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PubMed1993

Cell growth on immobilized cell growth factor: 5. Interaction of immobilized transferrin with fibroblast cells.

Transferrin was immobilized on poly(methyl methacrylate) membrane and the interaction of the immobilized transferrin with mouse fibroblast cells STO was investigated. The immobilized transferrin was stable without decomposition over 48 h and showed higher activities of cell growth acceleration than free transferrin and transported ferric ion as effectively as free transferrin. The specific interaction of the immobilized transferrin with fibroblast cells was confirmed by experiment using the antibody. It was considered that cell growth acceleration and ferric ion transportation occur by different mechanisms.

Animals↗
PubMed1994

Electron paramagnetic resonance and difference ultraviolet studies of Mn2+ binding to serum transferrin.

Serum transferrin is the mammalian protein whose normal function is to transport ferric ions through the blood among sites of absorption, storage, and utilization. It has two specific metal-binding sites that bind a variety of metal ions in addition to ferric ion. The macroscopic equilibrium constant for the binding of the first equivalent of Mn2+ to apotransferrin has been determined by electron paramagnetic resonance spectroscopy (EPR) to be logKM1 = 4.06 +/- 0.13 at pH 7.4 in 0.1 M N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid (Hepes). An equilibrium constant for nonspecific binding of Mn2+ to apotransferrin of logKns = 2.93 +/- 0.13 has also been obtained by using EPR. Binding of Mn2+ to apotransferrin and to both C- and N-terminal nonferric transferrin has also been studied by difference UV spectroscopy. The second stepwise macroscopic equilibrium constant for the formation of Mn2Tf is logKM2 = 2.96 +/- 0.13. The site-specific microconstants for Mn2+ binding are logkN = 3.13 +/- 0.09 for the N-terminal site and logkC = 3.80 +/- 0.09 for the C-terminal site. There does not appear to be any significant cooperativity between the two sites with respect to metal binding. An equilibrium model for the speciation of Mn2+ in serum has been developed which estimates that almost 90% of Mn2+ is bound to serum proteins, but only approximately 1% is bound to transferrin. The weak binding of Mn2+ to apotransferrin and the obvious inability of transferrin to compete with albumin indicates that the appearance of Mn-transferrin as a major serum species in vivo must involve oxidation of the metal to form the much more stable Mn(3+)-transferrin complex. The computer model confirms that albumin has a sufficient binding affinity to complex most of the Mn(II) in serum in competition with the common low molecular weight ligands in serum. However, there is insufficient data to rule out the possibility that some other protein, such as alpha 2-macroglobulin, may compete with albumin for Mn(II).

Animals↗
PubMed1992

A transferrin-independent iron uptake activity in Plasmodium falciparum-infected and uninfected erythrocytes.

Non-heme iron is essential for the asexual growth of the human malaria parasite Plasmodium falciparum in mature erythrocytes. Utilization of iron bound to serum transferrin by the parasitized cells has been postulated, but direct evidence for its specific delivery has not been reported. Here we demonstrate that normal levels of transferrin in human serum are not required for intraerythrocytic P. falciparum growth: culture medium immunodepleted 500-1000 fold in human transferrin was capable of supporting parasitemias and rates of invasion comparable to those observed in non-depleted medium. 55Fe bound to transferrin was not taken up by infected cells. A transferrin-independent non-heme iron uptake activity was, however, detected in both infected and uninfected erythrocytes when iron was presented to the cells as 55Fe-NTA or 55Fe-citrate. Although the uptake activity was not parasite specific, the radiolabel was found in association with parasites mechanically released from the infected erythrocytes, indicating that it is delivered to the intracellular organism. Evidence is presented that the transferrin-independent iron uptake activity is time-, temperature- and concentration-dependent, but apparently not energy-dependent.

Animals↗
PubMed1995

Elevated levels of serum carbohydrate deficient transferrin are not specific for alcohol abuse in patients with liver disease.

BACKGROUND: Serum carbohydrate deficient transferrin is a marker of chronic alcohol consumption; it increases above normal in healthy individuals after a daily alcohol intake of more than 60 g/d for more than 2 weeks. The influence of liver disease itself on carbohydrate deficient transferrin levels has not been sufficiently established. METHODS: We investigated serum levels of carbohydrate deficient transferrin in 196 consecutive patients admitted to our Gastroenterology and Hepatology Unit and correlated this parameter with the patients' statements about alcohol intake during the previous 2 weeks and with other markers of chronic alcohol consumption. RESULTS: In our patient population, carbohydrate deficient transferrin had the best overall performance with respect to sensitivity (88%), specificity (82%), and negative predictive value (98%), as compared to other markers, although specificity was much lower than previously reported in patients without liver disease. In the group of patients with liver disease, sensitivity and specificity were 90% and 73%, respectively, and in patients without liver disease, 80% and 88%. The negative predictive value was excellent (96% for patients with liver disease and 99% for patients without liver disease). CONCLUSIONS: Thus, in a patient with a negative interview for chronic alcohol abuse and normal carbohydrate deficient transferrin level, alcohol is unlikely to be the cause of liver disease, and further investigations to establish the etiology of liver disease are warranted. An increased carbohydrate deficient transferrin level, however, cannot be regarded as reliable evidence for chronic alcohol abuse in patients with liver disease.

Adolescent↗
PubMed1988

Transferrin concentration and location during formation of chick retina: developmental correlates.

The amount of transferrin in chick retina was measured during development and compared to transferrin location seen immunocytochemically. Between embryonic day 6 (E6), and 5 days post hatching, two periods occur in which transferrin concentrations rise sharply and decline. During the first, transferrin concentration rises 5-fold between E6 and 10, then rapidly declines by E14. A second increase begins on E17 and peaks by E19-20. Immunocytochemical findings demonstrate that during the first rise in concentration, transferrin is located primarily in neuritic layers. Later in development, when levels again increase, newly forming photoreceptor outer segments are strongly transferrin positive. These findings are discussed in light of developmental events occurring during retinal maturation.

Animals↗
PubMed1986

Improved purification of the human placental transferrin receptor and a novel immunoradiometric assay for receptor protein.

A simplified method for the purification of human placental transferrin receptor is described. The procedure involves chromatography of a detergent extract of placenta on immobilized iron-loaded transferrin. Knowledge of the physiology of the interaction between transferrin and its receptor is applied to enable bound receptor to be eluted under mild conditions and essentially free of containing transferrin. Purified transferrin receptor and a monoclonal antibody to the receptor were used to develop a novel immunoradiometric assay for the receptor in which the monoclonal antibody is the radiolabelled species. A competition between two populations of receptor, one immobilized on a particulate support and the other in solution, provides the basis for the assay. Using this assay we have measured transferrin receptor levels in placental and hepatic tissue and in three cell lines during both the logarithmic and stationary phases of cell growth.

Antibodies, Monoclonal↗
PubMed1988

The influence of inorganic anions on the formation and stability of Fe3+-transferrin-anion complexes.

Harris (Biochemistry 24 (1985) 7412) reports that inorganic anions bind to human apotransferrin in such a way as to perturb the ultraviolet spectrum. The locus of binding is thought to involve the specific metal/anion-binding sites since no perturbation is observed with Fe3+-transferrin-CO3(2-). Paradoxically, we were unable to demonstrate the formation of Fe3+-transferrin-inorganic anion complexes despite the presence of high concentrations of SO4(2-), H2PO4-, Cl-, ClO4- or NO3-. Similar results were found for human lactoferrin. Electron paramagnetic resonance spectroscopy and visible spectrophotometry were used to monitor the results. An attempt to form the H2PO4- complex by displacement of glycine from Fe3+-transferrin-glycine resulted only in the disruption of the ternary complex. A series of inorganic anions varied in their ability to release iron from Fe3+-transferrin-CO3(2-) at pH 5.5, the approximate pH of endosomes where iron release takes place within cells. The order of effectiveness was H2P2O7(2-) much greater than H2PO4- greater than SO4(2-) greater than NO3- greater than Cl- greater than ClO4-. The rate of iron removal from Fe3+-transferrin-CO3(2-) at pH 5.5 by a 4-fold excess of pyrophosphate was greatly enhanced by physiological NaCl concentration. Iron removal was complete within 10 min, the approximate time for iron release from Fe3+-transferrin-CO3(2-) in developing erythroid cells. Thus, inorganic anions may have a significant effect on the release of iron under physiological conditions despite the fact that such inorganic anions cannot act as synergistic anions. The results are discussed in relation to a special role for the carboxylate group in allowing ternary complex formation.

Anions↗
PubMed1988

Transferrin: an early marker of oligodendrocytes in culture.

In this study, the developmental pattern of transferrin expression, the iron transporting glycoprotein, was investigated morphologically and immunocytochemically in mixed glial cultures as well as pure cultures of mature oligodendrocytes, both derived from newborn rat brain. Double immunofluorescent labeling of pure oligodendrocyte cultures revealed that transferrin co-localizes with the oligodendroglial marker, myelin basic protein. During early development in mixed glial cultures, the presence of transferrin was detected at 3 days in vitro in small round process-bearing cells lying on top of astrocytes. These cells were galactocerebroside negative. However, at 7 days these process-bearing cells began to express galactocerebrosides and transferrin co-localized with the oligodendroglial marker. Transferrin did not co-localize with any neuronal or astroglial markers at any time. These results indicate that transferrin is an oligodendrocyte-specific marker which is expressed earlier than galactocerebroside.

Animals↗
PubMed1993

Erythropoietin and transferrin concentrations during pregnancy in relation to hemoglobin levels.

Serum levels of erythropoietin (EPO) were assayed by ELISA at the same time as red blood cells (RBC), hemoglobin (Hb), hematocrit (Hct), serum iron and transferrin in 136 pregnant women, divided on the basis of hemoglobin values (> or < or = 10.5 g/dl) and weeks of pregnancy (< or > or = 27th week). In the overall population, a parallel increase with weeks of pregnancy was shown by serum concentrations of EPO expressed as a logarithm (multiple R = 0.367, P < 0.0001), and transferrin levels (multiple R = 0.529, P < 0.0001). It was found that EPO levels did not differ significantly between anemic and non-anemic patients before the 27th week, but the difference became highly significant (P < 0.01) after the 27th week in favour of anemic patients. Before the 27th week, the correlations between log EPO and RBC, Hct, Hb and iron were not significant, whereas the correlation between log EPO and transferrin was significant (P < 0.01); after the 27th week, the correlations and significance of the regression found were: log EPO vs Hb (Pearson coefficient = -0.384; P < 0.001), vs Hct (Pearson coefficient = -0.370; P < 0.01), vs transferrin (Pearson coefficient = 0.392; P < 0.0001), vs iron (Pearson coefficient = -0.274, P < 0.05). In the population divided according to Hb levels, the correlation was positive and significant in both groups between log EPO and transferrin (Hb > 10.5 g/dl: Pearson coefficient = 0.524, P < 0.0001; Hb < or = 10.5: Pearson coefficient = 0.614, P < 0.0001), but was inverse and significant only in the group with Hb < or = 10.5 g/dl between log EPO and serum iron (Pearson coefficient = -0.481, P < 0.01). The variations in EPO were related to Hb levels after the 27th week of pregnancy and were closely correlated with transferrin over the whole period. The physiological mechanism of these changes is discussed.

Enzyme-Linked Immunosorbent Assay↗
PubMed1991

Sandwich enzyme immunoassay for rat transferrin with two monoclonal antibodies and its application.

The development of a sandwich enzyme immunoassay for rat transferrin with two monoclonal antibodies is described. Microtiter plates coated with one monoclonal antibody (15C2H3) were used, and captured transferrin was estimated with a horseradish peroxidase-conjugated Fab' fragment of another monoclonal antibody (22A06D2). In this assay, the measurable range is 5-150 ng/ml and the coefficients of variation within and between the assay series are 1.2-5.0 and 3.3-6.0%, respectively. Recovery was 101 +/- 9.7% when purified rat transferrin was added to rat plasma. No cross-reactivity with bovine, human, or mouse transferrin was shown. This assay for rat transferrin is a highly specific, sensitive, and expeditious method which may allow routine analysis of rat transferrin in blood or culture supernatants of rat hepatocytes.

Animals↗
PubMed2006

Determination of carbohydrate-deficient transferrin in human serum using the Bio-Rad %CDT by HPLC test.

BACKGROUND: Carbohydrate-deficient transferrin (CDT) in serum is a biomarker used to identify individuals with sustained, heavy alcohol consumption. This study evaluated the performance of a new commercial method for CDT, the Bio-Rad %CDT by HPLC test, that measures relative amounts of separate transferrin glycoforms in proportion to total transferrin. METHOD: The samples used were two human serum pools (low/high disialotransferrin), 150 clinical sera with low to highly elevated disialotransferrin values, and 18 genetic transferrin variants. Glycoforms are separated on a gradient HPLC system, followed by specific measurement of the iron-transferrin complex at 460 nm. Comparison was made with an HPLC candidate reference method on an Agilent 1100 LC system. RESULTS: The Bio-Rad %CDT by HPLC test allowed for reproducible separation and quantification of the transferrin glycoforms within approximately 6 min. Genetic variants were readily identified. For the low and high serum pool, the total CV was 8.5% and 4.3%, respectively. The relative amounts of disialotransferrin, the main CDT glycoform, were in good agreement with the results of the HPLC candidate reference method (r(2)=0.998, p<0.0001). CONCLUSIONS: The present results demonstrated that the Bio-Rad %CDT by HPLC test is appropriate for confirmatory and routine %CDT testing in human serum, with the added advantage over previously published HPLC methods of an improved serum sample pretreatment and a shorter total analysis time.

Alcoholism↗
PubMed2006

Lens epithelial cells synthesize and secrete ceruloplasmin: effects of ceruloplasmin and transferrin on iron efflux and intracellular iron dynamics.

Although an essential nutrient, iron can catalyze damaging free radical reactions. Therefore elaborate mechanisms have evolved to carefully regulate iron metabolism. Ceruloplasmin, a protein with ferroxidase activity, and transferrin, an iron binding protein have important roles in maintaining iron homeostasis in cells. Since oxidative damage is a hallmark of cataractogenesis, it is essential to determine iron's role in lenticular physiology and pathology. In the current study of lens epithelial cells, the effects of ceruloplasmin and transferrin on intracellular distribution and efflux of iron were determined. Both ceruloplasmin and transferrin increased iron efflux from these cells and their effects were additive. Ceruloplasmin had significant effects on extracellular iron distribution only in cases of iron overload. Surprisingly, both transferrin and ceruloplasmin had significant effects on intracellular iron distribution. Under physiological conditions, ceruloplasmin increased iron incorporation into the storage protein, ferritin. Under conditions of iron overload, it decreased iron incorporation into ferritin, which is consistent with increased efflux of iron. Measurements of an intracellular chelatable iron pool indicated that both transferrin and ceruloplasmin increased the size of this pool at 24 h, but these increases had different downstream effects. Finally, lens epithelial cells made and secreted transferrin and ceruloplasmin. These results indicate an important role for these proteins in iron metabolism in the lens.

Animals↗
PubMed2003

Synthesis and secretion of transferrin by isolated ciliary epithelium of rabbit.

It has been shown that the vitreous contains several intrinsic glycoproteins whose origin remains to be clarified. Isolated ciliary epithelium (CE) was assayed to verify its role in the synthesis and secretion of transferrin for the vitreous body. It was cultured in the presence of [35S]methionine and the incubation medium was processed for immunoprecipitation. Total RNA from CE was processed for RT-PCR and the amplification products were sequenced. Also, whole preparations of isolated CE were processed for immunolocalization of transferrin. From the incubation assays, a labeled peptide of about 80 kDa was immunopurified that is the expected size of transferrin. The RT-PCR and sequencing experiments detected the presence of transferrin mRNA. Both layers of the CE exhibited transferrin reactivity, following immunohistochemical processing. Taken altogether, these results indicate the CE as one of the possible sources of vitreous intrinsic transferrin.

Animals↗
PubMed1995

Transferrin secretion by lens epithelial cells in culture.

Transferrin (Tf), the plasma iron transport protein which supports cell proliferation and differentiation and has bacteriostatic, antioxidant and anti-inflammatory activity, has been found in relatively high concentrations in the intraocular fluids. Intraocular synthesis of Tf has recently been demonstrated, although the intraocular tissue(s) responsible have not been identified. We designed this study to determine whether certain ocular tissues can make and secrete transferrin. Transferrin content of aqueous and vitreous humors and whole lenses was determined by ELISA. Transferrin secretion by cultured epithelia from lens and ciliary body was also measured. In addition, Northern blots of RNA from cultured lens epithelial cells, ciliary body pigmented and non-pigmented epithelial cells, and from whole iris, ciliary body and retina were probed with riboprobes for Tf mRNA and 18S rRNA. Transferrin made up 23% and 16% of total canine aqueous and vitreous protein. All ocular tissues and cultured cells tested contained mRNA for Tf, however Tf was secreted into the bathing medium from lens epithelial cell cultures, but not from either the pigmented or non-pigmented epithelial cells of the ciliary body cultures, but not from either the pigmented or non-pigmented epithelial cells of the ciliary body Cycloheximide inhibited secretion of Tf from the lens epithelial cells. Lenses from inflamed eyes contained higher levels of Tf than their contralateral controls. This is the first experimental demonstration that an intraocular tissue can make and secrete Tf. Transferrin secretion by the lens may contribute significantly to the IOF content of this important intraocular protein.

Animals↗
PubMed1985

Ceruloplasmin and transferrin in human seminal plasma: are they an index of seminiferous tubular function?

Transferrin and ceruloplasmin have been measured by a solid-phase chemiluminescent method in seminal fluid and circulating blood of normal and vasectomized subjects (1 year after operation). This study has confirmed that approximately 80% of seminal transferrin comes from the testis, while seminal ceruloplasmin was not found different in the two groups. In patients affected by azoospermia due to seminiferous tubular damage (n = 15) in whom an obstruction was previously excluded, seminal transferrin was always below the normal range. On the contrary, seminal ceruloplasmin was always in the normal range, and circulating follicle-stimulating hormone was found above the normal range only in nine cases. No correlation was found between seminal transferrin and circulating follicle-stimulating hormone in such groups. In an unselected group of infertile patients with decreased sperm concentration and/or sperm motility, seminal transferrin was found correlated with the sperm count. These studies seem to suggest that seminal transferrin is a reliable index of seminiferous tubular function.

Ceruloplasmin↗
PubMed2000

Detection by ELISA of low transferrin levels in bronchoalveolar secretions of preterm infants.

Transferrin levels in bronchoalveolar secretions (BAS) are very low compared to serum levels in humans. For the exact measurement of transferrin concentrations in BAS a very sensitive assay was developed as a double sandwich enzyme immunoassay using the combination of a polyclonal and a monoclonal antibody against human transferrin. The measurable range of the assay was 1.5 to 100 ng/ml of human transferrin. The lowest measurable value was 0.84 ng/ml and the sensitivity of the assay was 0.88 ng/ml. The coefficient of variation was 14.1% for 25 ng/ml (intra-assay) and 11-20% (inter-assay). The levels measured in 123 samples of BAS of preterm infants ranged between 0.03 and 8.93 (microgram/microgram secretory component (SC)). The determination of transferrin in BAS of preterm infants is helpful in determining oxidative damage, e.g. the availability of free iron, in the neonatal lung. The transferrin concentration in BAS of neonates who recovered from respiratory distress syndrome (RDS) in the first six days of life was 0.48 compared to 0.52 ((microgram/microgram SC), median range) for infants who developed chronic lung disease.

Antibodies, Monoclonal↗
PubMed1984

Glycosylated albumin and transferrin: short-term markers of blood glucose control.

Serum was collected from children with type 1 diabetes mellitus before and 10 days after attending a camp session in which blood glucose concentrations were carefully controlled. Glycosylated and nonglycosylated proteins were separated, and levels of albumin and transferrin were determined on each of these fractions. Glycosylated hemoglobin was also determined and ranged from 4.6% to 14.6% (mean +/- SEM 8.1% +/- 0.2%). Mean initial glycosylated albumin in 73 children was 16.4% +/- 0.6%, which was elevated compared with the mean of levels in 20 nondiabetic controls (8.7% +/- 0.3%) and correlated well with levels of glycosylated hemoglobin (r = 0.71). After 10 days mean glycosylated albumin fell to 14.6% +/- 0.5% (P less than 0.00001), near the predicted final value of 13.4% if control had been ideal. Initial levels of glycosylated transferrin in 44 of these children ranged from 4.5% to 22.3% (11.4 +/- 0.6%) and was significantly higher than the mean of 3.8% +/- 0.3% in 20 nondiabetic controls. Mean final glycosylated transferrin fell to 8.2% +/- 0.3% (P less than 0.00001), near the predicted final mean of 7.0% +/- 0.2%. The mean of each subject's blood glucose determinations performed throughout the study period correlated with final levels of both glycosylated albumin (r = 0.55, P less than 0.001) and glycosylated transferrin (r = 0.54, P less than 0.001). Both glycosylated albumin and glycosylated transferrin appear to be reliable markers of short-term glycemic control; glycosylated transferrin (half-life 8 days) was more sensitive than glycosylated albumin over this 10-day period.

Adolescent↗
PubMed1980

Quantitative estimation of abnormal microheterogeneity of serum transferrin in alcoholics.

A qualitative abnormality of the microheterogeneity of serum transferrin, demonstrated by isoelectric focusing, has previously been shown to be a highly specific indication of chronic alcoholism. The abnormality consists of a selective increase of a cathodal transferrin component which is probably caused by a reduction of the sialic acid content. The present study describes a method for quantitative estimation of the abnormal transferrin. The technique was based on analytical isoelectric focusing as the first step followed by direct immunofixation. The immunofixed transferrin was quantified by computerized on-line densitometry, and the transferrin abnormality was calculated as a quotient, where the amount of the cathodal component was expressed as a percentage of the relative total immunofixed transferrin quantity. This method was shown to possess high sensitivity and good reproducibility. In the controls the mean value of the quotient was 3.7%, while in the alcoholics it was 9.5% which was a highly significant difference (p less than 0.001). The possible functional significance of a disturbed sialic acid metabolism in alcoholism is discussed.

Adult↗