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PubMed2000

[Diagnosis of iron deficiency: evaluation of the "soluble transferrin receptor/transferrin" ratio].

OBJECTIVE: This study was aimed at determining the diagnostic value of conventional laboratory tests regarding the iron status and serum transferrin receptor in hospitalized patients. METHODS: Patients who had to undergo bone marrow aspirate examination were included in this 8-month prospective study. Iron deficiency was defined as the absence of stainable iron on bone marrow examination. Patients with stainable iron were included in the control group. The higher value of diagnostic efficacy determined the cut-off value for each parameter of the iron status. RESULTS: Twenty-one patients (17 females, four males) (mean age: 52 years) with iron deficiency and 33 control subjects (20 females, 13 males) (mean age: 60 years) were included in the study. The ratio serum transferrin receptor/serum ferritin had the best diagnostic efficiency (78%) with a sensitivity of 81% and a specificity of 97%. Serum ferritin alone with a cut-off value of 60 micrograms/L had the same specificity (97%) but a lower sensitivity (76%). The diagnostic value of all other analyzed tests was below 66% (transferrin alone, mean corpuscular volume, transferrin saturation, iron, serum transferrin receptor alone, red cell distribution width). CONCLUSION: Among in-patients, ferritin remains the first intention test to diagnose iron deficiency, but the cut-off value should be increased (60 micrograms/L in this study). The ratio "serum transferrin receptor to serum ferritin" provides the highest specificity with a higher cost and should be used only in doubtful cases.

Anemia, Iron-Deficiency↗
PubMed1993

The association of non-insulin-dependent diabetes mellitus and hypertension with urinary excretion of albumin and transferrin.

Abnormal urinary excretion of albumin is a nonspecific sign of nephropathy, commonly occurring in persons with hypertension as well as diabetes. Transferrin, rather than albumin, is more readily excreted by the kidney in those with diabetes compared with those with hypertension alone. One hundred eighty non-insulin-dependent diabetic mellitus patients were age, race, and sex matched to 90 nondiabetic control subjects who had mild to moderate hypertension. Overnight urine collections were analyzed by immunoturbidity for albumin and transferrin. The average duration of hypertension was 11 years among controls. Mean blood pressures were 134/79 mm Hg for diabetic subjects and 145/87 mm Hg for controls (P < 0.001). Diabetic patients had higher mean excretion rates of albumin (128 micrograms/min v 49 micrograms/min; P = 0.04) and transferrin (7.3 micrograms/min v 0.9 microgram/min; P = 0.0001) and higher excretion ratios of albumin (0.179 g/g creatinine v 0.069 g/g creatinine; P = 0.02) and transferrin (0.0065 g/g creatinine v 0.0013 g/g creatinine; P < 0.001) than hypertensive controls. Ratios of transferrin to albumin excretion for those with diabetes and hypertension greatly exceeded expected ratios for those with hypertension or diabetes alone if the effects of these disorders were additive. While diabetic patients were twice as likely as controls to have abnormal albumin excretion ratios (P = 0.01), they were three times as likely to have elevated transferrin excretion ratios (P = 0.0001), even though the diabetic group was half as likely as the controls to have systolic blood pressure > or = 160 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1998

Identification of carbohydrate deficient transferrin forms by MALDI-TOF mass spectrometry and lectin ELISABiochim Biophys Acta 1998 Aug 24;1381(3):356.

Transferrin was isolated from sera of patients with severe alcohol abuse and from control sera by affinity chromatography using an immobilized polyclonal antibody from sheep, followed by gel filtration. The purified transferrin was then separated by MonoQ chromatography. Compared to the controls, sera from heavy alcohol consumers showed two additional transferrin peaks, eluting earlier than the three main transferrin forms present in all sera. Further analysis of the isolated transferrin forms by matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) and enzyme linked immunosorbent assay with different digoxigenylated lectins (lectin ELISA) revealed that the main carbohydrate deficient transferrin (CDT) forms are lacking either one or both of the N-Glycan chains.

Alcoholism↗
PubMed2000

The rat visceral yolk sac internalizes maternal transferrin and secretes hydrolyzed products towards the fetus.

The uptake of transferrin by the rat visceral yolk sac membranes, and the fate of this protein, were measured in a two-chambered system which allowed access to both surfaces of these membranes, i.e. that facing the maternal compartment and that facing the fetal compartment. 125I-labeled transferrin was internalized by the maternal surface of the visceral yolk sac but not by the fetal surface. Following internalization, this transferrin was degraded and the amino acids were secreted exclusively towards the fetal compartment. Transcytosis of intact transferrin was not detected in either direction. These results suggest that transport across the rat visceral yolk sac bound to maternally derived transferrin is not a major mechanism of iron transport in vivo. These results support a role for the visceral yolk sac in fetal metabolism, or supplying the fetus with amino acids derived from degradation of specific maternal plasma proteins, in this case, transferrin.

Animals↗
PubMed2005

Carbohydrate-deficient transferrin and gamma-glutamyl transpeptidase in the evaluation of alcohol consumption. A five-year retrospective study of 633 outpatients in a single center.

OBJECTIVE: Carbohydrate-deficient transferrin has been proposed to be useful in evaluating alcohol consumption but there is no consensus on its use in routine practice. The aim of this retrospective study was to compare carbohydrate-deficient transferrin and gammaglutamyl transpeptidase assays for the evaluation of alcohol consumption. METHODS: Six hundred thirty-three outpatients attending one outpatient care center were included in this study. Patients were divided into five categories according to alcohol consumption: category 1 included non-weaned patients drinking more than 30 g/day for women and more than 50 g/day for men, category 2 included relapse patients, category 3 included moderate drinkers, category 4 included patients weaned less than one month, and category 5 included patients weaned more than one month. One experienced physician estimated alcohol intake from patient declarations during a face-to-face interview. RESULTS: Sensitivity of carbohydrate-deficient transferrin varied, depending on patient category, from 32% to 92% versus 41% to 72% for gamma-glutamyl transpeptidase. Specificity of carbohydrate-deficient transferrin varied from 71% to 96% versus 23% to 62% for gamma-glutamyl transpeptidase. After one month of abstinence, specificity of carbohydrate-deficient transferrin was 62% versus 19% for gamma-glutamyl transpeptidase. CONCLUSION: This study confirms that carbohydrate-deficient transferrin is more accurate in predicting alcohol consumption compared with gamma-glutamyl transpeptidase in alcoholic outpatients.

Adult↗
PubMedDate not supplied

Carbohydrate-deficient transferrin in the ethanol-consuming rat model.

Regular ethanol consumption leads to the appearance of carbohydrate-deficient transferrin in the plasma of human subjects. The mechanism for this finding remains uncertain. We have exposed female Wistar rats to ethanol from 3 weeks of age to 22 weeks and have studied transferrin in these animals. Isoelectric focusing (IEF) of serum identified two additional transferrin forms in the ethanol-exposed rats. Routine staining and immunofixation demonstrated transferrin focused at pH 5.45 and 5.65. Neuraminidase-treated normal rat serum focused in 2 bands at pH 5.85 and 6.15 corresponding to the additional bands in ethanol-treated rats. Human transferrin exposed to neuraminidase focused at pH 5.7 as described by others. The results suggest that the rat may be used as an animal model to study the complex effects of ethanol on transferrin and iron metabolism.

Alcohol Drinking↗
PubMed2004

How useful is glucose detection in diagnosing cerebrospinal fluid leak? The rational use of CT and Beta-2 transferrin assay in detection of cerebrospinal fluid fistula.

BACKGROUND: This report describes the sensitivity and specificity of glucose detection using Glucostix test strips and computed tomography (CT) of the skull base for confirming cerebrospinal fluid (CSF) fistulae in patients with persistent rhinorrhoea or otorrhoea, and comparing them with the beta-2 transferrin assay as the gold standard for CSF detection. METHODS: Fluid samples from the nose were collected from 18 patients with suspected CSF fistulae. The samples were assayed for beta-2 transferrin using the Western blotting and immunostaining technique. CT (5mm axial slice) of the skull base was performed for evidence of skull base fracture. The glucose levels and Glucostix results were compared. RESULTS: Out of the 18 samples, 15 were positive for beta-2 transferrin adn the leaks were validated surgically in 10 patients. Give leaks healed spontaneously with conservative management. Glucostix tests produced three false positive results from blood and nasal mucus contaminated fluid. Glucostix failed to detect another three CSF leaks resulting from false negative tests because of low CSF glucose levels. The Glucostix glucose test was nonspecific and insensitive compared with the beta-2 transferrin assay. CT failed to detect three of the 15 beta-2 transferrin-positive leaks but there were no false positive results. CT produced six negative results, of which three were false negatives. CONCLUSIONS: Glucose detection using Glucostix test strips is not recommended as a confirmatory test due to its lack of specificity and sensitivity. In the presence of a skull bas fracture on CT and a clinical CSF leak, there is no need for a further confirmatory test. In cases where a confirmatory test is needed, the beta-2 transferrin assay is the test of choice because of its high sensitivity and specificity.

Cerebrospinal Fluid Otorrhea↗
PubMed2003

Mass spectrometric characterization of transferrins and their fragments derived by reduction of disulfide bonds.

Mass spectrometry, proteomics, and protein chemistry methods are used to characterize the cleavage products of 79 kDa transferrin proteins induced by iron-catalyzed oxidation, including a novel C-terminal polypeptide released upon disulfide reduction. Top-down electrospray ionization tandem mass spectrometry (ESI-MS/MS) of intact multiply-charged transferrin from a variety of species (human, bovine, rabbit, chicken) performed on a quadrupole time-of-flight mass spectrometer yields multiply-charged b(n)-products originating near residues 56-69 from the N-terminal region, in addition to their complementary y(n)-products. Incubation of transferrin with reductants, such as dithiothreitol (DTT) or tris(2-carboxyethyl)-phosphine (TCEP), yields an increase in multiple charging observed by ESI-MS and an increase in molecular weight consistent with disulfide reduction. However, mammalian transferrins release a 6-8 kDa fragment upon disulfide reduction. Protein acetylation and MS/MS sequencing demonstrate that the fragment originates from the C-terminus of the protein, and that it is a separate polypeptide linked via three disulfide bonds to the main transferrin chain. The existence of a separate C-terminal chain is not annotated in protein sequence databases and, to date, has not been reported in the literature. Iron-catalyzed cleavage induces fragments originating from both the N- and C-terminus of transferrin.

Amino Acid Sequence↗
PubMed2003

The significance of transferrin receptor variation in Trypanosoma brucei.

The transferrin receptor of Trypanosoma brucei is encoded by genes located in different expression sites. The various expression sites encode slightly different transferrin receptors, which differ substantially in their affinity for transferrin of different host species. It was proposed that T. brucei has developed multiple expression sites encoding different transferrin receptors not only to cope with the diversity of mammalian transferrins, but also to ensure sufficient iron uptake in the presence of anti-transferrin receptor antibodies. This article shows that calculations based on K(d) values argue against the first part of the hypothesis, but might support the second part.

Animals↗
PubMed1980

Characterization of transferrin metal-binding sites by diffusion-enhanced energy transfer.

The distance from the protein surface to ferric or manganic ions in the two specific metal-binding sites of human serum transferrin has been estimated by measuring energy transfer from freely diffusing terbium chelaters in aqueous solution to transferrin-bound metal ions. In addition, both monoferric forms of the protein were studied, as well as the diferric complex formed by using oxalate instead of (bi)carbonate as the auxiliary anion in binding of iron(III) to transferrin. Second-order rate constants for energy transfer between electrically neutral terbium(III)--N-(2-hydroxy-ethyl)ethylenediaminetriacetate and the FeA, FeB, and Fe2 forms of transferrin were 0.9 X 10(5) M-1 S-1, 1.4 X 10(5) M-1 S-1, and 2.6 X 10(5) M-1 S-1, respectively (based on iron concentraton). For the Fe2 species, substitution of oxalate for (bi)carbonate has the effect of decreasing the accessibility of both electrically neutral and negatively charged terbium chelates to the protein-bound iron chromophores. Theoretical considerations of the effect of acceptor location in the protein on energy transfer suggest that the iron chromophores are not on the surface of the protein but are less than 1.7 nm below the surface. The use of diterbium transferrin as energy donor to a small cobalt chelate in solution or to diferric transferrin corroborates these results.

Binding Sites↗
PubMed1978

Factors affecting the adenosine triphosphate induced release of iron from transferrin.

The release of iron from transferrin was investigated by incubating the diferric protein in the presence of potential iron-releasing agents. The effective chemical group appears to be pyrophosphate, which is present in blood cells as nucleoside di- and triphosphates, notably adenosine triphosphate (ATP). An alternative structure with comparable activity is represented by 2,3-diphosphoglycerate. Neither 1 mM adenosine monophosphate (AMP) nor 1 mM orthophosphate released iron from transferrin. The ATP-induced iron-releasing activity was dependent on weak acidic conditions and was sensitive to temperature and sodium chloride concentration. The rate of iron release rapidly increased as transferrin was titrated with HCl from pH 6.8 to 6.1 in the presence of 1 mM ATP and 160 mM NaCl at 20 degrees C. Iron release from transferrin without ATP was observed below pH 5.5. Ascorbate (10(-4) M) reduced Fe(III), but only after iron release from transferrin by a physiological concentration of ATP. A proposal for the mechanism of iron release from transferrin by ATP and the utilization of reduced iron by erythroid cells is described.

Adenosine Triphosphate↗
PubMed1978

Iron exchange between ferritin and transferrin in vitro.

The transfer of iron between horse spleen [55Fe]ferritin and human apotransferrin or [59Fe]transferrin in homogeneous solution was investigated. Transfer between the two proteins in the presence of citrate, ATP, or ascorbate occurs in both direction, but the net flow is always from ferritin to transferrin. Ferritin which is ca. 1/3 to 1/2 saturated with iron appears to be most reactive. Chemically prepared apoferritin does not accept iron from diferric transferrin. Citrate-mediated transfer of iron from ferritin to apotransferrin is first order with respect to ferritin, zero order with respect to transferrin, and has a complex dependence upon citrate concentration. Direct transfer of iron from native or reconstituted ferritin to apotransferrin in the absence of any identifiable mediating agent was observed to occur at about half the rate attained in the presence of 1 mM citrate. No transfer of iron between the two proteins occurs across a dialysis membrane in the absence of a mediating agent. No binding of transferrin and ferritin to each other was demonstrable. One possible explanation for these observations is that iron from the core of ferritin is in equilibrium with iron near the outer surface of the protein, where the metal would be available to transferrin.

Animals↗
PubMedDate not supplied

Insulin-like growth factor-I and transferrin mediate growth and survival of Chinese hamster ovary cells.

The aim of this investigation was to elucidate the roles of insulin-like growth factor-I (IGF-I) and transferrin in the survival and proliferation of Chinese hamster ovary (CHO) cells upon withdrawal of serum. For this purpose, we employed DNA analysis and flow cytometry to compare CHO cell lines expressing either IGF-I alone or IGF-I and transferrin. The ability of cells to cycle and the occurrence of apoptosis were monitored in these cells in serum-free medium. These results indicate that IGF-I alone is able to maintain the viability of CHO cells for an extended length of time in the absence of serum. Transferrin alone does not promote survival or proliferation. Only in the presence of both IGF-I and transferrin do cells survive and proliferate. Therefore, in attached CHO cultures, IGF-I alone does not stimulate cell proliferation but is a requirement for growth in serum-free medium in cooperation with transferrin. We report on the dual role of IGF-I as a survival factor in CHO cells and its interlocking role with transferrin to stimulate cell growth.

Animals↗
PubMed2005

Ti(IV) binds to human serum transferrin more tightly than does Fe(III).

The binding of titanium(IV) to human serum transferrin in 50 mM Tris with 20 mM bicarbonate and 10 mM citrate at pH 7.4 was studied by UV/vis kinetics and by isothermal titration calorimetry. Ti(IV) citrate, [Ti(C6H4O7)3]8-, employed in this study was previously characterized and delivers the metal to transferrin rapidly, allowing the quantification of the intrinsic binding constants for Ti(IV) to the C- and N-sites of transferrin. The results after correcting for blood plasma conditions (pH 7.4, [HCO3-] = 27 mM) reveal that Ti(IV) binds with greater affinity (log K = 26.8 and 25.7) than Fe(III) (log K = 22.5 and 21.4) to transferrin, a finding not previously observed for other examined metal ions. The strength of metal binding to transferrin correlates with the Lewis acidity of the metal. Ti(IV) is more Lewis acidic than Fe(III) and is nearly the same size. The study also reveals that Ti(IV) binds more tightly to one site than the other, and this difference is due to both entropic and enthalpic contributions. The study has implications for the role of transferrin in the anticancer activity of Ti(IV) drugs and the serum binding of Ti(IV) ions released from implants or imaging reagents.

Binding Sites↗
PubMed2000

Glycosylation of transferrin in Alzheimer's disease and alcohol-induced dementia.

Transferrin is a glycosylated metal-binding serum protein. Carbohydrate-deficient transferrin (CDT) is a marker of recent and heavy alcohol intake. A genetic variant of transferrin, TfC2, occurs with increased frequency in patients with Alzheimer's disease (AD). Hence the question arose whether, in addition to an altered amino acid sequence, there could also be a difference in the glycosylation state of transferrin in patients with dementia. Serum samples of 37 AD and 13 Alcohol-induced dementia patients as well as 10 healthy controls were analyzed for abnormal Tf variants, using isoelectric focusing followed by blotting with anti-Tf antibodies. This allowed the direct visualization of glycosylation variants of transferrin, and assessment of any increase in underglycosylated forms (di-, mono- and asialo transferrin).

Adult↗
PubMed1999

Butyrylcholinesterase is complexed with transferrin in chicken serum.

The function of the enzyme butyrylcholinesterase (BChE) both in serum and in brain is unclear. In serum, BChE has been found complexed with several biomedically relevant proteins, with which it could function in concert. Here, the existence of a similar complex formed between BChE and sero-transferrin from adult chicken serum was elucidated. In order to identify both proteins unequivocally, we improved methods to highly purify the 81-kDa BChE and the coisolated 75-kDa transferrin, which then allowed us to tryptically digest and sequence the resulting peptides. The sequences as revealed for BChE peptides were highly identical to mammalian BChEs. A tight complex formation between the two proteins could be established (a) since transferrin is coisolated along with BChE over three steps including procainamide affinity chromatography, while transferrin alone is not bound to this affinity column, and (b) since imunoprecipitation experiments of whole serum with a transferrin-specific antiserum allows us to detect BChE in the precipitate with the BChE-specific monoclonal antibody 7D11. The possible biomedical implications of a complex between transferrin and BChE which here has been shown to exist in chicken serum are briefly discussed.

Amino Acid Sequence↗
PubMed2000

Assessment of iron status using plasma transferrin receptor in pregnant women with and without human immunodeficiency virus infection in Malawi.

BACKGROUND: Although anemia is highly prevalent during pregnancy and is common during human immunodeficiency virus (HIV) infection, anemia and iron status have not been well characterized in HIV-infected pregnant women. OBJECTIVE: To gain insight into iron status in HIV-infected pregnant women using plasma transferrin receptor and related indicators of anemia. STUDY DESIGN: Plasma transferrin receptor, ferritin, alpha1-acid glycoprotein, C-reactive protein and hemoglobin concentrations were measured in pregnant women, gestational age 18-28 weeks, seen in an urban antenatal clinic in Blantyre, Malawi. RESULTS: The prevalence of anemia among 662 HIV-positive and 190 HIV-negative pregnant women was 73.1% and 50.0%, respectively (P<0.0001). Among HIV-positive and HIV-negative women, median plasma transferrin receptor concentrations were 24.4 and 24.1 nmol/l (P=0.5), respectively, and median plasma ferritin concentrations were 17.8 and 20.8 microg/l (P<0.05), respectively. There was a large overlap in plasma transferrin receptor concentrations among women with and without anemia. Using the combination of hemoglobin and ferritin as a standard, the sensitivity and specificity of plasma transferrin receptor in diagnosing iron deficiency anemia was estimated at 45.9% and 68.1%, respectively. CONCLUSION: The use of plasma transferrin receptor concentrations as an indicator of iron deficiency anemia may be limited in pregnant women with chronic inflammation and infection.

Adult↗
PubMed2003

Rab5 and Rab11 mediate transferrin and anti-variant surface glycoprotein antibody recycling in Trypanosoma brucei.

The mammalian-infective bloodstream form of Trypanosoma brucei possesses a highly active endocytotic system. Evasion of the host immune response by T. brucei is dependent on antigenic variation of VSG (variant surface glycoprotein), but additional mechanisms for removal of surface-bound antibody also operate. Four Rab proteins, Tb (trypanosomal) RAB4, 5A, 5B and 11 are located to the endosomal system; TbRAB5A and TbRAB11 co-localize with internalized anti-VSG antibody and transferrin. A live cell assay was used to record a single cycle of endocytosis of anti-VSG IgG and transferrin, their subsequent degradation within the endosomal system and exocytosis of the products. TbRAB5A and TbRAB11 were involved in the overall process of endocytosis, degradation and exocytosis, whereas TbRAB5B and TbRAB4 were not implicated. The kinetics of anti-VSG IgG and transferrin recycling depend on the nucleotide state of TbRAB5A and TbRAB11. These data, together with previous work, suggest that IgG and transferrin initially enter a TbRAB5A sorting endosome and are most probably recycled subsequently via a TbRAB11-dependent step. Analysis of the recycled IgG and transferrin demonstrated extensive degradation of these recycled proteins. Degradation of transferrin was enhanced in cells expressing increased amounts of TbRAB5A or TbRAB11 with a Ser-->Asn mutation, but was decreased when active TbRAB11 was overexpressed. The extent of degradation of anti-VSG IgG was found to be unaffected by mutant Rab protein expression. The presence of an efficient mechanism for the removal of IgG bound to the external surface of T. brucei and its subsequent proteolysis within the recycling system suggests a role for this pathway in immune evasion.

Animals↗