Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Transferrin”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources
PubMed1994

Iterative endocytosis of transferrin by K562 cells.

The effect of iron on the exocytosis of transferrin by K562 cells was studied by first allowing the cells to endocytose apotransferrin or diferric transferrin. Subsequent release of the apotransferrin was very rapid with a t 1/2 of 3.01 min, compared with 5.5 min for diferric transferrin. Release of apotransferrin was slowed by the weak base methylamine, t 1/2 8.0 min, but the effect of this agent was substantially greater when iron-transferrin was used, t 1/2 18.65 min, suggesting that methylamine affects both iron removal and receptor recycling. Release of iron-transferrin could be accelerated to a rate comparable with that of apotransferrin by addition of the permeant iron-chelator desferrioxamine. The difference in the rates of release of different forms of the protein could be explained by the re-endocytosis of the iron-rich protein, a process detected by the accelerated release of transferrin when the cells were washed in medium at pH 5.5 containing an iron-chelator or treated with a protease-containing medium to digest transferrin accessible at the cell surface. It appears that in cells incubated under control conditions, re-endocytosis of transferrin, which is incompletely depleted of iron, occurs and that a transferrin molecule may make two passes through the cell before all the iron is removed. This mechanism helps to explain why very little iron-transferrin is released from cells and why the efficiency of the iron uptake process is so high.

Cells, Cultured↗
PubMed2002

Non-transferrin-bound iron in untreated and ribavirin-treated chronic hepatitis C patients.

BACKGROUND: In patients with chronic hepatitis C, elevations in serum iron levels, hepatic iron content and oxidative stress-related molecules have been reported. Treatment with ribavirin induces an increase in hepatic iron concentration. In situations of iron overload, non-transferrin-bound iron can appear. Therefore, we determined non-transferrin-bound iron levels in untreated chronic hepatitis C patients and in patients during interferon-ribavirin treatment. MATERIALS AND METHODS: In 10 untreated and 19 interferon-ribavirin-treated chronic hepatitis C patients, we examined non-transferrin-bound iron levels by a colorimetric method using nitrilotriacetic acid as a ligand and sodium triscarbonatecobalt (III) to block free iron binding sites on transferrin. RESULTS: Despite the presence of high serum iron saturation and ferritin levels, non-transferrin-bound iron was absent in the majority of hepatitis C virus patients (25/29, 86%). There was no difference in non-transferrin-bound iron levels between untreated and treated patients. Four patients with high non-transferrin-bound iron levels were distinguished by higher serum iron levels. In two of these patients, hepatocytic iron was present on liver biopsy. CONCLUSIONS: In the majority of chronic hepatitis C patients, non-transferrin-bound iron levels are normal. Treatment with ribavirin does not induce high non-transferrin-bound iron levels. Non-transferrin-bound iron levels are only higher than normal in hepatitis C patients with higher serum iron levels.

Adult↗
PubMed2002

Complexation of ytterbium to human transferrin and its uptake by K562 cells.

There is an increasing interest in the use of lanthanides in medicine. However, the mechanism of their accumulation in cells is not well understood. Lanthanide cations are similar to ferric ions with regard to transferrin binding, suggesting transferrin-receptor mediated transport is possible; however, this has not yet been confirmed. In order to clarify this mechanism, we investigated the binding of Yb3+ to apotransferrin by UV-Vis spectroscopy and stopped-flow spectrophotometry, and found that Yb3+ binds to apotransferrin at the specific iron sites in the presence of bicarbonate. The apparent binding constants of these sites showed that the affinity of Yb3+ is lower than that of Fe3+and binding of Yb3+ in the N-lobe is kinetically favored while the C-lobe is thermodynamically favored. The first Yb3+ bound to the C-lobe quantitatively with a Yb/apotransferrin molar ratio of < 1, whereas the binding to the other site is weaker and approaches completeness by a higher molar ratio only. As demonstrated by 1H NMR spectra, Yb3+ binding disturbed the conformation of apotransferrin in a manner similar to Fe3+. Flow cytometric studies on the uptake of fluorescein isothiocyanate labeled Yb3+-bound transferrin species by K562 cells showed that they bind to the cell receptors. Laser scanning confocal microscopic studies with fluorescein isothiocyanate labeled Yb3+-bound transferrin and propidium iodide labeled DNA and RNA in cells indicated that the Yb3+ entered the cells. The Yb3+-transferrin complex inhibited the uptake of the fluorescein labeled ferric-saturated transferrin (Fe2-transferrin) complex into K562 cells. The results demonstrate that the complex of Yb3+-transferrin complex was recognized by the transferrin receptor and that the transferrin-receptor-mediated mechanism is a possible pathway for Yb3+ accumulation in cells.

Binding, Competitive↗
PubMed1999

Drosophila melanogaster transferrin. Cloning, deduced protein sequence, expression during the life cycle, gene localization and up-regulation on bacterial infection.

Drosophila melanogaster transferrin cDNA was cloned from an ovarian cDNA library by using a PCR fragment amplified by two primers designed from other dipteran transferrin sequences. The clone (2035 bp) encodes a protein of 641 amino acids containing a signal peptide of 29 amino acids. Like other insect transferrins, Drosophila transferrin appears to have a functional iron-binding site only in the N-terminal lobe. The C-terminal lobe lacks iron-binding residues found in other transferrins, and has large deletions which make it much smaller than functional C-terminal lobes in other transferrins. In-situ hybridization using a digoxigenin labeled transferrin cDNA probe revealed that the gene is located at position 17B1-2 on the X chromosome. Northern blot analysis showed that transferrin mRNA was present in the larval, pupal and adult stages, but was not detectable in the embryo. Iron supplementation of the diet resulted in lower levels of transferrin mRNA. When adult flies were inoculated with bacteria (Escherichia coli), transferrin mRNA synthesis was markedly increased relative to controls.

Amino Acid Sequence↗
PubMed2000

[Human amniotic fluid transferrin stimulates progesterone production by human trophoblast cells in vitro].

OBJECTIVE: During pregnancy transferrin plays a key role as an iron transport protein to serve the increased fetal demands of iron. Transferrin is also present in relatively high concentrations in amniotic fluid [6], showing a different glycosylation compared with serum transferrin. The biological function of human amniotic fluid transferrin (hAFT) is still unknown. In addition trophoblast cells also synthesise transferrin. Transferrin synthesised by the trophoblast shows a special glycosylation. We found identical carbohydrate structure of hAFT and trophoblast transferrin. We investigated the influence of hAFT on the progesterone-, cortisol- and hCG-release of trophoblasts in culture compared with the influence of human holo- and apo-serum transferrin on the release of these hormones. MATERIAL AND METHODS: Cytotrophoblast cells were prepared from human term placentae by standard trypsin-DNAse dispersion of villous tissue followed by a percoll gradient centrifugation step. When placed in culture, the trophoblasts were incubated with varying concentrations (50-300 micrograms/ml) of human amniotic fluid- and serum-transferrin. Unstimulated cells of each placenta used as controls. Culture supernatants were assayed for progesterone, hCG and cortisol by enzyme-immunometric methods. RESULTS: Our results show, that the release of progesterone increased in hAFT-treated cell cultures compared to untreated cell cultures. Holo- and apo-serumtransferrin did not show any effect on the progesterone release by trophoblast cells in vitro. Neither hAFT nor holo- and apo-serum transferrin had any effect on the cortisol- and hCG-release in vitro. CONCLUSIONS: Progesterone is a marker for differentiation of trophoblasts in syncytiotrophoblasts. Only hAFT stimulates the progesterone production. We suggest, that hAFT can modulate the endocrine function of trophoblast cells in culture by regulating progesterone production.

Amniotic Fluid↗
PubMed1996

Transcriptional suppression of the transferrin gene by hypolipidemic peroxisome proliferators.

Activation of gene expression by hypolipidemic peroxisome proliferators (e.g. native and substituted long chain fatty acids, aryloxyalkanoic fibrate drugs) is accompanied by transcriptional suppression of liver transferrin gene in treated animals or human hepatoma cell line. Transcriptional suppression of liver transferrin by hypolipidemic peroxisome proliferators results from (a) displacement of hepatic nuclear factor (HNF)-4 from the transferrin promoter by nonproductive binding of the peroxisome proliferator-activated receptor-retinoic acid X receptor heterodimer to the (-76/-52) PRI promoter element of the human transferrin gene and (b) suppression of liver HNF-4 gene expression by hypolipidemic peroxisome proliferators with a concomitant decrease in its availability for binding to the transferrin PRI promoter element. HNF-4 gene suppression and its displacement from the transferrin promoter result in eliminating HNF-4-enhanced transcription of transferrin. Liver transferrin suppression by hypolipidemic peroxisome proliferators may result in reduced iron availability as well as modulation of transferrin-induced differentiation processes. Transcriptional suppression of HNF-4-enhanced liver genes (e.g. apolipoprotein C-III, transferrin) may complement the pleiotropic biological effect exerted by hypolipidemic peroxisome proliferators.

Animals↗
PubMed1996

Serum transferrin and ferritin in pubertal boys: relations to body growth, pubertal stage, erythropoiesis, and iron deficiency.

We studied serum transferrin and ferritin concentrations in relation to individual body growth, stage of puberty, blood hemoglobin, and red blood cell iron (RBCI) in 60 prepubertal or early pubertal boys at 3-mo intervals for 18 mo. One-third of the boys had increased serum transferrin concentrations and almost all had decreased ferritin concentrations during the followup. No change in mean transferrin was observed but the individual 18-mo increments in transferrin correlated positively with the increments in hemoglobin (r = 0.55, P < 0.001) and in estimated RBCI (r = 0.31, P = 0.02). Serum transferrin remained stable at different genital stages, but ferritin was lower in the pubertal than in the prepubertal boys. Transferrin concentrations at 18 mo correlated positively with the preceding weight velocities. The rise in transferrin did not lead to an increase in iron-deficiency anemia. In contrast, transferrin rose in boys whose hemoglobin increased. In pubertal boys with relatively ample iron status, serum transferrin may be an indicator of increased availability of iron for erythropoiesis. The declining ferritin concentration indicates that part of the extra iron is mobilized through redistribution from stores to red blood cell mass and is generally associated with greatly increasing absorption. Thus, the pubertal changes in transferrin and ferritin are not necessarily indications of iron deficiency.

Anemia, Iron-Deficiency↗
PubMed2004

Oxidative stress induced by iron released from transferrin in low pH peritoneal dialysis solution.

BACKGROUND: Transferrin binds extracellular iron and protects tissues from iron-induced oxidative stress. The binding of iron and transferrin is pH dependent and conventional peritoneal dialysis (PD) solutions have unphysiologically low pH values. Herein, we investigated whether conventional PD solution releases iron from transferrin and if the released iron causes oxidative stress. METHODS: Effects of PD solutions on iron binding to transferrin were examined with purified human transferrin and transferrin in dialysates drained from PD patients. Oxidative stress induced by iron released from transferrin was evaluated in terms of the formation of thiobarbituric acid reactive substance (TBARS) and protein carbonylation in the human red blood cell (RBC) membrane. The iron deposition in peritoneal tissue from PD patients was evaluated by Perls' staining with diaminobenzidine intensification. RESULTS: Low pH PD solution released iron from transferrin. This iron release occurred within 1 min. Iron release was not observed in neutralized PD solution. Iron released from transferrin in low pH PD solution increased TBARS formation and protein carbonylation in the human RBC membrane. Iron deposition, which is prominent in the fibrotic area facing the peritoneal cavity, was observed in the peritoneum of PD patients. CONCLUSIONS: Iron released from transferrin in low pH PD solution can produce oxidative stress in the peritoneum of a PD patient. Neutralizing PD solution can avoid this problem. Iron deposition in the peritoneum may participate in the pathogenesis of peritoneal fibrosis in PD patients.

Dialysis Solutions↗
PubMed1996

Transcriptional regulation of sertoli cell differentiation by follicle-stimulating hormone at the level of the c-fos and transferrin promoters.

One of the primary endocrine hormones that influence the onset of Sertoli cell differentiation at puberty and help maintain differentiation in the adult testis is FSH. FSH can modulate the majority of Sertoli cell differentiated functions, including stimulation of the iron-binding protein transferrin. Previous studies have shown that FSH alters the levels of cAMP and the immediate early gene c-fos. The current study was designed to investigate the transcriptional regulation of Sertoli cell differentiation by examining the actions of FSH on the promoter of the immediate early gene c-fos and the promoter of the downstream differentiated function gene transferrin. The regulation of c-fos by FSH was investigated with various chloramphenicol acetyltransferase (CAT) constructs containing segments of the c-fos promoter, such as the serum response element (SRE), cAMP response element (CRE), and AP1/phorbol ester/TPA response element (TRE), that were transfected into cultured Sertoli cells. Observations indicate that FSH can stimulate all three response elements, as well as a whole c-fos promoter construct. Interestingly, FSH was found to have a more dramatic effect on the SRE-CAT than a cAMP analog, suggesting a difference in the actions of the two agents. Gel mobility shift assays were performed to confirm the reporter gene results. Nuclear extracts of FSH-stimulated Sertoli cells caused a labeled AP1 oligonucleotide to form a DNA/protein complex (i.e., gel shift), indicating activation of the c-fos gene and binding of the c-fos/jun complex. Nuclear extracts from both FSH- and cAMP-stimulated Sertoli cells promoted similar gel shifts with SRE and CRE oligonucleotides. This observation supports the reporter gene data in indicating that FSH can influence both the SRE and CRE. A gel mobility shift assay was also performed with an oligonucleotide containing the 5'-flanking ETS domain of the SRE (ETS-SRE) that allows the formation of a ternary complex. FSH-stimulated Sertoli cell nuclear extracts were found to promote a unique ETS-SRE gel shift not present in cAMP-stimulated cells. The observations imply that FSH actions on the SRE are in part distinct from the actions of cAMP. Transferrin gene expression was examined to study the downstream regulation of Sertoli cell differentiation. CAT constructs containing deletion mutants of a 3-kb mouse transferrin promoter were used. When transfected into Sertoli cells, the 581-bp transferrin minimal promoter, previously shown to contain a CRE, had a significant response to cAMP and FSH. The 1.6-, 2.6-, and 3-kg transferrin promoter constructs also responded to FSH and cAMP to the same extent as, or to a lesser extent than, the 581-bp minimal promoter. Interestingly, the actions of FSH on the 581-bp minimal transferrin promoter were more dramatic than those of cAMP. The importance of FSH-induced c-fos in the regulation of transferrin expression was demonstrated in the current study when a c-fos antisense oligonucleotide was found to partially inhibit (50%) the ability of FSH to induce the expression of a transferrin promoter (CAT) construct. Therefore, FSH appears to act through multiple transcriptional activation pathways. The first involves cAMP and the CRE at both early-event genes (e.g., c-fos) and downstream genes (e.g., transferrin). It is likely that other pathways involve alternate signal transduction events (e.g., calcium mobilization) and promoter response elements (e.g., SRE). These multiple pathways may act in a compensatory manner to assure the ability of FSH to influence Sertoli cell differentiation and/or in a synergistic manner to amplify FSH actions.

Animals↗
PubMed2001

Non-transferrin-bound iron in alcohol abusers.

BACKGROUND: Non-transferrin-bound iron, a low-molecular-weight iron complex capable of initiating free radical formation and lipid peroxidation, has been detected in the serum of animals experimentally fed with alcohol, but no data have been reported in alcohol abusers. The purpose of this study was to evaluate whether non-transferrin-bound iron is present in chronic alcohol abusers with liver involvement and whether alcohol plays any part in its appearance. METHODS: We measured non-transferrin-bound iron in a cohort of chronic alcohol abusers with and without liver cirrhosis at presentation, when 43 were active abusers and 33 were abstainers, and in a smaller group during a follow-up period. RESULTS: At presentation, non-transferrin-bound iron was detectable in 83.7% of active abusers but only in 21.2% of abstainers, and within the group of abusers, patients with cirrhosis had significantly higher non-transferrin-bound iron than patients without. Non-transferrin-bound iron was present not only in patients with transferrin saturation >45% but also in those with transferrin saturation < or =45%. Multiple regression analyses revealed that only alcohol intake and total bilirubin were associated independently with non-transferrin-bound iron values. Longitudinal study confirmed the data of the cross-sectional study. CONCLUSIONS: Non-transferrin-bound iron could have a role in initiating or promoting alcohol-induced liver damage.

Adult↗
PubMed1998

Anti-transferrin receptor monoclonal antibody: a novel immunosuppressant.

BACKGROUND: Transferrin receptor is a widely distributed cell surface receptor present on most proliferating and highly specialized quiescent cells. Expression of transferrin receptor on the surface of immune cells is up-regulated during T-cell activation after the interaction of the antigen-MHC with the T cell receptor. The role of transferrin receptor in T-cell activation has not been well-established. Since transferrin receptor is physically associated with the CD3 zeta-chain, blockade of transferrin receptor has the potential to interfere with the T-cell signals important in transplant rejection. METHODS: Anti-transferrin receptor monoclonal antibody (mAb) was administered in vivo and in vitro to determine whether this agent was effective in prolonging allograft survival and altering cell-mediated immunity. RESULTS: Using donor C57BL/6J (H2b) hearts transplanted to CBA/J (H2k) recipients, anti-transferrin receptor mAb at the time of transplantation prolonged cardiac allograft mean survival time to 25.7+/-0.9 days compared with untreated (13.3+/-0.6 days, P < 0.05) or isotype-matched (10.7+/-0.4 days, P < 0.05) controls. Anti-transferrin receptor mAb administered in vivo failed to suppress the subsequent allogeneic responses. However, when added to culture, anti-transferrin receptor mAb suppressed the allogeneic cytotoxic T lymphocyte response by 79-100% but not the mixed lymphocyte response. CONCLUSIONS: These studies are the first to suggest that transferrin receptor is a potential therapeutic target for clinical transplantation. Future studies will determine the most efficacious dose and time for maximal immunosuppression and the mechanisms responsible for the immunosuppression exhibited by antitransferrin receptor mAb.

Adjuvants, Immunologic↗
PubMed1997

Complex regulation of transferrin receptors during erythropoietin-induced differentiation of J2E erythroid cells--elevated transcription and mRNA stabilisation produce only a modest rise in protein content.

The regulation of transferrin-receptor synthesis was studied in J2E erythroid cells induced to differentiate with erythropoietin. Nuclear run-on assays demonstrated that transcription of the transferrin-receptor gene rose markedly after erythropoietin treatment. In addition, transferrin-receptor mRNA was stabilised and this was associated with an increase in the activity of the RNA-binding protein IRP (iron regulatory protein). As a result of increased transcription and mRNA stabilisation, steady-state RNA levels increased 10-20-fold. However, despite these large increases in mRNA, translation only doubled; consequently, modest increases in total protein and surface transferrin receptors were observed. Moreover, this rise in transferrin receptors was transient, and correlated with a burst of proliferation shortly after erythropoietin treatment. The expected inverse relationship between transferrin receptors and ferritin did not occur during J2E maturation as translation of both ferritin subunits increased when transferrin-receptor mRNA levels rose. Analysis of mutant J2E clones incapable of synthesising haemoglobin revealed that surface transferrin-receptor levels were only 15-25% that of the parental erythroid line. We propose that the surface expression of transferrin receptors in J2E cells is governed by three factors: basal levels essential for normal growth in culture; elevated levels needed for haemoglobin synthesis; and a transient erythropoietin-induced increase that is required for the final burst of proliferation. It was concluded that the regulation of transferrin-receptor production in erythropoietin-stimulated J2E cells is complex and that there are several sites of control.

Animals↗
PubMed2004

Transferrin saturation with intravenous irons: an in vitro study.

BACKGROUND: Iron deficiency anemia in chronic kidney disease is commonly treated with one of three intravenous irons-iron dextran, iron sucrose, or iron gluconate. Substantial pharmacologic differences between drugs exist, but their ability to saturate transferrin has not been compared. Drugs that may lead to rapid transferrin saturation may lead to greater efficacy but also increased toxicity if transferring-mediated uptake of iron is the basis of this toxicity. METHODS: We studied the in vitro ability of the three intravenous irons to donate iron to transferrin. Transferrin saturation was studied by direct visualization of the transferrin bands by urea polyacrylamide gel electrophoresis (PAGE), as well as a functional assay that evaluated the ability of iron to half saturate transferrin in a dose-dependent (0 to 100 microg/mL) and time-dependent (15 to 180 min) manner. Half-maximal dose (EC(50)) of iron needed to saturate transferrin was evaluated. RESULTS: Nondextran irons were able to saturate transferrin in a dose-dependent and time-dependent manner. There was more rapid transferrin saturation with iron gluconate compared to iron sucrose. The slope of the EC(50) versus dose iron gluconate titration curve was -0.021 nmol/microg/mL (95% CI -0.025 to -0.017, P < 0.0001), for iron sucrose -0.006 nmol/microg/mL (95% CI -0.010 to -0.002, P= 0.002), and for iron dextran -0.001 nmol/microg/mL (95% CI -0.004 to 0.003, P > 0.2). The least square mean EC(50) computed for mean iron concentration was 5.95 nmol for iron gluconate (95% CI 5.82 to 6.08), 6.73 nmol for iron sucrose (95% CI 6.59 to 6.86), and 7.24 nmol for iron dextran (95% CI 7.11 to 7.38). Similar results were seen for the time-dependent transferrin saturation (drug x time interaction, F 6.0, P < 0.01). Urea PAGE analysis showed similar results as the functional assay. CONCLUSION: Substantial heterogeneity in direct iron transfer from iron pharmaceuticals in vitro suggests that differences may exist in safety and efficacy of these drugs in vivo. In vivo studies are needed to compare the safety and efficacy of existing nondextran parenteral irons to better define the therapeutic ratio.

Ferric Compounds↗
PubMed1988

Possible mechanism of ineffective erythropoiesis by an altered transferrin receptor cycle in erythroleukemia.

Involvement of the transferrin receptor cycle was noted in erythroblasts from a patient with erythroleukemia (FAB classification M6). The kinetics of transferrin receptor cycle in bone marrow erythroblasts was obtained by pulse-chase experiments before the initiation of therapy. Internalization of transferrin was impaired and resulted in a delayed peak of internalized transferrin, as compared with the kinetics pattern seen in healthy subjects. The subsequent exocytosis of the internalized ligand was also delayed. Thus, transferrin receptor cycle seems to be influenced all along the transferrin pathway, hence transferrin travels more slowly in erythroblasts in erythroleukemia. The altered transferrin receptor cycle led to a diminished iron uptake per surface transferrin receptor (approximately 30% of that in healthy subjects), and the incorporation of iron into heme was greatly reduced. Our observations suggest a possible role for the altered transferrin receptor cycle in the pathogenesis of defective heme synthesis and ineffective erythropoiesis in erythroleukemia.

Endocytosis↗
PubMed1983

Turnover in the transferrin iron pool during the hypoferremic phase of experimental Neisseria meningitidis infection in mice.

Mouse transferrin was used to specifically label the plasma transferrin iron pool for studies of iron kinetics in normal mice and infected mice during the hypoferremic phase of experimental meningococcal infection. The plasma transferrin iron pool of normal mice was found to be very dynamic, with a half-life of iron in the pool of 0.7 h. Iron left the plasma pool, entered the bone marrow, and was released into the blood in erythrocytes. Iron from the transferrin pool also entered the liver and spleen and was presumably in the reticuloendothelial system components of these organs. Most of the iron that had been supplied as transferrin iron was found in erythrocytes by 48 h after injection. Studies with mice infected with Neisseria meningitidis strain M1011 revealed similar kinetics for transferrin iron. There was no redistribution of iron within the various iron pools as a result of infection. Iron turnover in the plasma transferrin pool during the hypoferremic phase was similar to control rates, and iron leaving the pool entered its normal erythroid compartments. The lack of accelerated turnover of plasma iron and the finding that plasma iron was not rerouted to storage compartments during the hypoferremic phase provided good evidence that lactoferrin and leukocytic endogenous mediator were not directly involved in redirecting transferrin iron. Our evidence has implicated an impaired return of reticuloendothelial system-processed iron to the transferrin pool during the hypoferremic response. This appears to be a logical point in the erythroid iron cycle for host-mediated iron sequestration, as the reticuloendothelial system is involved in iron storage and may regulate iron levels in the plasma transferrin pool under normal conditions.

Animals↗
PubMed2004

Cleavage of human transferrin by Porphyromonas gingivalis gingipains promotes growth and formation of hydroxyl radicals.

Porphyromonas gingivalis, a gram-negative anaerobic bacterium associated with active lesions of chronic periodontitis, produces several proteinases which are presumably involved in host colonization, perturbation of the immune system, and tissue destruction. The aims of this study were to investigate the degradation of human transferrin by gingipain cysteine proteinases of P. gingivalis and to demonstrate the production of toxic hydroxyl radicals (HO*) catalyzed by the iron-containing transferrin fragments generated or by release of iron itself. Analysis by polyacrylamide gel electrophoresis and Western immunoblotting showed that preparations of Arg- and Lys-gingipains of P. gingivalis cleave transferrin (iron-free and iron-saturated forms) into fragments of various sizes. Interestingly, gingival crevicular fluid samples from diseased periodontal sites but not samples from healthy periodontal sites contained fragments of transferrin. By using (55)Fe-transferrin, it was found that degradation by P. gingivalis gingipains resulted in the production of free iron, as well as iron bound to lower-molecular-mass fragments. Subsequent to the degradation of transferrin, bacterial cells assimilated intracellularly the radiolabeled iron. Growth of P. gingivalis ATCC 33277, but not growth of an Arg-gingipain- and Lys-gingipain-deficient mutant, was possible in a chemically defined medium containing 30% iron-saturated transferrin as the only source of iron and peptides, suggesting that gingipains play a critical role in the acquisition of essential growth nutrients. Finally, the transferrin degradation products generated by Arg-gingipains A and B were capable of catalyzing the formation of HO*, as determined by a hypoxanthine/xanthine oxidase system and spin trapping-electron paramagnetic resonance spectrometry. Our study indicates that P. gingivalis gingipains degrade human transferrin, providing sources of iron and peptides. The iron-containing transferrin fragments or the release of iron itself may contribute to tissue destruction by catalyzing the formation of toxic HO*.

Adhesins, Bacterial↗
PubMed1995

Changes in transferrin saturation after treatment with the oral iron chelator deferiprone in patients with iron overload.

AIMS: To evaluate the changes in transferrin saturation in patients with iron overload following the oral administration of the iron chelator deferiprone; to assess the correlation between the degree of transferrin desaturation, the deferiprone dose, and urinary iron excretion. METHODS: Serum samples were obtained from 16 patients with iron overload at different time intervals following the oral administration of deferiprone (50 mg/kg). These samples were analysed using 6M urea/polyacrylamide gel electrophoresis (UPAGE). This method is able to resolve serum transferrin into four different forms (free iron, two forms of monoferric, and diferric). The deferiprone concentration in these samples was estimated using high pressure liquid chromatography (HPLC). Zero time samples (t0) from 10 patients were incubated with 150 microM deferiprone or normal saline either at room temperature or at 37 degrees C for 30 minutes and 24 hours, and also at -20 degrees C for six weeks. Samples were then analysed using UPAGE. RESULTS: A maximum decrease in transferrin saturation from (mean (SD)) 93.0 (10.6)% to 54.5 (17.2)% was observed 72.5 (50.0) minutes after deferiprone administration and in most of the patients coincided with peak deferiprone concentration. This was associated with a maximum rise in the percentage of iron free transferrin (apotransferrin) from 2.9 (7.0)% to 27.3 (17.8)%. The total amount of iron estimated to be removed from transferrin constituted 21.3 (20.2)% of the 24 hour urinary iron excretion measured during the study. When deferiprone (150 mumol/l) was incubated in vitro with t0 samples from 10 patients for 30 minutes and 24 hours at room temperature, 37 degrees C, and at -20 degrees C for six weeks, deferiprone was more efficient at removing iron from transferrin at 37 degrees C, with maximum transferrin desaturation accomplished within 30 minutes compared with 24 hours at room temperature. CONCLUSIONS: The results confirm that deferiprone can remove iron from transferrin when administered orally to patients with iron overload and that transferrin bound iron may, therefore, be a significant source of the iron chelated by deferiprone in vivo.

Administration, Oral↗
PubMed1987

The chromatographic heterogeneity of rat transferrin on immobilized concanavalin A and lentil lectin.

A procedure was developed for the isolation of the microheterogeneous forms of rat transferrin consisting of anion-exchange and serial lectin affinity chromatographies. By deploying this technique, four to five different anionic species of the protein were detected in plasma. The two major components obtained, which encompassed 92-94% of the plasma transferrin, were further studied by sequential lectin chromatography. The larger of the two, representing 60-63% of plasma transferrin, was bound by concanavalin A - Sepharose, while the smaller one (30-32% of plasma transferrin) resolved into an unbound (25-27% of plasma transferrin) and a retarded (4-5% of plasma transferrin) fraction. The latter eluted from the column in a volume which was 1.9 times larger than that required for the passage of nonretarded transferrin. In accordance with their fucose contents, each of these three concanavalin A fractions resolved into a bound (20-29%) and an unbound (71-80%) subfraction by chromatography on lentil-Sepharose. It is concluded that there exist two kinds of glycan microheterogeneity in rat transferrin and that they are unrelated to each other. Consequently, at least six different forms of rat transferrin are available with respect to glycosylation. Epididymal fucosidase cleaved fucose from apotransferrin slowly and from the tryptic glycopeptide rapidly. Exploratory studies performed in vivo failed thus far to identify the significance of fucose in rat transferrin.

Animals↗