Number Of Transferrin Receptors Research Articles

Abstract 451: Transferrin Receptor identifies a distinct pool of circulating tumor cells from metastatic prostate cancer patients with unique molecular profiles enriched in AR variants

Abstract Androgen receptor (AR) drives prostate cancer (PC) progression, even in castrate-conditions due to expression of AR variants (AR-V), which are constitutively active in the nucleus. Castration-resistant prostate cancer (CRPC) is currently lethal, due to the development of drug resistance. The molecular basis of clinical drug resistance remains poorly elucidated, due to tumor heterogeneity and limited availability of serial tumor sampling as disease progresses. Circulating tumor cells (CTCs), isolated from patient peripheral blood, have emerged as a reliable, easy to obtain source of tumor cells which can be and used to interrogate the molecular disease evolution. To date, EpCAM-based CTC enrichment is commonly used but has important shortcomings as EpCAM is often lost during EMT, thus, missing the more aggressive mesenchymal CTCs. On the other hand, Transferrin Receptor (TfR) which is overexpressed in cancer cells, is a cell surface protein required for iron uptake and is critical for several biological processes such as cell proliferation and metabolism. Mining large gene expression databases in PC we observed that TfR expression increased with disease stage, from adenocarcinoma (TCGA) to CRPC (SU2C) to the more aggressive neuroendocrine PC (NEPC), while EpCAM expression remained unchanged. We also found that TfR expression was increased in EMT cell models, while EpCAM expression was lost, suggesting that TfR may perform well in CTC isolation across the EMT spectrum. We then tested TfR- and EpCAM-based CTC enrichment in a cohort of 31 CRPC patients, where we observed a significantly higher number of TfR+ CTCs (median, 304) than EpCAM+-CTCs (median, 21) (p<0.01). RNA-sequencing of TfR+ CTCs in comparison to EpCAM+ CTCs, followed by gene-set enrichment analyses revealed that the TfR+ subpopulation was significantly enriched in prostate specific oncogenic pathways including EMT, suggesting distinct molecular profiles between the two subsets. To investigate the clinical relevance of the two CTC subsets, we quantitated AR-FL and splice variants AR-V7 and AR-v567es expression by digital droplet PCR (ddPCR) in pools of TfR+-CTCs vs EpCAM+-CTCs. Our results from 16 CRPC patients showed that while expression of AR-FL was similar in the two CTC subsets, both AR variants were enriched in TfR+-CTCs. To better map the tumor heterogeneity of AR-V expression we isolated 102 single TfR+- and 63 single EpCAM+-CTCs from 3 CRPC patients and quantified AR-V expression by ddPCR. The single CTC analysis revealed that AR-V7 and AR-v567es were expressed in 21% and 18% of TfR+-CTCs, respectively, vs 0% in EpCAM+-CTCs. These data identify TfR as a promising marker for CTC identification across the EMT gradient, and provide a unique insight into tumor cell heterogeneity, which was not appreciated before, and which may have significant clinical impact. [A. Gjyrezi and G. Galletti contributed equally to this work.] Citation Format: Ada Gjyrezi, Giuseppe Galletti, Jiaren Zhang, Rohan Bareja, Ahmed Halima, Daniel Worroll, David Nanus, Scott Tagawa, Himisha Beltran, Paraskevi Giannakakou. Transferrin Receptor identifies a distinct pool of circulating tumor cells from metastatic prostate cancer patients with unique molecular profiles enriched in AR variants [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 451.

Progress on anti-tumor molecular mechanisms of dihydroartemisinin

Artemisinin is an anti-malarial drug with poor water solubility and oral absorption; so a variety of derivatives based on the parent nucleus have been developed. Compared with artemisinin, dihydroartemisinin (DHA) has a stronger anti-malaria activity, and has the advantages of high metabolic rate and better water solubility. Recent studies have discovered that DHA has a good inhibitory effect on tumor cells, which is closely related to the peroxide bridge in its molecular structure. Since tumor cells need more Fe3+ than normal cells, there are a large number of transferrin receptors on the tumor cell membrane. DHA can break the peroxide bridge in the presence of Fe2+, and the free radicals generated can play its lethal effect on tumor cells. In addition, DHA can promote endocytosis of transferrin receptor, and thus prevent cancer cells from taking Fe3+ from microenvironment. This article reviews the anti-tumor molecular mechanism of DHA, including accelerating oxidative damage, inducing apoptosis, inhibiting the growth, proliferation and invasion of tumor cells, reversing tumor multidrug resistance.

A Numerical Method for Structured Population Equations Modeling Control of Erythropoiesis

Population equations with more than one structuring attribute play an essential role in modeling cell populations important for the process of erythropoiesis. Attributes in this case are cell age, iron content of cells and number of transferrin receptors on the cell membrane. The system is controlled via a feedback control using the oxygen carrying capacity of blood (which is determined by the number of red blood cells) as input for the controller and erythropoietin secreted by the kidneys as control for the system. The numerical algorithm is based on Trotter-Kato type approximations of the system state by system states of high order ordinary differential equations on finite dimensional subspaces of the state space of the system. These finite dimensional subspaces are generated by Legendre polynomials.

High Levels of Zinc-Protoporphyrin Identify Iron Metabolic Abnormalities in Pulmonary Arterial Hypertension

Iron homeostasis influences the development of pulmonary arterial hypertension (PAH) associated with hypoxia or hematologic disorders. To investigate whether severity of idiopathic PAH (IPAH) is impacted by alterations in iron metabolism, we assessed iron metabolic markers, including levels of zinc-protoporphyrin (Zn-pp), transferrin receptor, and red blood cell numbers and morphology in IPAH, associated PAH and sleep apnea-induced pulmonary hypertension patients in comparison to healthy controls and asthmatics. Despite similarly normal measures of iron metabolism, Zn-pp levels in IPAH and sleep apnea patients were elevated approximately twofold, indicating deficient iron incorporation to form heme and levels were closely related to measures of disease severity. Consistent with high Zn-pp, PAH patients had increased red cell distribution width (RDW). In an expanded cohort including patients with IPAH and familial disease, the RDW was validated and related to clinical parameters of severity; including pulmonary artery pressures and 6-minute walk distances. These results reveal an increased prevalence of subclinical functional iron deficiency in primary forms of PAH that is quantitatively related to disease severity. This suggests that altered iron homeostasis influences disease progression and demonstrates the importance of closely monitoring iron status in PAH patients.

Doxorubicin-transferrin conjugate selectively overcomes multidrug resistance in leukaemia cells

Neoplastic cells frequently have an increased number of transferrin receptors. Coupling transferrin to an anti-neoplastic drug has the potential to overcome multidrug resistance (MDR). The purpose of this study was to examine the distribution and action of doxorubicin-transferrin conjugate (DOXTRF) in a leukaemia cell line (HL60), a multidrug-resistant leukaemia cell line (HL60ADR) and a normal tissue cell line (human fibroblasts). The intracellular accumulation of DOX and DOX-TRF was monitored by direct fluorescence. More DOX-TRF than free DOX was delivered to the tumour cells, and consecutively the levels of DNA double-strand breaks and apoptosis increased even in the multidrug-resistant cell line. In the normal tissue cell line, DOX-TRF did not accumulate, and therefore, the levels of DNA double-strand breaks and apoptosis did not increase. Cell viability was determined using the MTT assay. The IC50 for DOX-TRF was lower than the IC50 value for the free drug in both leukaemia cell lines. The IC50 values for the HL60 cells were 0.08 μM for DOX and 0.02 μM for DOX-TRF. The IC50 values for HL60ADR cells were 7 μM for DOX and 0.035 μM for DOX-TRF. In conclusion, DOX-TRF was able to overcome MDR in the leukaemia cell lines while having only a very limited effect on normal tissue cells.

SiRNA screen of the human signaling proteome identifies the PtdIns(3,4,5)P3-mTOR signaling pathway as a primary regulator of transferrin uptake

A survey of 1,804 human dicer-generated signaling siRNAs using automated quantitative imaging identified the phosphatidylinositol-3,4,5-trisphosphate-mTOR signaling pathway as a primary regulator of iron-transferrin uptake.

Gallium-induced cell death in lymphoma: role of transferrin receptor cycling, involvement of Bax and the mitochondria, and effects of proteasome inhibition

Gallium nitrate is a metallodrug with clinical efficacy in non-Hodgkin's lymphoma. Its mechanisms of antineoplastic action are not fully understood. In the present study, we investigated the roles of transferrin receptor (TfR) targeting and apoptotic pathways in gallium-induced cell death. Although DoHH2 lymphoma cells displayed a 3-fold lower number of TfRs than CCRF-CEM lymphoma cells, they were 3- to 4-fold more sensitive to gallium nitrate. Despite a lower TfR expression, DoHH2 cells had greater TfR cycling and iron and gallium uptake than CCRF-CEM cells. In other lymphoma cell lines, TfR levels per se did not correlate with gallium sensitivity. Cells incubated with gallium nitrate showed morphologic changes of apoptosis, which were decreased by the caspase inhibitor Z-VAD-FMK and by a Bax-inhibitory peptide. Cells exposed to gallium nitrate released cytochrome c from mitochondria and displayed a dose-dependent increase in caspase-3 activity. An increase in active Bax levels without accompanying changes in Bcl-2 or Bcl-X(L) was seen in cells incubated with gallium nitrate. The endogenous expression of antiapoptotic Bcl-2 was greater in DoHH2 cells than in CCRF-CEM cells, suggesting that endogenous Bcl-2 levels do not correlate with cell sensitivity to gallium nitrate. Gallium-induced apoptosis was enhanced by the proteasome inhibitor bortezomib. Our results suggest that TfR function rather than TfR number is important in gallium targeting to cells and that apoptosis is triggered by gallium through the mitochondrial pathway by activating proapoptotic Bax. Our studies also suggest that the antineoplastic activity of combination gallium nitrate and bortezomib warrants further investigation.

Dynasore, a Cell-Permeable Inhibitor of Dynamin

Dynamin is essential for clathrin-dependent coated vesicle formation. It is required for membrane budding at a late stage during the transition from a fully formed pit to a pinched-off vesicle. Dynamin may also fulfill other roles during earlier stages of vesicle formation. We have screened about 16,000 small molecules and have identified 1, named here dynasore, that interferes in vitro with the GTPase activity of dynamin1, dynamin2, and Drp1, the mitochondrial dynamin, but not of other small GTPases. Dynasore acts as a potent inhibitor of endocytic pathways known to depend on dynamin by rapidly blocking coated vesicle formation within seconds of dynasore addition. Two types of coated pit intermediates accumulate during dynasore treatment, U-shaped, half formed pits and O-shaped, fully formed pits, captured while pinching off. Thus, dynamin acts at two steps during clathrin coat formation; GTP hydrolysis is probably needed at both steps.

Transferrin-conjugated liposome/IL-12 pDNA complexes for cancer gene therapy in mice

Transferrin (Tf) has been used as a targeting ligand for delivering liposome/interleukin-12 (IL-12) pDNA complexes to cancer cells mostly due to the greater number of transferrin receptors (TfR) found on tumor cells than on normal cells. Tf was conjugated to liposomes via the reaction of MPB-PE with thiol groups of Tf introduced by a heterobifunctional cross-linking agent,N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP). Four days after C-26 inoculation when the tumor volume reached ∼100 mm3, tumor-bearing Balb/c mice were injected intravenously with Tf -liposome/IL-12 pDNA complexes twice a week for 3 weeks. Significant suppression of tumor growth was achieved in the group treated with the Tf -liposome/IL-12 pDNA complexes, with a dose of 10 μg of IL-12 pDNA showing the highest suppression effect among the tested doses. Similar results were obtained when the therapy was initiated one day after tumor inoculation, although in this case 30 μg IL-12 pDNA/Tf -liposome complexes showed a significant suppression of tumor growth between 19 and 23 days after tumor inoculation. This result indicates that the transferrin receptor-targeted liposomal system is an efficient delivery agent of therapeutic genes, such as IL-12, in mice and that its potential clinical use warrants further research investigation.

Evaluation of transferrin-polyethylenimine conjugate for targeted gene delivery

With the aim to improve the specificity and to reduce the cytotoxicity of polyethylenimine (PEI), we have synthesized the conjugates of the branched PEI (25 kDa) with transferrin. The transferrin-PEI (TP) conjugates with five compositions were synthesized using periodate oxidation method and confirmed by FT-IR spectroscopy and gel permeation chromatography. The free amine contents of TP conjugates, which were able to condense and deliver DNA, increased as the amount of PEI increased. TP/DNA polyplexes were characterized by measuring gel electrophoresis, ethidium bromide fluorescence quenching, particle size and zeta potential of complexes. Complete complexation of the polyplexes was observed above the N/P ratio of 5 in TP/ DNA, and above 3 in PEI/DNA, respectively. The zeta potential of the complexes decreased as the amount of transferrin in TP conjugates increased. Transfection efficiency of TP conjugates was evaluated in HeLa cell and Jurkat cell systems. Among the five compositions of TP conjugates, TP-2 system mediated a higher beta-galactosidase gene expression than PEI system in Jurkat cell which was known to express elevated numbers of transferrin receptors. From the results of the cell viability based on MTT assay, TP conjugates showed lower cytotoxicity compared with the PEI system. We expect that the TP conjugate can be used efficiently as a nonviral gene delivery vector.

Effects of AZT on cellular iron homeostasis.

3'-azido-3'-deoxythymidine (AZT), the first chemotherapeutic drug approved by FDA for treatment of HIV-infected patients and still used in combination therapy, has been shown to induce, upon prolonged exposure, severe bone marrow toxicity manifested as anemia, neutropenia and siderosis. These toxic effects are caused by inhibition of heme synthesis and, as a consequence, transferrin receptor (TfR) number appears increased and so iron taken up by cells. Since iron overload can promote the frequency and severity of many infections, siderosis is viewed as a further burden for AIDS patients. We have previously demonstrated that AZT-treated K562 cells showed an increase of the number of TfRs located on the surface of the plasma membrane without affecting their biosynthesis, but slowing down their endocytotic pathway. In spite of the higher number of receptors on the plasma-membrane of AZT-treated cells, intracellular accumulation of iron showed a similar level in control and in drug-exposed cells. The chelating ability of AZT and of its phosphorylated derivatives, both in an acellular system and in K562 cells, was also checked. The results demonstrated that AZT and AZTMP were uneffective as iron chelators, while AZTTP displayed a significant capacity to remove iron from transferrin (Tf). Our results suggest that AZT may be not directly involved in the iron overloading observed upon its prolonged use in AIDS therapy. The iron accumulation found in these patients is instead caused by other unknown mechanisms that need further studies to be clarified.

Soluble Transferrin Receptor and Its Ratio to Erythroblasts in Bone Marrow May Be a New Diagnostic Tool to Distinguish between Aplastic and Refractory Anemia

Myelodysplastic syndromes (MDS), especially refractory anemia (RA) are very heterogeneous diseases regarding their morphological, biological and clinical features. One important clinical problem is the difficulty of diagnosis. Soluble transferrin receptors (sTfRs) reflect the erythropoietic activity in the bone marrow (BM). To establish whether determination of serum sTfR could be useful for the differential diagnosis between RA and aplastic anemia (AA), we measured the serum sTfR concentrations, BM cellularity and BM erythroblast percentages in 14 untreated AA and 7 untreated RA patients. The serum sTfR levels of the RA patients (820.1 ± 402.8 ng/ml) were significantly higher than those of the AA patients (491.1 ± 195.2 ng/ml; p = 0.0207). However, the serum sTfR values of RA and AA patients also overlapped. A new index, the ‘sTfR-E index’ [the ratio of serum sTfR level (ng/ml) to BM cellularity (%) × BM erythroblasts (%)] is proposed, which is expected to reflect the number of transferrin receptors (TfR) on the cell membrane per BM erythroblast. The sTfR-E index values of the 7 RA patients (0.395 ± 0.234) were significantly lower than those of the 14 AA patients (2.669 ± 1.633; p = 0.0003). The sTfR-E index values of AA and RA patients overlapped only marginally. In conclusion, the sTfR-E index may be a useful new diagnostic tool to distinguish between AA and RA patients.

Screening for iron deficiency.

1. Ann Chen Wu, MD* 2. Leann Lesperance, MD, PhD* 3. Henry Bernstein, DO*† 1. *Pediatric Health Associates, Hunnewell Ground Children’s Hospital 2. †Associate Professor of Pediatrics, Harvard Medical School, Boston, MA After completing this article, readers should be able to: 1. Determine the most common cause of iron deficiency in the United States. 2. Describe the pathogenesis of iron deficiency. 3. List populations at high risk for iron deficiency. 4. Outline the common signs and symptoms of iron deficiency. 5. Specify the American Academy of Pediatrics recommendations for screening for iron deficiency. In the March and April issues of Pediatrics in Review, we published a two-part article on managing anemia in a pediatric office practice. This article expands on the various tests for iron deficiency, including some relatively new ones. These articles should be read as complementary.—RJH Iron deficiency is the most common nutritional deficiency in the world, responsible for a staggering amount of ill health, lost productivity, and premature death. Although its prevalence in the United States has declined since the late 1960s, iron deficiency with or without anemia still is seen frequently in infants, toddlers, adolescent females, and women of childbearing age. In fact, iron deficiency anemia remains the most common hematologic disease of infants and children. Anemia is defined as a low hemoglobin (Hgb) concentration or red blood cell (RBC) mass compared with age-specific norms. Anemia may be caused by decreased RBC production, increased RBC destruction, or blood loss. Based on the size of the RBC, hematologists categorize anemia as macrocytic, normocytic, or microcytic. Iron is found in different compartments within the body. Total body iron (measured by ferritin), transport iron (measured by transferrin saturation), serum iron, and other hematologic and biochemical markers are used to describe the degrees of iron deficiency. Iron depletion refers to the earliest stage of diminishing iron stores in the setting of insufficient iron supply. Iron deficiency (without anemia) develops as these iron stores are depleted further and begin to impair Hgb synthesis. Finally, iron deficiency anemia results …

Effect of different durations of exercise on transferrin-bound iron uptake by rat erythroblast

This study evaluated effects of different durations of exercise on transferrin receptor (TfR) expression on the membrane of rat erythroblasts. Female rats were assigned to six groups: 3, 6 and 12 months of strenuous exercise (swimming 2 h/day, 5 days/wk) groups and their corresponding controls. At the end of experiments, the erythroblasts were isolated for Tf binding assay and transferrin-bound iron (Tf-Fe) uptake. Tissue non-heme iron and hematological iron indices were also measured. The TfR number on the cells was about 603,189 ± 107,562, 890,150 ± 164,849 and 384,695 ± 46,295 molecules/cell in three control groups (3, 6, 12 months) respectively. Exercise groups had significantly higher levels of TfR than those of the control groups, being 1,374,137 ± 243,677, 2,175,360 ± 462,737 and 1,012,759 ± 249,423 molecules/cell in 3, 6 and 12 months of exercise groups respectively (p < 0.05). After 30 min of incubation, cellular Tf approached to levels of 8.28 ± 1.94, 10.73 ± 3.30 and 6.60 ± 0.93 fmole/10 6 cells in 3, 6 and 12 months of exercise groups, while the corresponding control values were 3.09 ± 0.36, 5.03 ± 1.01 and 2.51 ± 0.88 fmole/10 6 cells respectively (all P < 0.05). The rates of cellular iron accumulation were 7.07 (3), 8.79 (6) and 5.96 (12 month) fmole/10 6 cells/min in the exercised rats and 2.91, 3.85, and 2.03 fmole/10 6 cells/min in their corresponding controls (all p < 0.05). However, no significant difference was observed in the ratios (Exercise/Corresponding control) of the increased TfR expression, Tf-Fe uptake and Tf endocytosis as well as of the decreased plasma iron and tissue non-heme iron levels induced by different periods of exercise. Furthermore, the increase in the length of exercise (6 or 12 month) did not induce a remarkable decrease in plasma hemoglobin and hematocrit. These results indicate that a true iron deficiency or ‘sport anemia’ can not develop even if under longer periods (6 or 12 month) of strenuous exercise.

Iron transport in a lymphoid cell line with the hemochromatosis C282Y mutation

AbstractThe gene for hemochromatosis (HFE) is expressed in a variety of cells, including those not thought to be affected by this disease. The impact of HFE on iron transport was examined in B-lymphoid cell lines developed from a patient with hemochromatosis with the HFE C282Y mutation (C282Y cells) and an individual with the wild-type HFE gene (WT cells). Whereas both cell lines expressed HFE protein, C282Y cells displayed less HFE protein at the cell surface. Transferrin receptor (TfR) number was 2- to 3-fold greater in WT cells than in C282Y cells, while TfR affinity for transferrin (Tf) was slightly lower in C282Y cells. TfR distribution between intracellular and cell-surface compartments was similar in both cell lines. Iron uptake per cell was greater in WT cells but was not increased proportional to TfR number. When considered relative to cell-surface TfR number, however, iron uptake and Tf internalization were actually greater in C282Y cells. Surprisingly, Tf-independent iron uptake was also significantly greater in C282Y cells than in WT cells. The ferritin content of C282Y cells was approximately 40% that of WT cells. Exposure of cells to pro-oxidant conditions in culture led to a greater inhibition of proliferation in C282Y cells than in WT cells. Our results indicate that in this B-lymphoid cell line, the HFE C282Y mutation affects both Tf-dependent and -independent iron uptake and enhances cell sensitivity to oxidative stress. The role of HFE in iron uptake by B cells may extend beyond its known interaction with the TfR.

Overexpression of hemochromatosis protein, HFE, alters transferrin recycling process in human hepatoma cells

HFE is a MHC class 1-like protein that is mutated in hereditary hemochromatosis. In order to elucidate the role of HFE protein on cellular iron metabolism, functional studies were carried out in human hepatoma cells (HLF) overexpressing a fusion gene of HFE and green fluorescent protein (GFP). The expression of HFE-GFP was found to be localized on cell membrane and perinuclear compartment by fluorescent microscopy. By co-immunoprecipitation and Western blotting, HFE-GFP protein formed a complex with endogenous transferrin receptor and β 2-microglobulin, suggesting that this fusion protein has the function of HFE reported previously. We then examined the 59Fe uptake and release, and internalization and recycling of 125I-labeled transferrin in order to elucidate the functional roles of HFE in the cell system. In the transfectants, HFE protein decreased the rate of transferrin receptor-dependent iron ( 59Fe) uptake by the cells, but did not change the rate of iron release, indicating that HFE protein decreased the rate of iron influx. Scatchard analysis of transferrin binding to HFE-transfected cells showed an elevation of the dissociation constant from 1.9 to 4.3 nM transferrin, indicating that HFE protein decreased the affinity of transferrin receptor for transferrin, while the number of transferrin receptors decreased from 1.5×10 5/cell to 1.2×10 5/cell. In addition, the rate of transferrin recycling, especially return from endosome to surface, was decreased in the HFE-transfected cells by pulse-chase study with 125I-labeled transferrin. Our results strongly suggest an additional role of HFE on transferrin receptor recycling in addition to the decrease of receptor affinity, resulting in the reduced cellular iron.

Aberrantly low transferrin receptor expression on human monocytes is associated with nonpermissiveness for Legionella pneumophila growth.

Growth of Legionella pneumophila within human monocytes is iron dependent. A person with monocytes uniquely nonpermissive to L. pneumophila growth was identified whose monocytes expressed an abnormally low number of transferrin receptors in the nonactivated state, similar to the typically low level expressed in the interferon-gamma-activated state. The monocytes failed to up-regulate transferrin receptor expression appropriately in response to iron-transferrin. After treatment for chronic periodontal disease, the subject's monocytes converted to a permissive state. In contrast to the nonpermissive state, the permissive monocytes had normal transferrin receptor expression and up-regulated transferrin receptor expression appropriately in response to iron-transferrin. Thus, a nonpermissive state for L. pneumophila intracellular multiplication is associated with low levels of transferrin receptor expression in nonactivated monocytes and with an inability to up-regulate transferrin receptor expression in response to iron-transferrin. This nonpermissive state may be related to chronic inflammatory conditions such as periodontal disease.

Cell-type specific protoporphyrin IX metabolism in human bladder cancer in vitro.

5-Aminolevulinic acid (ALA)-supported fluorescence endoscopy of the urinary bladder results in a detection rate of bladder cancer superior to that of white light endoscopy. The different accumulation of the metabolite protoporphyrin IX (PPIX) in tumor cells after ALA instillation is poorly understood; however, it is crucial to optimize diagnosis and potential phototherapy. For systematic analysis of cell-type specific PPIX accumulation and metabolism two human bladder carcinoma cell lines (RT4 and J82), a normal urothelial cell line (UROtsa), and a fibroblast cell line (N1) were chosen, and grown in two different growth states to model important tissue components of the urinary bladder, i.e. tumor, normal epithelium and stroma. To quantitate PPIX content, fluorescence intensities measured by flow cytometry were matched with cellular PPIX extraction values, and related to relative ferrochelatase activity, cellular iron content, number of transferrin receptors per cell and porphobilinogen deaminase (PBGD) activity. For in vitro experiments, the initial correlation of relative flow cytometric and spectrometric measurements of PPIX provides a calibration curve for consequent flow cytometric PPIX quantification. Lower fluorescence of normal cells could be explained by significant differences of ferrochelatase activity and iron content in comparison to tumor cells. However, the content of iron was not related to transferrin receptor content. PBGD activity seemed to play a minor role for the differential accumulation of PPIX in urothelial cells. In conclusion, the in vitro culture of urothelial cells and fibroblasts indicates that the most important metabolic step for PPIX accumulation in the urinary bladder is the transition from PPIX to heme. Further investigation of PPIX metabolism does support the validation of photodynamic diagnosis, and might also lead the way to a highly specific tumor related molecule.

Transferrin and transferrin receptor function in brain barrier systems.

1. Iron (Fe) is an essential component of virtually all types of cells and organisms. In plasma and interstitial fluids, Fe is carried by transferrin. Iron-containing transferrin has a high affinity for the transferrin receptor, which is present on all cells with a requirement for Fe. The degree of expression of transferrin receptors on most types of cells is determined by the level of Fe supply and their rate of proliferation. 2. The brain, like other organs, requires Fe for metabolic processes and suffers from disturbed function when a Fe deficiency or excess occurs. Hence, the transport of Fe across brain barrier systems must be regulated. The interaction between transferrin and transferrin receptor appears to serve this function in the blood-brain, blood-CSF, and cellular-plasmalemma barriers. Transferrin is present in blood plasma and brain extracellular fluids, and the transferrin receptor is present on brain capillary endothelial cells, choroid plexus epithelial cells, neurons, and probably also glial cells. 3. The rate of Fe transport from plasma to brain is developmentally regulated, peaking in the first few weeks of postnatal life in the rat, after which it decreases rapidly to low values. Two mechanisms for Fe transport across the blood-brain barrier have been proposed. One is that the Fe-transferrin complex is transported intact across the capillary wall by receptor-mediated transcytosis. In the second, Fe transport is the result of receptor-mediated endocytosis of Fe-transferrin by capillary endothelial cells, followed by release of Fe from transferrin within the cell, recycling of transferrin to the blood, and transport of Fe into the brain. Current evidence indicates that although some transcytosis of transferrin does occur, the amount is quantitatively insufficient to account for the rate of Fe transport, and the majority of Fe transport probably occurs by the second of the above mechanisms. 4. An additional route of Fe and transferrin transport from the blood to the brain is via the blood-CSF barrier and from the CSF into the brain. Iron-containing transferrin is transported through the blood-CSF barrier by a mechanism that appears to be regulated by developmental stage and iron status. The transfer of transferrin from blood to CSF is higher than that of albumin, which may be due to the presence of transferrin receptors on choroid plexus epithelial cells so that transferrin can be transported across the cells by a receptor-mediated process as well as by nonselective mechanisms. 5. Transferrin receptors have been detected in neurons in vivo and in cultured glial cells. Transferrin is present in the brain interstitial fluid, and it is generally assumed that Fe which transverses the blood-brain barrier is rapidly bound by brain transferrin and can then be taken up by receptor-mediated endocytosis in brain cells. The uptake of transferrin-bound Fe by neurons and glial cells is probably regulated by the number of transferrin receptors present on cells, which changes during development and in conditions with an altered iron status. 6. This review focuses on the information available on the functions of transferrin and transferrin receptor with respect to Fe transport across the blood-brain and blood-CSF barriers and the cell membranes of neurons and glial cells.

Iron deficiency in children: detection and prevention.

Iron deficiency in children: detection and prevention.