of pregnancy. The levels of liver TF mRNA in mouse vary in a cyclic manner during the development increasing with the aging processes. Because of the dynamic nature of tissue requirements for transferrin during homeostasis the TF gene serves as a promising system for analyzing tissue-specific regulation in vivo during development and aging. Results from this study designate periods in the life-span of the mouse where regulatory mechanisms interacting with the TF gene appear to dynamically alter its expression.

Aging↗
PubMed1984

Decreased serum transferrin concentration in children with the nephrotic syndrome: effect on lymphocyte proliferation and correlation with serum immunoglobulin levels.

Recent evidence suggests that transferrin has immunoregulatory functions. In the nephrotic syndrome, excessive urinary losses can produce hypotransferrinemia. Whether low serum transferrin concentration in children with the nephrotic syndrome is related to their decreased immunoglobulin concentrations and to the decreased in vitro response of lymphocytes to a mitogen was studied. Twenty patients, 2 to 15 years of age, were studied. Fifteen patients had the nephrotic syndrome and 5 had other renal disorders. Of 13 patients with nephrotic syndrome in relapse, serum transferrin and gamma-globulin concentrations were decreased in 10 and 11 patients, respectively. Transferrin levels correlated with the concentrations of total protein (r = 0.87, P less than 0.001), albumin (r = 0.91, P less than 0.001), and gamma-globulin (r = 0.78, P less than 0.001). Urinary electrophoretic analyses suggested that hypogammaglobulinemia was not explained simply by urinary losses. In order to determine whether decreased serum transferrin concentrations might limit immunoglobulin synthesis, the effect of hypotransferrinemic sera on lymphocyte proliferation in vitro was tested. At low concentrations of serum, tritiated thymidine uptake was directly proportional to the serum transferrin concentration (r = 0.86, P less than 0.001 at 0.02% serum concentration). Addition of transferrin completely restored the ability of patients' sera to support lymphocyte proliferation. These results suggest that hypotransferrinemia might influence in vivo lymphocyte function and immunity in the nephrotic syndrome.

Adolescent↗
PubMed1984

Analysis of transferrin recycling in mitotic and interphase HeLa cells by quantitative fluorescence microscopy.

Recent findings suggest that membrane vesicle transport during mitosis may be generally inhibited. To test this, we examined the kinetics of uptake and exocytosis of RITC-transferrin in mitotic and interphase HeLa cells. We used quantitative image-intensification fluorescence microscopy to analyze the content of ligands in single cells. This technique was validated by comparison of 3H or RITC-transferrin release from interphase cells determined by microscopy or radiometry. Both methods gave a t1/2 of release of 5-6 min. The uptake of RITC-transferrin was depressed in mitotics. More importantly, we monitored the exocytosis of label during mitosis. Labeled mitotics were obtained by the progression of interphase cells into mitosis during a 50 min incubation with RITC-transferrin. After 30 min chase with unlabeled transferrin, the intensities of interphase cells approached background, whereas those of mitotic cells remained nearly constant. Thus both exocytosis and endocytosis of transferrin were exocytosis and endocytosis of transferrin were blocked during mitosis.

Fluorescent Dyes↗
PubMed1984

Binding of vanadate to human serum transferrin.

Human serum transferrin specifically and reversibly binds 2 equiv of vanadate at the two metal-binding sites of the protein. The vanadium(V)-transferrin complex can be formed either by the addition of vanadate to apotransferrin or by the air oxidation of the vanadyl(IV)-transferrin complex. The formation of the vanadium complex can be blocked by loading the apotransferrin with iron(III), and bound vanadium can be displaced from the protein by the subsequent addition of either gallium(III) or iron(III). The binding constant for the second equiv of vanadate is 10(6.5) in 0.1 M hepes, pH 7.4 at 25 degrees C. The binding constant for the first equiv of vanadate is probably very similar, although no quantitative value could be determined. Although transferrin reacts with the vanadate anion, studies on the transferrin model compound ethylenebis(o-hydroxyphenylglycine) indicate that at pH 9.5, the vanadium is binding at the metal-binding site as a dioxovanadium(V) cation coordinated to two phenolic residues at each binding site. This bound cation appears to be protonated over the pH range 9.5-6.5, as shown by changes in the difference uv spectrum of the transferrin complex, to produce an oxohydroxo species. Further decreases in the pH lead to dissociation of the vanadium-transferrin complex.

Binding Sites↗
PubMed1987

A simple one-column procedure for the separation of swine and human serum transferrins.

A rapid method for the separation of transferrin from swine or human serum is described. Serum (human or swine) is brought to 50% of saturation with ammonium sulfate for removal of immunoglobulins, the resulting precipitate discarded and the supernatant brought to 70% of saturation. The resulting precipitate was dissolved in and dialyzed against 1.54 mM sodium azide (I = 0.00154). Chromatography of the low ionic strength ammonium sulfate fractions (= 20 ml of swine or human serum, 70% of saturation) on columns of Bio-Gel A-1.5 m-Reactive Blue 2, equilibrated with 1.54 mM sodium azide, resulted in two peaks, a breakthrough peak and pure transferrin which was eluted with a linear gradient with 0.5 M potassium phosphate buffer, pH 7.1, as limit buffer. Yields varied between 53 and 55% from whole serum and 70-76% from the ammonium sulfate fractions. Transferrins from both species were found to be homogeneous when subjected to immunoelectrophoresis (anti whole serum antibody) and anionic and sodium dodecyl sulfate polyacrylamide disc gel electrophoresis. Hemopexin, a frequently found contaminant in transferrin preparations, is tightly bound by the gel-dye complex under the experimental conditions. Swine serum transferrin possesses many physicochemical properties practically identical to the human protein. Although small differences in physicochemical properties were apparent the extinction coefficients, molecular weights, electrophoretic mobilities, absorbance maxima of the diferric proteins (470 nm), isoelectric points and the absorbance ratios (465 nm/410 nm) of the diferric proteins were practically identical. Both swine and human transferrin produced a reaction of identity (complete coalescence) when reacted with antibody to either transferrin.

Animals↗
PubMed1984

Intracellular segregation of asialo-transferrin and asialo-fetuin following uptake by the same receptor system in suspended hepatocytes.

Asialo-transferrin and asialo-fetuin are both taken up into suspended hepatocytes by the asialo-glycoprotein receptor and with similar kinetics (Tolleshaug, H., Chindemi, P. and Regoeczi, E. (1981) J. Biol. Chem. 265, 6526-6528). However, the intracellular fate of the two ligands differ. Asialo-fetuin is carried to the lysosomes and degraded. Internalized asialo-transferrin is recycled with the receptors back to the cell surface, from which it may be released by calcium chelators. In the current studies, we fractionated cell homogenates in sucrose density gradients in order to trace the pathways taken by asialo-transferrin and asialo-fetuin within the cells. More than one-half of the intracellular asialo-transferrin sedimented within a novel kind of 'light' endosomes which were recovered at 1.11 g/ml in sucrose gradients. When cells were fractionated 6 min after the addition of trace concentrations of 125I-asialo-fetuin and 131I-asialo-transferrin, their intracellular distributions were found to be roughly similar. After 24 min their distributions were clearly disparate, relatively more asialo-fetuin being recovered in a peak of heavy endosomes at 1.15 g/ml. The ligand molecules in this part of the gradient (e.g., asialo-fetuin) were delivered to the lysosomes to be degraded, while the material in the lighter peak was degraded much more slowly. The data indicate that asialo-fetuin and asialo-transferrin enter a light endosome fraction immediately after receptor-mediated endocytosis. Subsequently, they are separated; the asialo-transferrin remains receptor-bound and is returned to the cell surface, while the asialo-fetuin is transferred to endosomes of density 1.15 g/ml and is eventually degraded in the lysosomes.

Animals↗
PubMed1991

Effects of calcium on hepatocyte iron uptake from transferrin, iron-pyrophosphate and iron-ascorbate.

Calcium stimulates hepatocyte iron uptake from transferrin, ferric-iron-pyrophosphate and ferrous-iron-ascorbate. Maximal stimulation of iron uptake is observed at 1-1.5 mM of extra-cellular calcium and the effect is reversible and immediate. Neither the receptor affinity for transferrin, nor the total amounts of transferrin associated with the cells or the rate of transferrin endocytosis are significantly affected by calcium. In the presence of calcium the rate of iron uptake of non-transferrin bound iron increases abruptly at approximate 17 degrees C and 27 degrees C and as assessed by Arrhenius plots, the activation energy is reduced in a calcium dependent manner at approx. 27 degrees C. At a similar temperature, i.e., between 25 degrees C and 28 degrees C, calcium increases the rates of cellular iron uptake from transferrin in a way that is not reflected in the rate of transferrin endocytosis. By the results of this study it is concluded that calcium increases iron transport across the plasma membrane by a mechanism dependent on membrane fluidity.

Animals↗
PubMed1978

Differences between human and rabbit transferrins.

Rabbit reticulocyte incorporation of iron from rabbit transferrin was independent of transferrin iron saturation but uptake from human transferrin was saturation dependent. Unlike human transferrin, rabbit transferrin does not surrender its iron from any unique preferred iron-binding site and can be described as functionally homogeneic. The two proteins also differ in their acid-base iron-binding properties. One human transferrin iron binding site retains an ability to bind iron at somewhat acid pH but this property is not shared by rabbit transferrin.

Animals↗
PubMed1991

Diferric transferrin reduction by K562 cells. A critical study.

This paper critically examines the redox activity of K562 cells (chronic myelogenous leukemia cells) and normal peripheral blood lymphocytes (PBL). Ferricyanide reduction, diferric transferrin reduction, and ferric ion reduction were measured spectrophotometrically by following the time-dependent changes of absorbance difference characteristic for ferricyanide disappearance and for the formation of ferrous ion:chelator complexes. Bathophenanthroline disulfonate (BPS) and ferrozine (FZ) were used to detect the appearance of ferrous ions in the reaction mixtures when diferric transferrin or ferric reduction was studied. Special attention was devoted to the analysis of time-dependent absorbance changes in the presence and absence of cells under different assay conditions. It was observed and concluded that: (i) FZ was far less sensitive and more sluggish than BPS for detecting ferrous ions at concentrations commonly used for BPS; (ii) FZ, at concentrations of at least 10-times the commonly used BPS concentrations, seemed to verify the results obtained with BPS; (iii) ferricyanide reduction, diferric transferrin reduction and ferric ion reduction by both K562 cells and peripheral blood lymphocytes did not differ significantly; and (iv) earlier values published for the redox activities of different cells might be overestimated, partly because of the observation published in 1988 that diferric transferrin might have loosely bound extra iron which is easily reduced. It is suggested that the specific diferric transferrin reduction by cells might be considered as a consequence of (i) changing the steady-state equilibrium in the diferric transferrin-containing solution by addition of ferrous ion chelators which effectively raised the redox potential of the iron bound in holotransferrin, and (ii) changing the steady-state equilibrium by addition of cells which would introduce, via their large and mostly negatively charged plasma membrane surface, a new phase which would favor release and reduction of the iron in diferric transferrin by a ferric ion oxidoreductase. The reduction of ferricyanide is also much slower than activities reported for other cells which may indicate reduced plasma membrane redox activity in these cells.

Ferricyanides↗
PubMed1987

Transferrin gene expression in choroid plexus of the adult rat brain.

Transferrin immunoreactivity and transferrin messenger RNA (mRNA) were recently found to be present in oligodendrocytes of the adult rat brain by using immunohistochemistry and in situ hybridization procedure. The present study demonstrates, in the same way, that epithelial cells of the choroid plexus also contain transferrin together with transferrin mRNA. Choroid plexus of the lateral and the third ventricle are rich in transferrin mRNA, while choroid plexus of the fourth ventricle contain few if any transferrin mRNA. These results demonstrate that epithelial cells of the choroid plexus as well as oligodendrocytes express the transferrin gene in the adult rat brain.

Animals↗
PubMed1995

Effects of insulin-like growth factor-I, estrogen, glucocorticoid, and transferrin on the mRNA contents of ovalbumin and conalbumin in primary cultures of quail (Coturnix coturnix japonica) oviduct cells.

The effects of estrogen, dexamethasone, insulin-like growth factor-I (IGF-I), and transferrin on the messenger RNA (mRNA) contents of ovalbumin and conalbumin in primary cultures of quail oviduct cells were investigated. In the absence of one of the above hormones or factors, a decrease in ovalbumin mRNA was prominent. In particular, removal of IGF-I and transferrin caused a significant effect. Studies using a combination of estrogen, dexamethasone, IGF-I and transferrin indicated that IGF-I cooperates with estrogen or dexamethasone and transferrin works with dexamethasone. Specifically, IGF-I enhanced ovalbumin synthesis or increased cellular ovalbumin mRNA content depending on its concentration in the medium in the presence of estrogen. However, the effects of estrogen, dexamethasone, IGF-I, and transferrin were not similarly observed with conalbumin mRNA. These results show that ovalbumin synthesis is controlled by estrogen or glucocorticoid with IGF-I or transferrin and that cellular ovalbumin mRNA content is also regulated by these hormones or transferrin. In contrast, conalbumin synthesis and cellular content of conalbumin mRNA are not affected by these hormones under the conditions of the present study.

Animals↗
PubMed2006

Association of serum transferrin receptor concentration with markers of inflammation in Zimbabwean children.

BACKGROUND: Clinical studies have shown that degree of erythropoiesis, the hypoxic response, and iron status each independently influences transferrin receptor concentration, but there is conflicting information regarding the effect of inflammation on transferrin receptor expression. SUBJECTS AND METHODS: Levels of hemoglobin, reticulocytes, serum ferritin, transferrin receptors and inflammatory markers (C-reactive protein, interleukin-6 and neutrophils) were determined in 208 Zimbabwean children 10 ng/mL that adjusted for erythropoiesis with log(10) reticulocyte count, the hypoxic response with hemoglobin concentration and iron status with log(10) ferritin concentration, positive correlations were found between log(10) transferrin receptor concentration and log(10) C-reactive protein concentration (P=0.012), log(10) interleukin-6 concentration (P=0.011) and log(10) neutrophil count (P=0.013). These models predict that, with a baseline transferrin receptor concentration in the upper normal range of 8.0 mg/L and holding hemoglobin concentration and reticulocyte count constant, an increase from 1 to 10 mg/L in C-reactive protein is associated with a rise of 1.6 mg/L in transferrin receptor (95% C.I. 0.3-3.0 mg/L), an increase from 0.5-to-5.0 pg/mL in interleukin-6 with a rise of 1.9 mg/L (0.4-3.7 mg/L), and an increase from 2000 to 20,000/microL in neutrophil count with a rise of 3.6 mg/L (0.7-7.5 mg/L). CONCLUSION: Our results suggest that inflammation leads to an increase in circulating transferrin receptor concentration that is independent of the degree of erythropoiesis, the hypoxic response and iron status.

Biomarkers↗
PubMed2006

Lipoplexes with biotinylated transferrin accessories: novel, targeted, serum-tolerant gene carriers.

Novel transfecting assemblies comprising biotinylated cationic liposomes, DNA and tribiotinylated transferrin-streptavidin (streptavidin(bio3-transferrin)) accessories have been prepared, characterized and evaluated for toxicity and DNA delivery capability in human cervical carcinoma cells (HeLa). Two new lipophilic cholesteryl-based biotin derivatives, biotinylcholesterylformylhydrazide (MSB1) and aminohexanoylbiotinylcholesterylformylhydrazide (MSB2) provided docking points for streptavidin(bio3-transferrin) on cationic liposomes which were formulated with N,N-dimethylaminopropylaminylsuccinylcholesterylformylhydrazide (MS09) and dioleoylphosphatidylethanolamine (DOPE) in a 2:48:50 molar ratio. Ethidium dye displacement assays and gel retardation studies suggest that in ternary complexes, the DNA is electrostatically bound to the cationic liposomes while transferrins remain liposome-bound through streptavidin-biotin interactions. Assemblies fully protected plasmid DNA from serum nuclease digestion over a range of liposome:pGL3 DNA ratios (3-8:1, w/w) and exhibited low growth inhibition of HeLa cells (circa 5%) at the optimal transfection composition for streptavidin(bio3-transferrin):liposome:pGL3 DNA of 10:6:1 (w/w/w). Transfection levels, which were twice those of untargeted lipoplexes containing MSB1 or MSB2, were not significantly diminished in the presence of 10% foetal bovine serum. Excess transferrin (200 microg per well) reduced transfection levels to those of untargeted complexes, supporting the notion that at least 50% of ternary complexes gained entry into the cervical carcinoma cells by receptor mediation. Conversely, transfection levels with untargeted lipoplexes were only slightly reduced in the presence of transferrin at the same concentration.

HeLa Cells↗