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PubMed1993

Tracing iron and transferrin in the macrophage by visual means.

The purpose of the study was to investigate the movement of iron and transferrin in the macrophage using light and electron microscopy. First, depicted here are the phagocytosis of antibody sensitized murine red cells by the murine bone marrow derived macrophage and the formation of red cell phagosomes. Second, we show the fusion of the lysosomes with the red cell phagosome to form a lysophagosome and the lysis of the red cell using acid phosphatase as a lysosome marker. Third by autoradiography, the presence of 55Fe silver grains in the phagocytosed red cells and its delivery to the organelles of the macrophage are demonstrated. Fourth a transferrin species is shown in red cells of all ages, in the phagocytosed as well as the non-phagocytosed, and in the phagocytosed as well as the non-phagocytosed, and in the macrophage itself. Transferrin was detected using immunogold and fluorescence labelling. These studies suggest that iron, using vesicles as means of transport, moves from the effete red cells inside the macrophage to the outside possibly bound to transferrin.

Animals↗
PubMed1993

Ferritin, transferrin, and iron in selected regions of the adult and aged rat brain.

Iron is necessary for normal neural function but it must be stringently regulated to avoid iron-induced oxidative injury. The regulation of systemic iron is through the proteins transferrin (iron mobilization) and ferritin (iron sequestration). This study examines the cellular and regional distribution of iron and the iron-related proteins ferritin and transferrin in selected regions of the adult and aged rat brain. This information is a necessary prerequisite to understanding the mechanism by which iron homeostasis is maintained in the brain. The predominant cell type containing ferritin, transferrin, and iron throughout the brain at all ages is the oligodendrocyte. Neurons in most brain regions contain granular iron deposits which become more apparent with age. Ferritin and iron are also present in microglial cells in all brain regions, but are particularly abundant in the hippocampus. These latter cells visibly increase in number in all brain regions as the animal approaches senescence. Another area in which immunostaining is notable is surrounding the III ventricle, where transferrin is found in the choroid plexus and ependyma and ferritin and iron are present in tanycytes. The results of this study indicate an important role for neuroglia in the regulation of iron in the brain and also implies that a transport system may exist for the transfer of iron between the brain and cerebrospinal fluid. In the normal rodent brain, the principal cell of iron regulation is the oligodendrocyte; however, the role of microglial cells in the sequestration and detoxification of iron may be significant, particularly as the animal ages. With age there is an increase in stainable iron in neurons without a concomitant increase in neuronal ferritin immunostaining, suggesting a ferritin independent accumulation of neuronal iron with age.

Aging↗
PubMed2004

Expression analyses of zebrafish transferrin, ifabp, and elastaseB mRNAs as differentiation markers for the three major endodermal organs: liver, intestine, and exocrine pancreas.

In the present work, three zebrafish cDNA clones encoding transferrin, intestinal fatty acid binding protein (IFABP), and elastaseB were cloned and their expression patterns in early zebrafish development were characterized as differentiation markers for the three major endoderm organs: liver, intestine, and exocrine pancreas. transferrin and ifabp mRNAs exhibit a biphasic expression pattern during early development. transferrin mRNAs were first expressed at approximately 7 hours postfertilization (hpf) in the yolk syncytial layer (YSL) and later in the liver rudiment (from approximately 48 hpf) and in the esophagus transiently (72-96 hpf). Ifabp mRNAs were initially expressed in the YSL at the ventral side during late epiboly (8-9 hpf), spread throughout the YSL of later stage embryos, and appeared in the intestine rudiment at approximately 36 hpf. In contrast to the transferrin and ifabp mRNAs, elastaseB mRNAs were not expressed in the yolk sac or YSL, and these transcripts were detected exclusively in the exocrine pancreas after approximately 56 hpf.

Amino Acid Sequence↗
PubMed1988

Different patterns of human serum transferrin on isoelectric focusing using synthetic carrier ampholytes or immobilized pH gradients.

Isoelectric focusing (IEF) of human serum transferrin allows splitting of the protein pattern into three forms corresponding to the diferric, monoferric and apoform. A detailed analysis of this pattern, performed on transferrin at different degrees of iron saturation, demonstrated that free Ampholine carrier ampholytes (CA) alter the expected results, always giving a complex pattern with multiple bands. In particular, the monoferric form appears to be the predominant one, regardless of the starting saturation of transferrin. In contrast to IEF-CA, the new technique of IEF in immobilized pH gradients (IPG), shows a much simpler pattern with the same samples. Moreover, the different transferrin forms are focused at the same pI values as in IEF-CA but the pattern appears to correspond to the expected distribution. IPG analysis gives a pattern similar to IEF-CA when free Ampholine CA are added either to the samples and/or as electrode solutions. A chelating action of Ampholine CA on Fe+3 might be responsible for these effects, while Immobilines, due to their different chemical nature or to the different focusing procedure, are not able to interact with iron.

Ampholyte Mixtures↗
PubMedDate not supplied

Separation of different forms of transferrin by isoelectric focusing to detect effects on the liver caused by xenobiotics.

Several genetic variants and also isoforms of transferrin differing in carbohydrate structure can be separated by polyacrylamide or agarose gel isoelectric focusing. Numerous blood plasma or serum samples can be analyzed in parallel in each gel. Studies of the heterogeneity of transferrin have already revealed many results of importance to different fields of human medicine. Gene typing can give important and useful information for paternity determination and in forensic medicine. The gene type C 2 seems to have increased frequency in certain malfunctions. Futhermore, functional abnormalities of liver cells can be revealed by determination of the concentrations of transferrin isoforms differing mainly in their carbohydrate parts. The isoforms can be quantified with zone immunoelectrophoresis assay. Thus valuable information can be obtained about important modulated regulations of cell and membrane functions, even when these are disturbed by disease and xenobiotics. The information may be useful e.g. in the detection of individuals suffering from toxic effects, to identify toxic agents and exposure conditions. Studies of house painters revealed that exposure to different types of paints had an effect on transferrin. Determination of the concentration of the isotransferrin with pI 5.7 in blood samples from alcoholics can be used as a marker for the detection of liver dysfunction and for the monitoring of therapy treatments. In addition, by analyzing the isotransferrins a rare genetic abnormality can be detected.

Alcoholism↗
PubMed1997

Analysis of carbohydrate deficient transferrin by capillary zone electrophoresis.

We report a capillary zone electrophoresis method to separate the various sialylated isoforms of transferrin. The separation is carried out under nondenaturing conditions and at basic pH. Under these conditions, transferrin exhibits two major and three minor peaks. Plasma samples from a population consuming varying amounts of alcohol at different intervals were studied. A cut-off value of 3% carbohydrate deficient transferrin (CDT: disialo, monosialo, and asialo transferrin), results in a clinical sensitivity of 88% in a population consuming at least 70 g/day alcohol for a minimum of two weeks. The sensitivity dropped significantly in a population consuming less than 70 g/day. This confirms previous reports of CDT as a specific marker for significant and chronic use of alcohol. Capillary electrophoresis offers an alternative method with respect to analysis time and throughput in the clinical laboratory.

Animals↗
PubMed1997

Transferrin receptor recycling in rat hepatocytes is regulated by protein phosphatase 2A, possibly through effects on microtubule-dependent transport.

To understand the regulation of receptor-mediated endocytosis in hepatocytes, we have used two specific inhibitors of serine-threonine protein phosphatases (PP), microcystin (MCYST) and okadaic acid (OKA) as probes to alter protein phosphorylation in hepatocytes. We have then examined the impact of these changes on the specific binding and uptake of transferrin (Tf) in hepatocytes. The measurement of PP activity in hepatocyte lysates showed that OKA and MCYST shared a common inhibition of protein phosphatase 2A (PP2A). Our results showed that both OKA (250 nmol/L) and MCYST (500 nmol/L) significantly reduced Tf uptake at steady state (P < or = .05). The measurement of Tf internalization after 15 minutes in protein phosphatase inhibitor-pretreated cells revealed that the initial uptake was also significantly reduced. Binding studies showed that pretreatment with either of the phosphatase inhibitors did not result in significant changes in the K(d) for Tf binding to transferrin receptor (TfR). Additionally, no significant changes in the number of TfR in the plasma membrane were observed in phosphatase inhibitor-pretreated cells. The treatment of hepatocytes with nocodazole (NOC), which results in microtubule disassembly and inhibition of microtubule-based vesicle transport, caused comparable reductions in initial and steady state levels of transferrin accumulation. The changes in transferrin accumulation by both phosphatase inhibitors and nocodazole were accompanied by redistribution of the microtubule-anchored Golgi apparatus and lysosomal network from the perinuclear region to the cell periphery. Our data show that the regulation of Tf uptake by receptor-mediated endocytosis is mediated by PP2A and additionally may occur through regulation of microtubule-based vesicle transport.

Animals↗
PubMed2002

Targeting of the photocytotoxic compound AlPcS4 to Hela cells by transferrin conjugated PEG-liposomes.

Photodynamic therapy has attracted increasing interest over the last few years, whereby the activation of photosensitizers by light causes the production of reactive oxygen species (ROS), such as singlet oxygen, which are cytotoxic. The goal of our study was to enhance the photodynamic activity of the photosensitizer aluminum phthalocyanine tetrasulfonate (AlPcS4) through its specific delivery to tumor cells. Since many tumor cells, among which are HeLa cells, overexpress the transferrin receptor, we synthesized transferrin conjugated PEG-liposomes that contained AlPcS4 that could be internalized by receptor mediated endocytosis. The antiproliferative activity of the targeted liposomes was evaluated and compared to the native AlPcS4 and the non-targeted liposome. These findings were supplemented with data on intracellular concentration of the photo-active compounds. The accumulation together with ROS production after irradiation was visualized by using confocal microscopy to confirm the data found in the antiproliferative and accumulation assay. Tf-Lip-AlPcS4 was 10 times more photocytotoxic (IC(50), 0.63 microM) than free AlPcS4 at a light dose of 45 kJ/m whereas Lip-AlPcS4 displayed no photocytotoxicity at all. The high photocytotoxicity of Tf-Lip-AlPcS4 was shown to be the result of a high intracellular concentration (136.5 microM) in HeLa cells, which could be lowered dramatically by incubating the conjugate with a competing transferrin concentration. The images of intracellular accumulation and ROS production matched the accumulation and photocytotoxicity profile of the different photo-active compounds. The photodynamic activity of the Tf-Lip-AlPcS4 conjugate on HeLa cells is much more potent than free AlPcS4 as a result of selective transferrin receptor mediated uptake.

Antineoplastic Agents↗
PubMedDate not supplied

Measurement of seminal LDH-X and transferrin in normal and infertile men.

LDH-X, an isoenzyme of lactate dehydrogenase specific for germinal epithelium activity, has been measured in the seminal plasma of infertile subjects whose infertility had different origins. In the same samples, seminal transferrin, an index of Sertoli cell function, was also measured. In this investigation, seminal LDH-X was not detectable in the vasectomized subjects, in patients with azoospermia due to seminiferous tubular damage, nor in patients who showed a marked decrease in sperm concentration (less than 1 X 10(6)/ml). In oligozoospermic patients (sperm concentration less than 20 X 10(6)/ml) seminal LDH-X levels were reduced to about one-third of those found in normal controls. Seminal LDH-X levels correlated (r = 0.7237) with total sperm count better than seminal transferrin levels (r = 0.5511), while no correlation was found between these two biochemical parameters and sperm motility, viability and morphology. To study their spontaneous variations with time, LDH-X and transferrin were also measured in semen specimens collected monthly from five healthy men, over 1 year. In these samples (N = 60), sperm count variability (43.1%, calculated in terms of the coefficient of variation), was similar to that of LDH-X (40.4%) and higher than for transferrin (23.0%).

Adult↗
PubMed2006

Serum level of sialic acid (SA) and carbohydrate-deficient transferrin (CDT) in type 2 diabetes mellitus with microvascular complications.

Sialic acid (SA) is responsible for the composition of different isoforms of transferrin and is reported to be a marker of microvascular complications in type 2 diabetes mellitus. Therefore, we explored the serum concentration of SA, and the less sialylated isoforms of transferrin, termed carbohydrate-deficient transferrin (CDT), in relation to the presence of microvascular complications in type 2 diabetes mellitus. We studied 21 patients with type 2 diabetes with microangiopathy and 22 patients without complications who were hospitalized at a diabetic clinic. The prevalence of microvascular complications was based on clinical history, fundoscopy, and laboratory tests. Blood samples were taken for measurements of SA, CDT, total transferrin, glucose, HbA1c, fibrinogen, C-reactive protein (CRP), and indicators of renal dysfunction (i.e., creatinine, urea, albumin excretion rate (AER), and glomerular filtration rate (GFR)). A rise in serum SA and a decrease in CDT concentrations were observed in both diabetic groups with and without complications, and there were no differences between the two groups of patients. There was a statistically significant correlation between serum SA and CDT in diabetic subjects with microvascular complications, but not in patients without such complications. This proves that the serum changes in CDT and SA levels in the course of type 2 diabetes mellitus are associated with each other in the presence of microangiopathy.

Adult↗
PubMed1986

Control of heme synthesis during Friend cell differentiation: role of iron and transferrin.

In many types of cells the synthesis of delta-aminolevulinic acid (ALA) limits the rate of heme formation. However, results from our laboratory with reticulocytes suggest that the rate of iron uptake from transferrin (Tf), rather than ALA synthase activity, limits the rate of heme synthesis in erythroid cells. To determine whether changes occur in iron metabolism and the control of heme synthesis during erythroid cell development Friend erythroleukemia cells induced to erythroid differentiation by dimethylsulfoxide (DMSO) were studied. While added ALA stimulated heme synthesis in uninduced Friend cells (suggesting ALA synthase is limiting) it did not do so in induced cells. Therefore the possibility was investigated that, in induced cells, iron uptake from Tf limits and controls heme synthesis. Several aspects of iron metabolism were investigated using the synthetic iron chelator salicylaldehyde isonicotinoyl hydrazone (SIH). Both induced and uninduced Friend cells take up and utilize Fe for heme synthesis directly from Fe-SIH without the involvement of transferrin and transferrin receptors and to a much greater extent than from saturating levels of Fe-Tf (20 microM). Furthermore, in induced Friend cells 100 microM Fe-SIH stimulated 2-14C-glycine incorporation into heme up to 3.6-fold as compared to the incorporation observed with saturating concentrations of Fe-Tf. In contrast, Fe-SIH, even when added in high concentrations, did not stimulate heme synthesis in uninduced Friend cells but was able to do so as early as 24 to 48 h following induction. In addition, contrary to previous results with rabbit reticulocytes, Fe-SIH also stimulated globin synthesis in induced Friend cells above the level seen with saturating concentrations of transferrin. These results indicate that some step(s) in the pathway of iron from extracellular Tf to protoporphyrin, rather than the activity of ALA synthase, limits and controls the overall rate of heme and possibly hemoglobin synthesis in differentiating Friend erythroleukemia cells.

Aminolevulinic Acid↗
PubMed1989

Maturation-associated loss and incomplete de novo synthesis of the transferrin receptor in peripheral sheep reticulocytes: response to heme and iron.

Hemin, but not iron, in the culture medium stimulates the maturation-associated loss of the transferrin receptor from sheep reticulocytes (t1/2 for loss approximately 6 hr) and its appearance in a population of externalized vesicles. A similar pattern is seen with nucleoside binding (a measure of the nucleoside transporter), where hemin increases the loss of binding activity from the cells during culture, concomitant with an increase in nucleoside binding in the externalized vesicles. Sheep reticulocytes retain the ability to synthesize the transferrin receptor, but the 35S-labeled receptors are not detected in released vesicles. Whereas hemin stimulates the loss of 35S-labeled transferrin receptors from the cell (t1/2 for loss approximately 20 hr), nonheme iron is more effective than heme. This difference in response of native and 35S-labeled receptor to hemin and iron supplements appears to be related to the differences in the two classes of receptors. Although the 35S-labeled receptor binds transferrin and both native and 35S-labeled peptides comigrate after chemical deglycosylation, the 35S-receptor is approximately 2 kD smaller than the native receptor and fails to acquire its complete size even when chased for up to 24 hr. Moreover, the 35S-labeled receptor is not expressed at the cell surface, but is retained in a nonrecycling compartment, where it is insensitive to digestion by trypsin at both 0 degrees C and 37 degrees C.

Animals↗
PubMed1988

Expression of the human transferrin receptor in subrenal capsule assay in the mouse.

The expression of a cell proliferation marker, the human transferrin receptor, was studied in ten human gastrointestinal tumors prior to and after implantation under the renal capsule in the mouse (1-6 days). These data were compared to the increase in tumor size in situ, and to the infiltration of inflammatory cells. All tumors studied expressed the transferrin receptor prior to implantation. Forty of 47 implants expressed the receptor, the strongest expression occurring on day 4, accompanied by a reorganization of tumor tissue to a morphology similar to that before implantation. On days 5 and 6 the expression of the transferrin receptor declined. Implants showed maximal increase in size on days 1 and 2, decreased in size on days 3 and 4, and increased again on days 5 and 6. The increase in the size of the implants on days 5 and 6 was accompanied by considerable infiltration of inflammatory cells, and was probably mostly a result of invading host cells and inflammation. If size alone is used as a criterion for tumor proliferation in this subrenal capsule assay, day 4 seems to be the most appropriate for evaluation. This is supported by a strong expression of a proliferation marker, the human transferrin receptor, during this time.

Animals↗
PubMed1998

Targeting of ultrasmall superparamagnetic iron oxide (USPIO) particles to tumor cells in vivo by using transferrin receptor pathways.

Human transferrin was covalently coupled to ultrasmall superparamagnetic iron oxide (USPIO) particles, and the transferrin-USPIO obtained was investigated in vivo in experimental SMT/2A tumor-bearing rats (rat mammary carcinoma). Physicochemical characterization showed an overall size of 36 nm (DLS) with a core size of 5 nm (TEM). Relaxivities were R1 = 23.6 and R2 = 52.1 liter/mmol.s (0.47 T). Bound transferrin was 280 micrograms/mg of iron. Pharmacokinetic investigations revealed a half-life of 17 min in normal rats. The MR evaluation of tumor signal intensity over time showed a 40% (range 25-55%) signal reduction 150 min after injection with the reduction persisting for at least 8 h. Control experiments using the parent USPIO compound or USPIO labeled with a nonspecific human serum albumin (HSA-USPIO) showed a change of only 10% (range 5-15%) in tumor signal intensity over time. The results demonstrate that a combination of the USPIO relaxivity properties with the specificity of transferrin-mediated endocytosis allows in vivo detection of tumors by MR imaging.

Animals↗
PubMed2000

Circumventing complement C3 interference in the analysis of carbohydrate-deficient transferrin in fresh serum.

A method for preventing interference by the glycoprotein complement C3 and its beta-globulin split products in the capillary electrophoretic analysis of carbohydrate-deficient transferrin was developed. Inulin was used to activate the alternate complement pathway and convert native C3 into various degradation products whose electrophoretic mobility no longer coincides with the transferrin glycoforms. Capillary electrophoresis and zone electrophoresis on agarose gel were used to monitor reaction conditions for alternate complement pathway activation. Incubation of 50 microL of fresh serum with 180 microL of a 50 mg/mL inulin slurry for 12 h removed the native C3 peak from the beta region. Inulin treatment did not affect electrophoretic behavior of other beta-globulins, including transferrin. Altering the electrophoretic behavior of complement C3, by treating fresh serum with inulin, permits rapid capillary electrophoresis evaluation of carbohydrate-deficient transferrin glycoforms.

Artifacts↗
PubMed1995

Inhibitors of phosphoinositide 3-kinase block exocytosis but not endocytosis of transferrin receptors in 3T3-L1 adipocytes.

The role of PI 3-kinase in transferrin receptor recycling was investigated in 3T3-L1 adipocytes. Wortmannin, a specific PI 3-kinase inhibitor, blocked insulin stimulated recruitment of transferrin receptors to the plasma membrane (IC50 approximately 5-15 nM) with a similar potency to its inhibitory effects on PI 3-kinase and glucose transport. Wortmannin also blocked insulin stimulated recruitment of IGF-2 receptors to the cell surface. However, wortmannin (up to 200 nM) and another PI 3-kinase inhibitor, LY294002 (3 micrograms/ml), did not block transferrin receptor endocytosis. This demonstrates that while PI 3-kinase may be necessary for insulin stimulated exocytosis, it is not necessary for endocytosis of transferrin receptors.

3T3 Cells↗
PubMed1995

Transferrin induces nitric oxide synthase mRNA in rat cultured aortic smooth muscle cells.

Incubation with holo-transferrin, but not apo-transferrin, induced the nitrite accumulation in the culture medium of rat aortic smooth muscle cells concentration- and time-dependently, which occurred after a lag period of 6 hours. The accumulation of nitrite was inhibited by N omega-nitro-L-arginine and cycloheximide, but not by calmidazolium. Ferric or ferrous iron had no effect on the accumulation. In reverse transcription-coupled polymerase chain reaction analysis, one amplified fragment (580 bp) corresponding to the inducible form of nitric oxide synthase (iNOS) mRNA was expressed after incubation with holo-transferrin for 10 hours. These results suggest that holo-transferrin activates expression of iNOS mRNA in rat aortic smooth muscle cells accompanied by nitric oxide accumulation via a pathway dependent on L-arginine in the culture medium.

Amino Acid Oxidoreductases↗
PubMedDate not supplied

Mutation analysis of the transferrin receptor-2 gene in patients with iron overload.

Three mutations in the transferrin receptor-2 gene have recently been identified in four Sicilian families with iron overload who had a normal hemochromatosis gene, HFE (C. Camaschella, personal communication). To determine the extent to which mutations in the transferrin receptor-2 gene occur in other populations with iron overload, we have completely sequenced this gene in 17 whites, 10 Asians, and 8 African Americans with iron overload and a C282C/C282C HFE genotype, as well as 4 subjects without iron overload and homozygous for the mutant HFE C282Y genotype, 5 patients with iron overload and homozygous for the mutant HFE C282Y genotype, and 5 normal individuals. None of the individuals exhibited the Sicilian mutations, Y250X in exon 6, M172K in exon 4, and E60X in exon 2. One iron-overloaded individual of Asian descent exhibited a I238M mutation which was subsequently found to be a polymorphism present in the Asian population at a frequency of 0.0192. The presence of the I238M mutation was not associated with an increase in ferritin or transferrin saturation levels. Three silent polymorphisms were also identified, nt 1770 (D590D) and nt 1851 (A617A) and a polymorphism at nt 2255 in the 3' UTR. Thus, mutations in the transferrin receptor-2 gene were not responsible for the iron overload seen in our subjects.

DNA Mutational Analysis↗