Immunological Reactivity of Serum Ferritin in Patients with Malignancy

Interactions of ferritin with scavenger receptor class A members

Scavenger receptors are a superfamily of membrane-bound receptors that recognize both self and nonself targets. Scavenger receptor class A (SR-A) has five known members (SCARA1 to -5 or SR-A1 to -A5), which are type II transmembrane proteins that form homotrimers on the cell surface. SR-A members recognize various ligands and are involved in multiple biological pathways. Among them, SCARA5 can function as a ferritin receptor; however, the interaction between SCARA5 and ferritin has not been fully characterized. Here, we determine the crystal structures of the C-terminal scavenger receptor cysteine-rich (SRCR) domain of both human and mouse SCARA5 at 1.7 and 2.5 Å resolution, respectively, revealing three Ca²⁺-binding sites on the surface. Using biochemical assays, we show that the SRCR domain of SCARA5 recognizes ferritin in a Ca²⁺-dependent manner, and both L- and H-ferritin can be recognized by SCARA5 through the SRCR domain. Furthermore, the potential binding region of SCARA5 on the surface of ferritin is explored by mutagenesis studies. We also examine the interactions of ferritin with other SR-A members and find that SCARA1 (SR-A1, CD204) and MARCO (SR-A2, SCARA2), which are highly expressed on macrophages, also interact with ferritin. By contrast, SCARA3 and SCARA4, the two SR-A members without the SRCR domain, have no detectable binding with ferritin. Overall, these results provide a mechanistic view regarding the interactions between the SR-A members and ferritin that may help to understand the regulation of ferritin homeostasis by scavenger receptors.

Ferritin in Kidney and Vascular Related Diseases: Novel Roles for an Old Player

Iron is at the forefront of a number of pivotal biological processes due to its ability to readily accept and donate electrons. However, this property may also catalyze the generation of free radicals with ensuing cellular and tissue toxicity. Accordingly, throughout evolution numerous pathways and proteins have evolved to minimize the potential hazardous effects of iron cations and yet allow for readily available iron cations in a wide variety of fundamental metabolic processes. One of the extensively studied proteins in the context of systemic and cellular iron metabolisms is ferritin. While clinicians utilize serum ferritin to monitor body iron stores and inflammation, it is important to note that the vast majority of ferritin is located intracellularly. Intracellular ferritin is made of two different subunits (heavy and light chain) and plays an imperative role as a safe iron depot. In the past couple of decades our understanding of ferritin biology has remarkably improved. Additionally, a significant body of evidence has emerged describing the significance of the kidney in iron trafficking and homeostasis. Here, we briefly discuss some of the most important findings that relate to the role of iron and ferritin heavy chain in the context of kidney-related diseases and, in particular, vascular calcification, which is a frequent complication of chronic kidney disease.

Measurement of Ferritin-Bearing Lymphocytes in Man. Preliminary Studies on the Use of Monoclonal Antibodies Specific for the L and H Subunits of Ferritin

We used the monoclonal antibodies LFO3 (specific for the L subunit of ferritin) and 2A4 (specific for the H subunit) in an indirect immunofluorescence test for enumerating ferritin-bearing lymphocytes (FBL). In 13 normal subjects, the geometric mean value of FBL was 4 % (range 0–13 %) with the monoclonal antibody LFO3, and 3 % (range 0–8 %) with the monoclonal antibody 2A4. Values in 5 subjects with transfusional iron overload and increased plasma L-type ferritin concentration were 5 % (4–7 %) and 3 % (2–4 %), respectively, which is similar to those in normal subjects. Thirteen patients with malignant disease had normal to increased values for plasma ferritin; the circulating protein was largely of L-type with undetectable or very low concentrations of H-type ferritin. In the same patients, the percentage of FBL was greater with the monoclonal antibody 2A4 (geometric mean value 8 %; range 3–12 %) than with the monoclonal antibody LFO3 (geometric mean value 3 %; range, 1–7 %). It is concluded that acidic and basic isoferritins can be differently expressed on the surface of peripheral blood lymphocytes, and that the monoclonal 2A4 could be particularly useful in the measurement of FBL in patients with malignancy.

Biology of ferritin in mammals: an update on iron storage, oxidative damage and neurodegeneration

Iron is an abundant transition metal that is essential for life, being associated with many enzyme and oxygen carrier proteins involved in a variety of fundamental cellular processes. At the same time, the metal is potentially toxic due to its capacity to engage in the catalytic production of noxious reactive oxygen species. The control of iron availability in the cells is largely dependent on ferritins, ubiquitous proteins with storage and detoxification capacity. In mammals, cytosolic ferritins are composed of two types of subunits, the H and the L chain, assembled to form a 24-mer spherical cage. Ferritin is present also in mitochondria, in the form of a complex with 24 identical chains. Even though the proteins have been known for a long time, their study is a very active and interesting field yet. In this review, we will focus our attention to mammalian cytosolic and mitochondrial ferritins, describing the most recent advancement regarding their storage and antioxidant function, the effects of their genetic mutations in human pathology, and also the possible involvement in non-iron-related activities. We will also discuss recent evidence connecting ferritins and the toxicity of iron in a set of neurodegenerative disorder characterized by focal cerebral siderosis.

The prognostic significance of elevated levels of serum ferritin before chemotherapy in patients with non-Hodgkin lymphoma

BACKGROUND

Elevated levels of serum ferritin have been documented to be an adverse prognostic factor in patients with hematologic malignancies undergoing hematopoietic stem cell transplantation. The purpose of this study was to estimate the correlation between elevated levels of serum ferritin and survival outcomes in patients with non-Hodgkin lymphoma (NHL).

PATIENTS AND METHODS

A total of 267 patients who were newly diagnosed with NHL and who received chemotherapy between September 1999 and April 2012 were retrospectively analyzed.

RESULTS

In multivariate analysis, other chemotherapy regimens excluding CHOP-like chemotherapy regimens (cyclophosphamide, adriamycin, vincristine, prednisolone) and RCHOP (rituximab plus CHOP), a high level of β2-microglobulin, a high-intermediate/high risk according to the international prognostic index (IPI), and elevated levels of serum ferritin were all significant independent prognostic factors for 5-year progression-free survival rates. RCHOP and other chemotherapy regimens, a high level of β2-microglobulin, a high-intermediate/high IPI risk, and high levels of serum ferritin were significant independent prognostic factors for 5-year overall survival rates.

CONCLUSION

Elevated levels of serum ferritin of 500 ng/mL or more as well as the use of chemotherapy regimens besides CHOP-like or RCHOP, a high-intermediate/high risk IPI, and a high level of beta2-microglobulin in NHL may be an important marker for predicting poor survival outcomes.

Human ferritin for tumor detection and therapy

Ferritin, a major iron storage protein found in most living organisms, is composed of a 24-subunit protein cage with a hollow interior cavity. Serum ferritin serves as a critical marker to detect total body iron status. However, recent research reveals a number of novel functions of ferritin besides iron storage; for example, a ferritin receptor, transferrin receptor 1 (TfR1), has been identified and serum ferritin levels are found to be elevated in tumors. A particular new finding is that magnetoferritin nanoparticles, biomimetically synthesized using H-chain ferritin to form a 24-subunit cage with an iron oxide core, possess intrinsic dual functionality, the protein shell specifically targeting tumors and the iron oxide core catalyzing peroxidase substrates to produce a color reaction allowing visualization of tumor tissues. Here we attempt to summarize current research on ferritin, particularly newly identified functions related to tumors, in order to address current challenges and highlight future directions.

Iron uptake mediated by binding of H-ferritin to the TIM-2 receptor in mouse cells

Ferritin binds specifically and saturably to a variety of cell types, and recently several ferritin receptors have been cloned. TIM-2 is a specific receptor for H ferritin (HFt) in the mouse. TIM-2 is a member of the T cell immunoglobulin and mucin domain containing (TIM) protein family and plays an important role in immunity. The expression of TIM-2 outside of the immune system indicates that this receptor may have broader roles. We tested whether ferritin binding to TIM-2 can serve as an iron delivery mechanism. TIM-2 was transfected into normal (TCMK-1) mouse kidney cells, where it was appropriately expressed on the cell surface. HFt was labeled with ⁵⁵Fe and ⁵⁵Fe-HFt was incubated with TIM-2 positive cells or controls. ⁵⁵Fe-HFt uptake was observed only in TIM-2 positive cells. HFt uptake was also seen in A20 B cells, which express endogenous TIM-2. TIM-2 levels were not increased by iron chelation. Uptake of ⁵⁵Fe-HFt was specific and temperature-dependent. HFt taken up by TIM-2 positive cells transited through the endosome and eventually entered a lysosomal compartment, distinguishing the HFt pathway from that of transferrin, the classical vehicle for cellular iron delivery. Iron delivered following binding of HFt to TIM-2 entered the cytosol and became metabolically available, resulting in increased levels of endogenous intracellular ferritin. We conclude that TIM-2 can function as an iron uptake pathway.

Serum ferritin: Past, present and future

BACKGROUND

Serum ferritin was discovered in the 1930s, and was developed as a clinical test in the 1970s. Many diseases are associated with iron overload or iron deficiency. Serum ferritin is widely used in diagnosing and monitoring these diseases.

SCOPE OF REVIEW

In this chapter, we discuss the role of serum ferritin in physiological and pathological processes and its use as a clinical tool.

MAJOR CONCLUSIONS

Although many aspects of the fundamental biology of serum ferritin remain surprisingly unclear, a growing number of roles have been attributed to extracellular ferritin, including newly described roles in iron delivery, angiogenesis, inflammation, immunity, signaling and cancer.

GENERAL SIGNIFICANCE

Serum ferritin remains a clinically useful tool. Further studies on the biology of this protein may provide new biological insights.

Ferritin excretion and iron balance in humans

Under normal circumstances, most of the lumenal iron taken into the intestinal mucosal cell is stored within the cell as ferritin and subsequently is lost in the faeces when the cell exfoliates at the end of its lifespan. To evaluate whether faecal iron proteins reflect mucosal cell iron as well as whole body iron and to examine further the kinetics of gastrointestinal iron transport, faecal H-rich and L-rich ferritin were measured in normal subjects and patients with iron deficiency and genetic haemochromatosis. In normal and iron-deficient subjects, the concentration of L-rich but not H-rich faecal ferritin correlated closely with body iron status. In genetic haemochromatosis, the faecal L-rich and H-rich ferritin concentrations were lower than expected for their body iron status. The administration of oral iron to normal subjects led to a rise in L-rich ferritin. Administration of oral or parenteral iron to patients with iron deficiency led to a prompt rise in both forms of faecal ferritin, although the relative increase of L-rich ferritin was greater than that of H-rich ferritin with oral iron administration. Faecal ferritin correlated closely with iron stores in normals and patients with iron deficiency but faecal ferritin levels were lower than expected in genetic haemochromatosis, similar to that previously noted in the duodenal mucosal cells of these patients.

Relationship of serum and tumor levels of iron and iron-binding proteins to lymphocyte immunity against tumor antigen in breast cancer patients

Fifty-two breast cancer patients were evaluated for levels of several molecules related to iron metabolism including determining their tumor tissue and serum ferritin levels, serum transferrin levels, and serum iron levels. In addition the patients' lymphocyte immunity against autologous tumor antigen was investigated. Forty percent (21 of 52) of the patients had lymphocyte immunity against tumor antigen. Iron metabolism molecules were expressed in abnormal quantities in some breast cancer patients: 27% (13 of 49) had elevated tumor tissue ferritin levels, 4% (2 of 49) had abnormally high serum ferritin, 10% (5 of 49) had abnormally low serum transferrin levels, and 43% (21 of 49) had depressed serum iron levels. None of these abnormalities in iron metabolism are associated with tumor immunity. These iron metabolism molecules may be indicative of rates of cell proliferation or may influence growth of breast cancer cells, but do not appear to influence host lymphocyte immunity against tumor associated antigens.

Serum ferritin in thyroid cancer

Serum ferritin, one of the nonspecific tumor markers, was studied in 102 thyroid cancer patients, who had been thyroidectomized and were off thyroxine for 1 month, making them hypothyroid. Serum ferritin in thyroid cancer patients was not significantly different as compared to controls. Nevertheless, high levels of serum ferritin were observed in the thyroid cancer group as compared to primary hypothyroid patients. Furthermore, there was a significant difference in serum ferritin between thyroid cancer patients without metastasis and those with metastasis, patients with metastasis showing higher levels. Classification of thyroid cancer patients into different histological types revealed higher ferritin levels in follicular carcinoma as compared to papillary carcinoma. These data suggest that, although serum ferritin may not be a tumor marker for thyroid cancer, this parameter seems to be sensitive to the presence of metastasis and the histologic diagnosis.

Cytosol and serum ferritin in breast carcinoma

This study was undertaken to determine tissue and serum ferritin levels in different stages of breast carcinoma. Eighty-nine cases have been evaluated, the groups investigated being breast carcinoma, benign breast disease and healthy controls. Ferritin levels in both the sera and the tissue cytosols were measured by an enzyme immunoassay method, while total proteins were assayed by Lowry's procedure and the ferritin concentrations given in ng ferritin/mg cytosol protein. No significant difference has been determined for serum ferritin between any of the groups studied, while the tissue cytosol ferritins were found to be 91.6 +/- 50.9, 565.0 +/- 48.3, 142.7 +/- 93.3, 683.3 +/- 212.9 and 655.5 +/- 100.4 ng/mg cytosol protein for the benign, malign (global), malign (stage I), malign (stage II) and malign (stage III) groups, respectively. The differences between the malign groups and the benign group were found to be highly significant (P < 0.001) except for the stage I subgroup, which was fairly significant (P < 0.05). A sensitivity of 90% was evaluated for tissue cytosol ferritin in breast carcinoma, the 'intra-patient' sensitivity being 100%. In conclusion, we state that tissue ferritin is more valuable than serum ferritin as a tumour marker of diagnosis for breast carcinoma.

Early and late hyperferremia during cisplatin chemotherapy

Changes in plasma iron levels were evaluated in 48 neoplastic patients receiving a total of 56 courses of polychemotherapy in which high doses of cisplatin were administered on day 1. Serum iron showed a three-fold mean increase 24 hours after cisplatin infusion, rising from a basal mean value of 78.25 +/- 45.74 micrograms/dl to 242.12 +/- 72.67 micrograms/dl (P less than 0.001). Hyperferremia began to lower after the 3rd day and pretreatment levels were again observed the 10th day. Ferritin increased progressively from a basal mean value of 565.81 +/- 435.18 micrograms/l to 928.73 +/- 665.41 micrograms/l the 7th day (P less than 0.001). Hemolysis and tissutal necrosis were excluded, since red cells, hemoglobin, muscular and hepatic enzymes and indirect bilirubin remained unmodified. Reticulocytes began to lower on the 3rd day and reached the nadir the 7th day: therefore the cisplatin-induced blockage of erythropoiesis, with consequent reduced iron use was maximum the 3rd day--as observed in animals by other Authors--and could not explain the early hyperferremia developing within 24 hours. Consequently hyperferremia seems to consist of two overlapping stages: an early stage by unknown interference of cisplatin on iron-loaded reticulo-endothelial cells, with consequent acute iron emissions into the blood stream; and a later stage by toxic effect of the drug on erythroid precursors with reduced iron uptake by bone marrow.

Tissue ferritin concentration and prognosis in carcinoma of the breast

Seven year follow-up data were available on 36 of 40 breast carcinoma patients in whom breast tissue ferritin concentrations at the time of surgery were known. 18 patients were alive and free of recurrence or second tumor (Group 1) and 11 died with breast cancer (Group 2). Patients with lower tissue ferritin concentrations defined as less than 319 ng/mcp (nanograms of ferritin/milligram of cytosol protein) were at reduced risk: 86% of patients with low tissue ferritin concentration survived free of recurrence or second tumor vs. 40% of patients with high tissue ferritin concentration (P = 0.0056). Mean breast carcinoma tissue ferritin concentration was 295 +/- 52 ng/mcp in Group 1 and 444 +/- 55 ng/mcp in Group 2 (P = 0.036). Lymph node involvement was predictive of mortality from breast carcinoma (P = 0.0003), but did not correlate with mean tissue ferritin concentration (P = 0.082). 10/10 (100%) patients who had both low tissue ferritin concentration and absence of lymph node involvement were in Group 1. The correlation of breast tissue ferritin concentration with histopathologic dedifferentiation and with prognosis suggests tumor tissue ferritin as a marker of malignant potential.

Characteristics of ferritins in human milk secretions: similarities to serum and tissue isoferritins

The ferritins present in the first day human colostrum and mature milk were compared with serum and tissue ferritins on the basis of their iron content, immunological reactivity and glycosylation. Both had a low iron content. The degree of glycosylation and immunochemical properties of colostrum ferritin showed strong similarities with serum ferritin. The isoelectric points and immunochemical properties of milk ferritin were similar to heart ferritin. The concentration of colostrum ferritin was more significantly correlated to body iron stores than milk ferritin.