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PubMed1996

Intestinal epithelia (Caco-2) cells acquire iron through the basolateral endocytosis of transferrin.

Although the absorption of iron through the intestinal epithelia is inversely related to body iron stores, the mechanisms by which the enterocytes sense body iron stores are unknown. Polarized enterocytes have transferrin receptors in their basolateral surface; hence, we tested the hypothesis that the endocytosis of circulating transferrin may be part of the body's iron sensing mechanism. Particularly, we evaluated the contribution of basolateral transferrin to iron content of intestinal cells, and we investigated what factors modulate this contribution. For this purpose, we used the intestinal cell line Caco-2 grown on porous filters. When the cells were simultaneously offered equimolar amounts of iron, from the apical medium as 55Fe-nitrilotriacetate and from the basolateral medium as 59Fe-transferrin, most of the internalized iron came from the basolateral endocytosis of 59Fe-transferrin. Experiments of transferrin binding and internalization showed that holotransferrin and apotransferrin had similar numbers of basolateral receptors. The receptors had associated constants for diferric transferrin, monoferric transferrin, and apotransferrin of 2.69, 1.71 and 0.26 x 10(7) L/mol, respectively. The binding of diferric transferrin or monoferric transferrin to receptors was competitively inhibited by apotransferrin. Caco-2 cells, but not K562 cells, showed inhibition of basolateral, transferrin-mediated iron uptake by apotransferrin. This inhibition should regulate the net basolateral uptake of iron mediated by the endocytosis of Fe-containing transferrins. We propose that the basolateral endocytosis of transferrin forms part of the system by which intestinal epithelia cells sense plasma iron concentrations.

Absorption↗

PubMed1988

Kinetics of transferrin endocytosis and iron uptake by intact isolated rat seminiferous tubules and Sertoli cells in culture.

The receptor-mediated endocytotic cycle of rat and human transferrin has been studied in intact, isolated rat seminiferous tubules and Sertoli cells in culture. Double-labeled [( 59Fe125I]) transferrin has been used to study the fate of transferrin and iron. Diferric transferrin binds to the tubules and the cultured Sertoli cells and is internalized. The iron remains inside, while the transferrin recycles and is released into the medium. Although, as reported before (Wauben-Penris et al., 1986), "extra" binding sites for human transferrin exist as compared to rat transferrin, this does not result in extra uptake of transferrin or iron. Both rat and human transferrin transport iron into the cells and recycle back to the surface, and do so with identical kinetics. A striking difference has been found between the mean efficient recycling times of the transferrin receptors in intact tubules (90 min) and in Sertoli cells in culture (21 min). Possible explanations of this difference are discussed. Light-microscopic autoradiography of [125 I]-labeled transferrin has revealed that the transferrin protein is excluded from the adluminal compartment, even after 21 h of incubation. This indicates that externally added transferrin itself does not deliver iron to the postmeiotic germ cells in intact, isolated rat seminiferous tubules.

Animals↗

PubMed1999

Iron-dependent regulation of transferrin receptor expression in Trypanosoma brucei.

Transferrin is an essential growth factor for African trypanosomes. Here we show that expression of the trypanosomal transferrin receptor, which bears no structural similarity with mammalian transferrin receptors, is regulated by iron availability. Iron depletion of bloodstream forms of Trypanosoma brucei with the iron chelator deferoxamine resulted in a 3-fold up-regulation of the transferrin receptor and a 3-fold increase of the transferrin uptake rate. The abundance of expression site associated gene product 6 (ESAG6) mRNA, which encodes one of the two subunits of the trypanosome transferrin receptor, is regulated 5-fold by a post-transcriptional mechanism. In mammalian cells the stability of transferrin receptor mRNA is controlled by iron regulatory proteins (IRPs) binding to iron-responsive elements (IREs) in the 3'-untranslated region (UTR). Therefore, the role of a T. brucei cytoplasmic aconitase (TbACO) that is highly related to mammalian IRP-1 was investigated. Iron regulation of the transferrin receptor was found to be unaffected in Deltaaco::NEO/Deltaaco::HYG null mutants generated by targeted disruption of the TbACO gene. Thus, the mechanism of post-transcriptional transferrin receptor regulation in trypanosomes appears to be distinct from the IRE/IRP paradigm. The transferrin uptake rate was also increased when trypanosomes were transferred from medium supplemented with foetal bovine serum to medium supplemented with sera from other vertebrates. Due to varying binding affinities of the trypanosomal transferrin receptor for transferrins of different species, serum change can result in iron starvation. Thus, regulation of transferrin receptor expression may be a fast compensatory mechanism upon transmission of the parasite to a new host species.

Aconitate Hydratase↗

PubMed1992

Iron and transferrin uptake by brain and cerebrospinal fluid in the rat.

Iron and transferrin uptake into the brain, CSF and choroid plexus, and albumin uptake into the CSF and choroid plexus, were determined after the intravenous injection of [59Fe-125I]transferrin and [131I]albumin into control rats aged 15, 21 and 63 days and 21-day iron-deficient rats. Iron uptake by the brain was unidirectional, greatly exceeded that of transferrin and was equivalent to 39 and 36% of the plasma iron pool per day in the 15-day control and 21-day iron-deficient rats. The rate of transferrin catabolism in the rats was only about 20% of the plasma pool per day. Iron and transferrin uptake into the brain and CSF decreased with increasing age and was greater in the iron-deficient than in the control 21-day rats. The quantity of 125I-transferrin recovered in the CSF could account for only a small proportion of the iron taken up by the brain. Albumin transfer to the CSF also decreased with age but was lower than that of transferrin and was not affected by iron deficiency. Similarly, the plasma: CSF concentration ratios of transferrin and albumin, as determined immunologically, decreased with age and were greater for transferrin than albumin. It is concluded that iron uptake by the brain is dependent on iron release from transferrin at the cerebral capillary endothelial cells with recycling of transferrin to the plasma and transfer of the iron into the brain interstitium. Only a small fraction of the transferrin bound by brain capillaries is transcytosed into the brain and CSF, this being one source of CSF transferrin while other sources are local synthesis and transfer from the plasma by the choroid plexuses.

Animals↗

PubMed1990

The biology of transferrin.

The chemistry and molecular biology of transferrin is discussed. The discussion covers the genetic control of transferrin synthesis, its intracellular synthesis, intra- and extracellular transport, and its interaction with transferrin receptors. The role of transferrin in iron metabolism is evaluated, both with regard to iron uptake by transferrin as to iron uptake from transferrin by different cells. The knowledge on the biochemical mechanisms involved in iron uptake is presented, with special reference to the triple role of the acidification of endocytotic vesicles. Apart from its traditional role in iron metabolism, transferrin acts as a growth factor. A distinction of two groups of growth-stimulating properties of transferrin has been made. As an early effect, membranous and intracellular changes are initiated, possibly based on electrochemical effects on the cell. The late effects seem to relate to its role in iron transport. Interestingly, the early growth stimulating effects can be segregated from the former function of transferrin and strictly speaking neither depend on iron nor on the transferrin molecule itself. Also the trophic effect of transferrin on several cell types has been described. Hypotheses concerning the biochemical basis of this effect are presented and within this context a new hypothesis on the differential occupation of iron binding sites of serum transferrin is forwarded. Examples of the applicability of present understanding of the biology of transferrin in clinical settings are presented.

Carbohydrate Sequence↗

PubMed1988

Nonidentical distribution of transferrin and ferric iron in human brain.

Using the avidin-biotin immunoperoxidase technique and a diaminobenzidine intensification of the Prussian Blue method, we have compared the distribution of transferrin to that of ferric iron in five normal autopsy brains from adult human males. The observed distribution of transferrin was considerably more widespread than: (1) that of histochemically demonstrable ferric iron; (2) that reported for transferrin in the fetal and neonatal human brain; and (3) that reported for transferrin in other species. Transferrin immunoreactivity was present in neurons, oligodendrocytes, astrocytes, ependymal cells, and choroid plexus epithelial cells, although not in all cells of any type. Ferric iron, on the other hand, was demonstrable only in oligodendrocytes, in myelin sheaths, and possibly in axons. While staining for both transferrin and iron was relatively high in the basal ganglia and substantia nigra, the pattern of staining differed, with striatal efferent fibers staining more heavily than the neuropil for iron and less heavily than the neuropil for transferrin. The choroid plexus, which in the rat has been shown to synthesize transferrin, stained heavily for transferrin and not at all for iron. The findings of low iron and high transferrin in the choroid plexus suggest that the plexus may secrete transferrin into the cerebrospinal fluid, thereby facilitating the translocation of iron within the neuraxis. Furthermore, the nonidentical distribution of ferric iron and transferrin suggests that, in the human brain, transferrin may serve other functions besides the transport of iron from extracellular fluid to cytoplasm.

Adult↗

PubMed1998

Distribution of transferrin saturation in an Australian population: relevance to the early diagnosis of hemochromatosis.

BACKGROUND & AIMS: An elevated transferrin saturation is the earliest phenotypic abnormality in hereditary hemochromatosis. Determination of transferrin saturation remains the most useful noninvasive screening test for affected individuals, but there is debate as to the appropriate screening level. The aims of this study were to estimate the mean transferrin saturation in hemochromatosis heterozygotes and normal individuals and to evaluate potential transferrin saturation screening levels. METHODS: Statistical mixture modeling was applied to data from a survey of asymptomatic Australians to estimate the mean transferrin saturation in hemochromatosis heterozygotes and normal individuals. To evaluate potential transferrin saturation screening levels, modeling results were compared with data from identified hemochromatosis heterozygotes and homozygotes. RESULTS: After removal of hemochromatosis homozygotes, two populations of transferrin saturation were identified in asymptomatic Australians (P < 0.01). In men, 88.2% of the truncated sample had a lower mean transferrin saturation of 24.1%, whereas 11.8% had an increased mean transferrin saturation of 37.3%. Similar results were found in women. A transferrin saturation threshold of 45% identified 98% of homozygotes without misidentifying any normal individuals. CONCLUSIONS: The results confirm that hemochromatosis heterozygotes form a distinct transferrin saturation subpopulation and support the use of transferrin saturation as an inexpensive screening test for hemochromatosis. In practice, a fasting transferrin saturation of > or = 45% identifies virtually all affected homozygous subjects without necessitating further investigation of unaffected normal individuals.

Adult↗

PubMed2001

Products of proteolytic cleavage of transferrin induce nitric oxide response of goldfish macrophages.

Enzymatic cleavage product of transferrin induced the production of nitric oxide (NO) by LPS-stimulated goldfish macrophages. A NO-inducing factor was purified from the supernatants of mitogen-stimulated goldfish kidney leukocytes using fast performance liquid chromatography (FPLC) and the purified proteins analyzed by microcapillary reverse-phase HPLC nano-electrospray tandem mass spectrometry. The proteins were identified as truncated forms of transferrin, having approximate molecular weights (MW) of 33, 35, and 37kDa (kilodaltons). The precursor form (i.e. full-length) of transferrin did not enhance NO production by LPS-stimulated goldfish macrophages, but enzymatic cleavage of this precursor form correlated with enhanced production of NO by goldfish macrophages. Enzymatic cleavage of transferrin was dependent on the presence of stimulated kidney leukocytes and was shown to occur in response to both mixed lymphocyte reactions (MLR) and the mitogenic stimulation of goldfish kidney leukocytes. Time course analysis revealed that 24h after kidney leukocyte MLR or mitogen stimulation, cleaved transferrin products appeared in the supernatants of cultured cells, which was related to the on-set of NO-inducing activity of these preparations. To confirm these findings, bovine transferrin was digested in vitro using protease XXVII. The resulting cleavage products had approximate MW of 33, 35, and 37kDa. When these peptides were subjected to the purification protocols used to purify a NO-inducing factor from goldfish leukocyte supernatants, they were shown to elute to identical fractions. To examine the potential role of fish transferrin in mediating goldfish NO production, carp transferrin was purified from serum and following protease-digestion and purification by FPLC, the truncated proteins were found to elute to similar fractions as bovine transferrin. Furthermore, mitogen-stimulated leukocyte supernatants prepared in the absence of bovine serum (carp serum only) retained NO-inducing activity, indicating that this response was not an artifact of bovine serum components (i.e. bovine transferrin). Anti-bovine and anti-carp transferrin polyclonal antibodies identified the presence of truncated forms of transferrin in the active fractions of FPLC-separated mitogen-stimulated leukocyte supernatants prepared in the presence of bovine or carp serum, respectively. Thus, our results suggest a novel role for fish transferrin as one of the factors that mediates teleost macrophage antimicrobial functions.

Animals↗

PubMed1997

Carbohydrate deficient transferrin (CDT) in alcoholic cirrhosis: a kinetic study.

BACKGROUND/AIMS: Carbohydrate deficient transferrin has been introduced as a marker of excessive alcohol intake. The present study was undertaken in order to measure the circulating level of carbohydrate deficient transferrin in patients with alcoholic cirrhosis and to assess arteriovenous kinetics of carbohydrate deficient transferrin in liver and kidney. METHODS/RESULTS: The median value of serum carbohydrate deficient transferrin was 16.0 U/l in patients with alcoholic cirrhosis (n = 41), and this value was not significantly different from that of a normal control group (median 17.4 U/l, n = 55, ns). Carbohydrate deficient transferrin was significantly higher in patients with cirrhosis and high current alcohol intake than in abstaining patients (20 vs. 14 U/l, p < 0.05). Similarly, controls with a high current alcohol intake (> 50 g/day) had a significantly higher carbohydrate deficient transferrin concentration than controls with a low alcohol intake (< 10 g/day) (36 vs. 14.9 U/l, p < 0.005). No significant differences were detected between carbohydrate deficient transferrin in artery and liver vein or artery and renal vein, either in patients with alcoholic cirrhosis (n = 11) or in controls (n = 8), which indicates a slow turnover rate of carbohydrate deficient transferrin. Food ingestion did not affect the circulating level of carbohydrate deficient transferrin, and the analysis of carbohydrate deficient transferrin was almost unaffected by the presence of ethanol in plasma within the biological range (ethanol 0-100 mmol/l). CONCLUSIONS: Our results suggest that measurement of carbohydrate deficient transferrin may be used in patients with alcoholic cirrhosis. High current alcohol intake is associated with higher carbohydrate deficient transferrin levels than in those with low alcohol intake, but the overlap is substantial in patients with cirrhosis. Carbohydrate deficient transferrin has a low turnover rate in both patients with cirrhosis and normals.

Adult↗

PubMed1984

Purification and characterization of testicular transferrin secreted by rat Sertoli cells.

Sertoli cells synthesize and secrete a transferrin-like protein (testicular transferrin) [Skinner & Griswold (1980) J. Biol. Chem. 255, 1923-1925]. The purpose of the present study was to purify and characterize testicular transferrin and to compare it with serum transferrin. Testicular transferrin was obtained from the medium of cultured rat Sertoli cells, whereas serum transferrin was obtained from rat serum. Both proteins were purified with the use of phenyl-Sepharose hydrophobic chromatography and transferrin immunoaffinity chromatography. The purified proteins were shown to have similar molecular masses (75 000 Da) and amino acid compositions. The pattern of tryptic peptides from testicular and serum transferrin were found to be essentially the same when analysed by reverse-phase high-pressure liquid chromatography. The carbohydrate composition of both transferrins was determined by several colorimetric assays and g.l.c. Testicular transferrin, isolated from cell culture medium, had increased amounts of glucose, galactose and glucosamine. Serum transferrin that was incubated with cell culture medium also had a large amount of associated glucose. The results show that testicular transferrin and serum transferrin are structurally very similar and are possibly products of the same gene expressed in two different tissues, the testis and liver. However, the amount of carbohydrate associated with these two proteins is different.

Amino Acids↗

PubMed1997

Transferrin promotes endothelial cell migration and invasion: implication in cartilage neovascularization.

During endochondral bone formation, avascular cartilage differentiates to hypertrophic cartilage that then undergoes erosion and vascularization leading to bone deposition. Resting cartilage produces inhibitors of angiogenesis, shifting to production of angiogenic stimulators in hypertrophic cartilage. A major protein synthesized by hypertrophic cartilage both in vivo and in vitro is transferrin. Here we show that transferrin is a major angiogenic molecule released by hypertrophic cartilage. Endothelial cell migration and invasion is stimulated by transferrins from a number of different sources, including hypertrophic cartilage. Checkerboard analysis demonstrates that transferrin is a chemotactic and chemokinetic molecule. Chondrocyte-conditioned media show similar properties. Polyclonal anti-transferrin antibodies completely block endothelial cell migration and invasion induced by purified transferrin and inhibit the activity produced by hypertrophic chondrocytes by 50-70% as compared with controls. Function-blocking mAbs directed against the transferrin receptor similarly reduce the endothelial migratory response. Chondrocytes differentiating in the presence of serum produce transferrin, whereas those that differentiate in the absence of serum do not. Conditioned media from differentiated chondrocytes not producing transferrin have only 30% of the endothelial cell migratory activity of parallel cultures that synthesize transferrin. The angiogenic activity of transferrins was confirmed by in vivo assays on chicken egg chorioallantoic membrane, showing promotion of neovascularization by transferrins purified from different sources including conditioned culture medium. Based on the above results, we suggest that transferrin is a major angiogenic molecule produced by hypertrophic chondrocytes during endochondral bone formation.

Allantois↗

PubMed1984

Transferrin and iron uptake by rat hepatocytes in culture.

Hepatic iron and transferrin metabolism was studied using rat transferrin doubly labeled with 59Fe and 125I and adult rat hepatocytes in primary monolayer culture. Iron uptake was linear for 48 h while transferrin uptake was biphasic. Total transferrin and iron uptake increased in a linear manner as the transferrin concentration was raised up to at least 130 microM. This indicates that transferrin and iron are taken up primarily by nonspecific processes, possibly by endocytosis (absorptive or fluid) and by the action of iron chelators. However, some evidence indicated the presence of receptors for diferric transferrin on hepatocytes: the molar ratio of iron to transferrin accumulation increased with incubation time, transferrin and iron uptake was proportional to the iron saturation of the transferrin, apotransferrin displaced bound apotransferrin but had no effect on the binding of diferric transferrin, and the molar ratio of iron to transferrin uptake decreased with increasing transferrin concentrations.

Animals↗

PubMed1995

Transferrin concentrations in serum and lower respiratory tract fluid of mechanically ventilated patients with COPD or ARDS.

Transferrin serves as the primary iron transport protein in serum, but it also is present in the lower respiratory tract where it has antioxidant and antibacterial properties. Prior studies indicate that patients with respiratory failure (RF) due to ARDS have increased concentrations of transferrin in the lower respiratory tract, which is attributed to increased lung vascular permeability. It is unclear whether mechanical ventilation contributes to increased lung transferrin content in patients with ARDS, although mechanical ventilation may increase lung microvascular permeability. To assess whether mechanical ventilation in patients with RF due to causes other than ARDS is also associated with increased respiratory tract concentrations of transferrin, we compared transferrin concentrations in serum and lung lavage fluid obtained from 12 mechanically ventilated patients with RF attributable to COPD, 6 patients with ARDS, and 15 healthy volunteers. Serum transferrin concentrations in patients with RF due to COPD were variable, but mean concentrations were similar to those in control subjects (336 +/- 58 vs 307 +/- 9 [SE] mg/dL), whereas serum transferrin concentrations were decreased in patients with ARDS (182 +/- 68 mg/dL; p < 0.05). Compared with control subjects, lavage fluid recovered from patients with RF due to COPD contained significantly decreased concentrations of transferrin (1.56 +/- 0.24 vs 4.27 +/- 0.44 micrograms/mL; p < 0.001), whereas transferrin concentrations in lavage fluid recovered from patients with ARDS were increased (15.72 +/- 2.01 micrograms/mL; p < 0.001). Transferrin concentrations of lavage fluid also were decreased in COPD patients when normalized for lavage fluid protein content (4.35 +/- 0.72 vs 19.96 +/- 3.13 micrograms/mg in control subjects, p < 0.001). These data indicate that mechanical ventilation of patients with COPD is associated with decreased lung transferrin concentrations, in contrast to an increased transferrin concentration found in patients with ARDS. Decreased transferrin concentrations in the lower respiratory tract may decrease defenses against oxidant injury and bacterial infection in patients with RF due to COPD.

Adult↗

PubMed1992

Purification of ovine transferrin and study of the hormonal control of its secretion in enriched cultures of ovine Sertoli cells.

Ovine transferrin (o-transferrin) was purified from sheep serum by fractionated precipitation with ammonium sulphate, ion-exchange chromatography on DEAE trisacryl and finally by affinity chromatography on Affigel blue to remove albumin. Ovine transferrin was identified by its apparent molecular weight in sodium dodecyl sulphate polyacrylamide gel electrophoresis and by its N-terminal amino-acid sequence. The procedure presented in this report permits the preparation of highly purified o-transferrin with a good recovery (52% of initial total immunoactivity). An antiserum against o-transferrin was then raised in rabbits, using this highly purified preparation. A specific radioimmunoassay was set up using 125I-labelled o-transferrin. Its detection threshold (4 ng/ml) was low enough to measure o-transferrin in spent culture media of ovine Sertoli cells, which ranged between 15 and 600 ng/ml. Sheep seminiferous tubule cells, containing approximately 80% Sertoli cells, were cultured at a high density (1.5 x 10(6) cells/cm2) on a thin layer of reconstituted basement membrane. Kinetic studies showed that basal daily secretion of o-transferrin was reduced by half (-49%) between Day 1 and Day 2 of culture, and progressively decreased thereafter. Under FIRT (500 ng ovine follicle-stimulating hormone (FSH)/ml + 10 micrograms insulin/ml + 500 ng retinol/ml + 5 x 10(-7) mol/l testosterone) stimulation, the ratio of stimulated to basal secretions increased 11-fold between Day 1 (1.1) and Day 6 (12). When 10% fetal calf serum was added, mean o-transferrin secretion was a third of that in serum-free medium, suggesting that fetal calf serum contains factors that inhibit secretion of ovine Sertoli cell transferrin. In the presence of serum, the ratio of FIRT-stimulated to basal secretions doubled between Day 1 (1.0) and Day 4-6 (2.0). Between Days 2 and 4 of culture, insulin had a slight stimulatory effect on o-transferrin secretion (128% of control at 10 micrograms insulin/ml), as well as epidermal growth factor (124% of control at 50 ng/ml). Testosterone at up to 5 x 10(-7) mol/l had no effect; 500 ng retinol/ml doubled o-transferrin secretion (218% of control) as did 500 ng FSH/ml (220% of control). A combination of retinol and FSH increased the secretion 4-fold, indicating that maximal stimulation of o-transferrin secretion by ovine Sertoli cells requires the combined actions of mechanisms dependent and independent of cAMP.

Animals↗

PubMed1997

Investigation of the potential role of the germ cell complement in control of the expression of transferrin mRNA in the prepubertal and adult rat testis.

Iron is required for the normal development of germ cells during spermatogenesis. Because these cells have no direct access to systemic iron, there exists a shuttle system involving production and secretion of the iron-transporting protein transferrin by the Sertoli cells. Previous reports using cultures of immature Sertoli cells exposed to adult germ cells, or in vivo studies involving germ cell depleted adult rat testes, concluded that production of transferrin by Sertoli cells is modulated by germ cell complement. In the present study we have used in situ hybridisation with cRNA probes directed against the 5' and 3' ends of transferrin mRNA to examine the pattern of expression of transferrin in the immature and adult rat testis. Adult rats were treated with ethane dimethane sulphonate or methoxyacetic acid (MAA) to manipulate their testosterone levels or germ cell complement respectively. Initial findings obtained using the 3' probe showed a decrease in transferrin mRNA associated with round spermatid depletion. However, these data were not confirmed by in situ hybridisation when the 5' probe was used. The specificity of the probes was examined using Northern blotting and the 3' probe was found to hybridise to the germ cell transcript for hemiferrin even under conditions of high stringency. Examination of immature and pubertal rat testes by in situ hybridisation using the 5' transferrin-specific probe found that as early as 14 days of age the level of expression of transferrin mRNA was clearly different between tubules, and the mRNA appeared to be expressed in Leydig cells on and after day 31. In the adult rat testis, maximal expression of transferrin mRNA was found at stages VIII-XIV, calling into question the interpretation of the results of some previous studies showing expression of transferrin mRNA at all stages of the spermatogenic cycle. This stage-specific pattern of expression was not altered by acute germ cell depletion using MAA. However, Northern blot analysis showed a statistically significant increase in transferrin mRNA expression at 7 days after MAA treatment when pachytene spermatocytes were depleted from tubules at all stages of the spermatogenic cycle at which transferrin is normally expressed. In conclusion, we found that transferrin mRNA expression was not modulated by round spermatids as has been reported previously but that meiotic germ cells may influence expression of transferrin at specific stages of the spermatogenic cycle.

Animals↗

PubMed2006

[Concentrations of serum iron and transferrin in children with nephrotic syndrome].

OBJECTIVE: Nephrotic syndrome (NS) is characterized by marked urinary excretion of albumin and other intermediated-size plasma proteins such as transferrin. The aim of this study was to determine the changes of serum iron and transferrin and the relationship between the serum and urinary transferrin. METHODS: The indexes related to iron metabolism, including serum iron, ferritin, transferrin, total iron-binding capacity, transferrin saturation and hematological parameters (Hb, MCV, MCH), and urinary transferrin were measured in 37 children with NS before treatment and at the remission stage. Thirty-five age-matched healthy children served as controls. RESULTS: Serum iron levels (18.8 +/- 3.8 micromol/L) in NS patients before treatment were significantly lower than in the healthy controls (22.2 +/-3.8 micromol/L) and those measured at the remission stage (21.0 +/- 3.5 micromol/L) (P < 0.01). Serum transferrin levels in NS patients before therapy (1.9 +/- 0.3 g/L) also decreased compared with those in the healthy controls (3.1 +/- 0.5 g/L) and those measured at the remission stage (2.9 +/- 0.6 g/L) (P < 0.01). In contrast, serum total iron-binding capacity and transferrin saturation were noticeably higher in NS patients before treatment than those in the healthy controls (total iron-binding capacity 56.4 +/- 9.2 micromol/L vs 50.7 +/- 6.8 micromol, P < 0.01; transferrin saturation 55.7 +/- 9.2 % vs 46.4 +/- 8.2%, P < 0.01) and were also higher than those measured at the remission stage (51.9 +/-7.7 micromol/L and 47.4 +/- 13.3%) (P < 0.01). Serum transferrin positively correlated to serum albumin (r = 0.609, P < 0.01) and negatively correlated to urinary transferrin (r = -0.550, P < 0.01) in NS patients before treatment. CONCLUSIONS: Serum iron and transferrin levels markedly decreased in NS patients, which may be partially related to the urinary loss of transferrin.

Adolescent↗

PubMed1984

Developmental changes in plasma transferrin concentrations related to red cell ferritin.

Transferrin, the plasma iron transport protein, has two iron-binding sites but is usually only partly saturated. (Essentially all plasma iron is bound to transferrin.) Thus, changes in transferrin saturation reflect differences in the concentrations of plasma iron and/or transferrin. Developmental changes in red cell ferritin content coincide with a 2.5 times increase in plasma transferrin and a proportional decrease in saturation, in the bullfrog model system. The possible relationship of the degree of transferrin saturation and structure on the distribution of iron between heme and ferritin was examined in suspensions of reticulocytes, which synthesize both ferritin and heme. The extra transferrin in adult plasma was indistinguishable from transferrin in tadpole plasma in terms of the ability to donate iron to red cell heme and ferritin in vitro and in terms of surface charge (pI 6.55, 6.34), molecular weight (73,000), carbohydrate content (2%), amino acid composition, and immunological reactivity. Only the saturation in vivo appeared to differ. When the saturation of transferrin was manipulated in vitro, an effect on the relative distribution of iron between heme and ferritin was observed. The heme-synthesizing system consumed a disproportionately large amount of the delivered iron until it was saturated, a point which coincided with transferrin saturation; as the degree of transferrin saturation decreases, iron delivered to red cell iron stores (ferritin) decreases disproportionately. Thus, the developmental increase in plasma transferrin and consequent decrease in saturation minimize the amount of iron available for storage in red cells. The effect is further enhanced by the decreased ability of adult erythrocytes to incorporate iron from transferrin, a property which may be related to quantitative changes observed in iodination of a Mr = 168,000 membrane protein.

Age Factors↗

PubMed1981

The behavior of transferrin iron in the rat.

The behavior of rat transferrin has been investigated employing acrylamide gel electrophoresis and isoelectric focusing. In vitro trace labeling with iron chelates at 30 min was 93%-98% effective, whereas binding by simple ferric salts was reduced to 71%-76%. Complete and specific binding of 59FeSO4 by the iron binding sites of transferrin was demonstrated after in vitro or in vivo addition of ferrous ammonium sulfate in pH 2 saline up to the point of iron saturation. In vitro the radioriron transferrin complex in plasma was stable and its iron had a negligible exchange with other transferrin binding sites over several hours. The distribution of radioiron added in vitro or through absorption was shown to be random between the binding sites of slow and fast transferrin molecule. Iron distribution among body tissues was similar for mono- and diferric transferrin iron and was not affected by the site distribution of iron on the transferrin molecule. The only important aspect of transferrin iron binding was the more rapid tissue uptake of iron in the diferric form was compared to monoferric transferrin. Additional in vivo effects on internal iron exchange were produced by changes in the iron balance of the animal. In the iron loaded animal, monoferric transferrin injected into the plasma was rapidly loaded by iron from tissue and thereby converted to diferric transferrin. Injection of diferric transferrin in the iron deficient animal was associated with a rapid disappearance from circulation of the original complex and a subsequent appearance of monoferric transferrin as a result of iron returning from tissues. These observations support the concept that plasma iron behaves as a single pool except that diferric iron exchange occurs at a more rapid rate than dose monoferric iron exchange.

Animals↗