Oxidized/deamidated-ceruloplasmin dysregulates choroid plexus epithelial cells functionality and barrier properties via RGD-recognizing integrin binding

Choroid plexus epithelial cells (CPEpiCs) determine the composition of cerebrospinal fluid (CSF) and constitute the blood-CSF barrier (BCSFB), functions that are altered in neurodegenerative diseases. In Parkinson's disease (PD) the pathological environment oxidizes and deamidates the ceruloplasmin, a CSF-resident ferroxidase, which undergoes a gain of RGD-recognizing integrin binding property, that may result in signal transduction. We investigated the effects that oxidized/deamidated ceruloplasmin (Cp-ox/de) may exert on CPEpiCs functions. Through RGD-recognizing integrins binding, Cp-ox/de mediates CPEpiCs adhesion and intracellular signaling, resulting in cell proliferation inhibition and alteration of the secretome profile in terms of proteins related to cell-extracellular matrix interaction. Oxidative conditions, comparable to those found in the CSF of PD patients, induced CPEpiCs barrier leakage, allowing Cp-ox/de to cross it, transducing integrins-mediated signal that further worsens BCSFB integrity. This mechanism might contribute to PD pathological processes altering CSF composition and aggravating the already compromised BCSFB function.

The Crossroads between Host Copper Metabolism and Influenza Infection

Three main approaches are used to combat severe viral respiratory infections. The first is preemptive vaccination that blocks infection. Weakened or dead viral particles, as well as genetic constructs carrying viral proteins or information about them, are used as an antigen. However, the viral genome is very evolutionary labile and changes continuously. Second, chemical agents are used during infection and inhibit the function of a number of viral proteins. However, these drugs lose their effectiveness because the virus can rapidly acquire resistance to them. The third is the search for points in the host metabolism the effect on which would suppress the replication of the virus but would not have a significant effect on the metabolism of the host. Here, we consider the possibility of using the copper metabolic system as a target to reduce the severity of influenza infection. This is facilitated by the fact that, in mammals, copper status can be rapidly reduced by silver nanoparticles and restored after their cancellation.

Thrombin inhibits the anti-myeloperoxidase and ferroxidase functions of ceruloplasmin: relevance in rheumatoid arthritis

Human ceruloplasmin (CP) is a multifunctional copper-binding protein produced in the liver. CP oxidizes Fe(2+) to Fe(3+), decreasing the concentration of Fe(2+) available for generating harmful oxidant species. CP is also a potent inhibitor of leukocyte myeloperoxidase (MPO) (Kd=130nM), a major source of oxidants in vivo. Rheumatoid arthritis (RA) is an inflammatory autoimmune disease affecting flexible joints and characterized by activation of both inflammatory and coagulation processes. Indeed, the levels of CP, MPO, and thrombin are markedly increased in the synovial fluid of RA patients. Here we show that thrombin cleaves CP in vitro at (481)Arg-Ser(482) and (887)Lys-Val(888) bonds, generating a nicked species that retains the native-like fold and the ferroxidase activity of the intact protein, whereas the MPO inhibitory function of CP is abrogated. Analysis of the synovial fluid of 24 RA patients reveals that CP is proteolytically degraded to a variable extent, with a fragmentation pattern similar to that observed with thrombin in vitro, and that proteolysis is blocked by hirudin, a highly potent and specific thrombin inhibitor. Using independent biophysical techniques, we show that thrombin has intrinsic affinity for CP (Kd=60-270nM), independent of proteolysis, and inhibits CP ferroxidase activity (KI=220±20nM). Mapping of thrombin binding sites with specific exosite-directed ligands (i.e., hirugen, fibrinogen γ'-peptide) and thrombin analogues having the exosites variably compromised (i.e., prothrombin, prethrombin-2, βT-thrombin) reveals that the positively charged exosite-II of thrombin binds to the negatively charged upper region of CP, while the protease active site and exosite-I remain accessible. These results suggest that thrombin can exacerbate inflammation in RA by impairing the MPO inhibitory function of CP via proteolysis and by competitively inhibiting CP ferroxidase activity. Notably, local administration of hirudin, a highly potent and specifc thrombin inhibitor, reduces the concentration of active MPO in the synovial fluid of RA patients and has a beneficial effect on the clinical symptoms of the disease.

Ceruloplasmin is an endogenous protectant against kainate neurotoxicity

To determine the role of ceruloplasmin (Cp) in epileptic seizures, we used a kainate (KA) seizure animal model and examined hippocampal samples from epileptic patients. Treatment with KA resulted in a time-dependent decrease in Cp protein expression in the hippocampus of rats. Cp-positive cells were colocalized with neurons or reactive astrocytes in KA-treated rats and epileptic patient samples. KA-induced seizures, initial oxidative stress (i.e., hydroxyl radical formation, lipid peroxidation, protein oxidation, and synaptosomal reactive oxygen species), altered iron status (increasing Fe(2+) accumulation and L-ferritin-positive reactive microglial cells and decreasing H-ferritin-positive neurons), and impaired glutathione homeostasis and neurodegeneration (i.e., Fluoro-Nissl and Fluoro-Jade B staining analyses) were more pronounced in Cp antisense oligonucleotide (ASO)- than in Cp sense oligonucleotide-treated rats. Consistently, Cp ASO facilitated KA-induced lactate dehydrogenase (LDH) release, Fe(2+) accumulation, and glutathione loss in neuron-rich and mixed cultures. However, Cp ASO did not alter KA-induced LDH release or Fe(2+) accumulation in the astroglial culture, but did facilitate impairment in glutathione homeostasis in the same culture. Importantly, treatment with human Cp protein resulted in a significant attenuation against these neurotoxicities induced by Cp ASO. Our results suggest that Cp-mediated neuroprotection occurs via the inhibition of seizure-associated oxidative damage (including impairment in glutathione homeostasis), Fe(2+) accumulation, and alterations in ferritin immunoreactivity. Moreover, interactive modulation between neurons and glia was found to be important for Cp upregulation in the attenuation of epileptic damage in both animals and humans.

[Roles of ceruloplasmin in silica-induced JNK/ERK/AP-1 cell signaling pathway change]

OBJECTIVE

To investigate the roles of ceruloplasmin (Cp) in JNK/ERK/ AP-1 cell signaling pathway change in human embryonic lung fibroblasts (HELFs) induced by silica.

METHODS

Cp stimulated HELFs in different time points (before 1 h, accompanied with or after 1 h of silica-adding). HELFs were divided into these groups: control group, silica(100 microg/ml for 24 h) group, Cp (30 microg/ml for 24 h) group and silica plus Cp (100 microg/ml silica plus 30 microg/ml Cp) group. DN-JNK cells and DN-ERK cells (cells were transfected with dominant negative mutant plasmid) contained these groups: control group, silica group, silica plus Cp group. MTT assay was used to detect the effects of Cp on silica-induced cell proliferation. Western blot assay was performed to detect the levels of JNK, ERK, c-Jun, c-Fos and their phosphorylated levels.

RESULTS

Cp promoted cell proliferation induced by silica when silica stimulated HELFs 1 h then adding to Cp. Cp significantly increased silica-induced the high levels of JNK, ERK and phosphorylated JNK (p-JNK), p-ERK, p-c-Jun and p-c-fos protein. After inhibition of JNK or ERK, silica-and-Cp-induced cell proliferation was markedly decreased. When suppressing JNK protein, the increased levels of p-JNK, p-c-Jun and p-c-fos protein was not observed. The high levels of p-ERK, p-c-Jun and p-c-fos protein were decreased when inhibiting ERK protein.

CONCLUSION

Cp could further strengthen silica-induced cell proliferation by JNK/c-Jun/c-Fos and ERK/c-Jun cell signaling pathway.

Mechanisms for cellular NO oxidation and nitrite formation in lung epithelial cells

Airway lining fluid contains relatively high concentrations of nitrite, and arterial blood levels of nitrite are higher than venous levels, suggesting the lung epithelium may represent an important source of nitrite in vivo. To investigate whether lung epithelial cells possess the ability to convert NO to nitrite by oxidation, and the effect of oxygen reactions on nitrite formation, the NO donor DETA NONOate was incubated with or without A549 cells or primary human bronchial epithelial (HBE) cells for 24 h under normoxic (21% O2) and hypoxic (1% O2) conditions. Nitrite production was significantly increased under all conditions in the presence of A549 or HBE cells, suggesting that both A549 and HBE cells have the capacity to oxidize NO to nitrite even under low-oxygen conditions. The addition of oxyhemoglobin to the A549 cell medium decreased the production of nitrite, consistent with NO scavenging limiting nitrite formation. Heat-denatured A549 cells produced much lower nitrite and nitrate, suggesting an enzymatic activity is required. This NO oxidation activity was highest in membrane-bound proteins with molecular size <100kDa. In addition, 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one and cyanide inhibited formation of nitrite in A549 cells. It has been shown that ceruloplasmin (Cp) possesses an NO oxidase and nitrite synthase activity in plasma based on NO oxidation to nitrosonium cation. We observed that Cp is expressed intracellularly in lung epithelial A549 cells and secreted into the medium under basal conditions and during cytokine stimulation. However, an analysis of Cp expression level and activity measured via p-phenylenediamine oxidase activity assay revealed very low activity compared with plasma, suggesting that there is insufficient Cp to contribute to detectable NO oxidation to nitrite in A549 cells. Additionally, Cp levels were knocked down using siRNA by more than 75% in A549 cells, with no significant change in either nitrite or cellular S-nitrosothiol formation compared to scrambled siRNA control under basal conditions or cytokine stimulation. These data suggest that lung epithelial cells possess NO oxidase activity, which is enhanced in cell-membrane-associated proteins and not regulated by intracellular or secreted Cp, indicating that alternative NO oxidases determine hypoxic and normoxic nitrite formation from NO in human lung epithelial cells.

Protective role of macrophage-derived ceruloplasmin in inflammatory bowel disease

OBJECTIVE

Intestinal microflora and inflammatory cell infiltrates play critical roles in the pathogenesis of acute colitis. Ceruloplasmin is an acute-phase plasma protein produced by hepatocytes and activated macrophages, and has ferroxidase with bactericidal activities. The goal is to understand the role of ceruloplasmin in colitis progression in a genetically modified murine model.

DESIGN

Experimental colitis was induced in ceruloplasmin null (Cp(-/-)) and wild-type (WT) mice by dextran sulphate sodium administration. The role of ceruloplasmin was further evaluated by transplantation of WT macrophages into Cp(-/-) mice.

RESULTS

Cp(-/-) mice rapidly lost weight and were moribund by day 14, while WT mice survived at least 30 days. Colon culture supernatants from Cp(-/-) mice exhibited elevated levels of TNFα, KC and MCP-1, indicative of increased inflammation and neutrophil and macrophage infiltration. Elevated leucocytes and severe histopathology were observed in Cp(-/-) mice. Elevated protein carbonyl content was detected in colons from Cp(-/-) mice suggesting ceruloplasmin antioxidant activity might contribute to its protective function. Unexpectedly, intraperitoneal administration of human ceruloplasmin into Cp(-/-) mice did not afford protection. Bone marrow transplantation from WT mice or injection of isolated peripheral blood monocytes markedly reduced severity of colitis and morbidity in Cp(-/-) mice.

CONCLUSION

Macrophage-derived ceruloplasmin contributes importantly to protection against inflammation and tissue injury in acute and chronic experimental colitis. The findings suggest that defects in ceruloplasmin expression or processing may influence the onset or progression of inflammatory bowel disease in patients.

Ceruloplasmin deficiency reduces levels of iron and BDNF in the cortex and striatum of young mice and increases their vulnerability to stroke

Ceruloplasmin (Cp) is an essential ferroxidase that plays important roles in cellular iron trafficking. Previous findings suggest that the proper regulation and subcellular localization of iron are very important in brain cell function and viability. Brain iron dyshomeostasis is observed during normal aging, as well as in several neurodegenerative disorders such as Alzheimer's, Parkinson's and Huntington's diseases, coincident with areas more susceptible to insults. Because of their high metabolic demand and electrical excitability, neurons are particularly vulnerable to ischemic injury and death. We therefore set out to look for abnormalities in the brain of young adult mice that lack Cp. We found that iron levels in the striatum and cerebral cortex of these young animals are significantly lower than wild-type (WT) controls. Also mRNA levels of the neurotrophin brain derived neurotrophic factor (BDNF), known for its role in maintenance of cell viability, were decreased in these brain areas. Chelator-mediated depletion of iron in cultured neural cells resulted in reduced BDNF expression by a posttranscriptional mechanism, suggesting a causal link between low brain iron levels and reduced BDNF expression. When the mice were subjected to middle cerebral artery occlusion, a model of focal ischemic stroke, we found increased brain damage in Cp-deficient mice compared to WT controls. Our data indicate that lack of Cp increases neuronal susceptibility to ischemic injury by a mechanism that may involve reduced levels of iron and BDNF.

[The role of ceruloplasmin in the differential diagnosis of neuropsychiatric disorders]

The blue copper protein ceruloplasmin has been of interest to psychiatrists for decades following Heilmeyer's observation of elevated serum copper levels in schizophrenic patients. Immunoturbidimetry, however, does not yield elevated serum ceruloplasmin concentrations in schizophrenia while ceruloplasmin-related oxidase activity appears to be elevated in patients with schizophrenia and reduced in patients with Alzheimer's disease. Low serum concentrations of immuno-turbidimetrically measured ceruloplasmin, and of oxidase activity, are typical of Wilson's disease, Menkes' disease, and aceruloplasminemia, three familial neurodegenerative disorders of pronounced variability, with regard to both genotype and phenotype. Especially patients with Wilson's disease may exhibit behavioural symptoms only over a long period. Heterozygous carriers of Wilson's disease and aceruloplasminaemia may have low serum ceruloplasmin concentrations; they will not develop somatic symptoms, but the significance of these carrier states, or of "hypoceruloplasminaemia", with regard to mental disorders is unknown.

A mouse mammary gland involution mRNA signature identifies biological pathways potentially associated with breast cancer metastasis

Mouse mammary gland involution resembles a wound healing response with suppressed inflammation. Wound healing and inflammation are also associated with tumour development, and a 'wound-healing' gene expression signature can predict metastasis formation and survival. Recent studies have shown that an involuting mammary gland stroma can promote metastasis. It could therefore be hypothesised that gene expression signatures from an involuting mouse mammary gland may provide new insights into the physiological pathways that promote breast cancer progression. Indeed, using the HOPACH clustering method, the human orthologues of genes that were differentially regulated at day 3 of mammary gland involution and showed prolonged expression throughout the first 4 days of involution distinguished breast cancers in the NKI 295 breast cancer dataset with low and high metastatic activity. Most strikingly, genes associated with copper ion homeostasis and with HIF-1 promoter binding sites were the most over-represented, linking this signature to hypoxia. Further, six out of the ten mRNAs with strongest up-regulation in cancers with poor survival code for secreted factors, identifying potential candidates that may be involved in stromal/matrix-enhanced metastasis formation/breast cancer development. This method therefore identified biological processes that occur during mammary gland involution, which may be critical in promoting breast cancer metastasis that could form a basis for future investigation, and supports a role for copper in breast cancer development.

A Multicopper Ferroxidase Involved in Iron Binding to Transferrins in Dunaliella salina Plasma Membranes

The halotolerant alga Dunaliella salina is unique among plants in that it utilizes a transferrin (TTf) to mediate iron acquisition (Fisher, M., Zamir, A., and Pick, U. (1998) J. Biol. Chem. 273, 17553-17558). Two new proteins that are induced by iron deprivation were identified in plasma membranes of D. salina as follows: a multicopper ferroxidase termed D-Fox and an internally duplicated glycoprotein (p130B). D-Fox and p130B are accessible to glycolytic, proteolytic, and biotin surface tagging treatments, suggesting that they are surface-exposed glycoproteins. Induction of D-Fox was also manifested by ferroxidase activity in plasma membrane preparations. These results are puzzling because ferroxidases in yeast and in Chlamydomonas reinhardtii function in redox-mediated iron uptake, a mechanism that is not known to operate in D. salina. Two lines of evidence suggest that D-Fox and p130B interact with D. salina triplicated transferrin (TTf). First, chemical cross-linking combined with mass spectroscopy analysis showed that D-Fox and p130B associate with TTf and with another plasma membrane transferrin. Second, detergent-solubilized D-Fox and p130B comigrated on blue native gels with plasma membrane transferrins. 59Fe autoradiography indicated that this complex binds Fe3+ ions. Also, the induction of D-Fox and p130B is kinetically correlated with enhanced iron binding and uptake activities. These results suggest that D-Fox and p130B associate with plasma membrane transferrins forming a complex that enhances iron binding and iron uptake. We propose that the function of D-Fox in D. salina has been modified during evolution from redox-mediated to transferrin-mediated iron uptake, following a gene transfer event of transferrins from an ancestral animal cell.

Ceruloplasmin expression and its role in iron transport in C6 cells

Ceruloplasmin (CP) is essential for brain iron homeostasis. However, little is known about the effect of iron on CP expression in the brain. Also, the role of CP in brain iron transport has not been well determined. In this study, we investigated the effects of iron on CP expression and the role of CP in iron transport in the C6 rat glioma cells. Our data showed that treatment of the cells with iron (cell iron overload) or iron chelators (cell iron deficiency) did not induce a significant change in the expression of CP mRNA. However, western blotting analysis demonstrated that cell iron overload induced a significant decrease in CP protein content in the cells and that treatment with iron chelators led to a significant increase in CP protein level in the cells. These findings suggest a translational regulation of CP expression by iron in the cells. We also examined the effects of CP on iron transport in the cells. We found that glycosylphosphatidylinositol-anchored CP did not have any impact on iron uptake by normal iron or iron-deficient cells nor on iron release from normal iron or iron-sufficient cells. However, low concentrations of soluble CP (2-8 microg/ml) increased iron uptake by iron-deficient C6 glioma cells, while the same concentrations of CP had no effect on iron uptake by normal iron cells and iron release from normal iron and iron-sufficient cells. The possible reason for the difference between our results in vitro and those obtained from in vivo studies was discussed.

Structure-function analysis of the cuprous oxidase activity in Fet3p from Saccharomyces cerevisiae

The Fet3 protein from Saccharomyces cerevisiae is a multicopper oxidase with specificity toward Fe(II) and Cu(I). Fet3p turnover of Fe(II) supports high affinity iron uptake across the yeast plasma membrane, whereas its turnover of Cu(I) contributes to copper resistance in yeast. The structure of Fet3p has been used to identify possible amino acid residues responsible for this protein's reactivity with Cu(I), and structure-function analyses have confirmed this assignment. Fet3p Met(345) is required for the enzyme's reactivity toward Cu(I). Although the Fet3pM345A mutant exhibits wild type spectral and electrochemical behavior, the kinetic constants for Cu(I) turnover and for single-turnover electron transfer from Cu(I) to the enzyme are significantly reduced. The specificity constant with Cu(I) as substrate is reduced by one-fifth, whereas the electron transfer rate from Cu(I) is reduced 50-fold. This mutation has little effect on the reactivity toward Fe(II), indicating that Met(345) contributes specifically to Fet3p reactivity with the cuprous ion. These kinetic defects render the Fet3pM345A unable to support wild type cellular copper resistance, suggesting that there is a finely tuned copper redox balance at the yeast plasma membrane.

Loss of vacuolar proton-translocating ATPase activity in yeast results in chronic oxidative stress

Yeast mutants lacking vacuolar proton-translocating ATPase (V-ATPase) subunits (vma mutants) were sensitive to several different oxidants in a recent genomic screen (Thorpe, G. W., Fong, C. S., Alic, N., Higgins, V. J., and Dawes, I. W. (2004) Proc. Natl. Acad. Sci. U. S. A. 101, 6564-6569). We confirmed that mutants lacking a V(1) subunit (vma2Delta), V(o) subunit, or either of the two V(o) a subunit isoforms are acutely sensitive to H(2)O(2) and more sensitive to menadione and diamide than wild-type cells. The vma2Delta mutant contains elevated levels of reactive oxygen species and high levels of oxidative protein damage even in the absence of an applied oxidant, suggesting an endogenous source of oxidative stress. vma2Delta mutants lacking mitochondrial DNA showed neither improved growth nor decreased sensitivity to peroxide, excluding respiration as the major source of the endogenous reactive oxygen species in the mutant. Double mutants lacking both VMA2 and components of the major cytosolic defense systems exhibited synthetic sensitivity to H(2)O(2). Microarray analysis comparing wild-type and vma2Delta mutant cells grown at pH 5, permissive conditions for the vma2Delta mutant, indicated high level up-regulation of several iron uptake and metabolism genes that are part of the Aft1/Aft2 regulon. TSA2, which encodes an isoform of the cytosolic thioredoxin peroxidase, was strongly induced, but other oxidative stress defense systems were not induced. The results indicate that V-ATPase activity helps to protect cells from endogenous oxidative stress.

Identification and biochemical properties of Dps (starvation-induced DNA binding protein) from cyanobacterium Anabaena sp. PCC 7120

DNA-binding Proteins from Starved cells (Dps) are anti-stress iron proteins preserving bacteria from oxidative damage. Based on sequence alignment, a 564-bp open reading frame (all1173) encoding product in Anabaena sp. PCC 7120 shared high similarity with Dps family proteins. RT-PCR showed all1173 is active at transcriptional level in Anabaena sp. PCC 7120 cells. We accordingly cloned the all1173 into prokaryotic expression system, purified the corresponding recombinant protein (Dps1173) and characterized its properties in vitro. According to CD spectrum and non-denaturing electrophoresis assays, recombinant Dps1173 was alpha helix riched, and was likely to form dodecametric oligomer under native conditions. Fluorescence titration experiment revealed two major iron binding sites within Dps1173 monomer, indicating its potential ferroxidase activity. Although phenomena of direct DNA binding was not observed in Electrophoretic mobility shift assay, Dps1173 could also protect DNA from H2O2 stress for its iron scavenging capacity. This is the first description of Dps from heterocystous cyanobacterium Anabaena sp. PCC 7120.

Lens epithelial cells synthesize and secrete ceruloplasmin: effects of ceruloplasmin and transferrin on iron efflux and intracellular iron dynamics

Although an essential nutrient, iron can catalyze damaging free radical reactions. Therefore elaborate mechanisms have evolved to carefully regulate iron metabolism. Ceruloplasmin, a protein with ferroxidase activity, and transferrin, an iron binding protein have important roles in maintaining iron homeostasis in cells. Since oxidative damage is a hallmark of cataractogenesis, it is essential to determine iron's role in lenticular physiology and pathology. In the current study of lens epithelial cells, the effects of ceruloplasmin and transferrin on intracellular distribution and efflux of iron were determined. Both ceruloplasmin and transferrin increased iron efflux from these cells and their effects were additive. Ceruloplasmin had significant effects on extracellular iron distribution only in cases of iron overload. Surprisingly, both transferrin and ceruloplasmin had significant effects on intracellular iron distribution. Under physiological conditions, ceruloplasmin increased iron incorporation into the storage protein, ferritin. Under conditions of iron overload, it decreased iron incorporation into ferritin, which is consistent with increased efflux of iron. Measurements of an intracellular chelatable iron pool indicated that both transferrin and ceruloplasmin increased the size of this pool at 24 h, but these increases had different downstream effects. Finally, lens epithelial cells made and secreted transferrin and ceruloplasmin. These results indicate an important role for these proteins in iron metabolism in the lens.

Translational control of ceruloplasmin gene expression: Beyond the IRE

Translational control is a common regulatory mechanism for the expression of iron-related proteins. For example, three enzymes involved in erythrocyte development are regulated by three different control mechanisms: globin synthesis is modulated by heme-regulated translational inhibitor, erythroid 5-aminolevulinate synthase translation is inhibited by binding of the iron regulatory protein to the iron response element in the 5'-untranslated region (UTR); and 15-lipoxygenase is regulated by specific proteins binding to the 3'-UTR. Ceruloplasmin (Cp) is a multi-functional, copper protein made primarily by the liver and by activated macrophages. Cp has important roles in iron homeostasis and in inflammation. Its role in iron metabolism was originally proposed because of its ferroxidase activity and because of its ability to stimulate iron loading into apo-transferrin and iron efflux from liver. We have shown that Cp mRNA is induced by interferon (IFN)-gamma in U937 monocytic cells, but synthesis of Cp protein is halted by translational silencing. The silencing mechanism requires binding of a cytosolic inhibitor complex, IFN-Gamma-Activated Inhibitor of Translation (GAIT), to a specific GAIT element in the Cp 3'-UTR. Here, we describe our studies that define and characterize the GAIT element and elucidate the specific trans-acting proteins that bind the GAIT element. Our experiments describe a new mechanism of translational control of an iron-related protein and may shed light on the role that macrophage-derived Cp plays at the intersection of iron homeostasis and inflammation.

Ceruloplasmin in neurodegenerative diseases

For decades, abnormalities in ceruloplasmin (Cp) synthesis have been associated with neurodegenerative disease. From the early observation that low circulating serum ceruloplasmin levels served as a marker for Wilson's disease to the recent characterization of a neurodegenerative disorder associated with a complete lack of serum ceruloplasmin, the link between Cp and neuropathology has strengthened. The mechanisms associated with these different central nervous system abnormalities are very distinct. In Wilson's disease, a defect in the P-type ATPase results in abnormal hepatic copper accumulation that eventually leaks into the circulation and is abnormally deposited in the brain. In this case, copper deposition results in the neurodegenerative phenotype observed. Patients with autosomal recessive condition, aceruloplasminemia, lack the ferroxidase activity inherent to the multi-copper oxidase ceruloplasmin and develop abnormal iron accumulation within the central nervous system. In the following review ceruloplasmin gene expression, structure and function will be presented and the role of ceruloplasmin in iron metabolism will be discussed. The molecular events underlying the different forms of neurodegeneration observed will be presented. Understanding the role of ceruloplasmin within the central nervous system is fundamental to further our understanding of the pathology observed. Is the ferroxidase function more essential than the antioxidant role? Does Cp help maintain nitrosothiol stores or does it oxidize critical brain substrates? The answers to these questions hold the promise for the treatment of devastating neurodegenerative conditions such as Alzheimer's and Parkinson's diseases. It is essential to further elucidate the mechanism of the neuronal injury associated with these disorders.

The copper-iron connection in biology: structure of the metallo-oxidase Fet3p

Fet3p is a multicopper-containing glycoprotein localized to the yeast plasma membrane that catalyzes the oxidation of Fe(II) to Fe(III). This ferrous iron oxidation is coupled to the reduction of O(2) to H(2)O and is termed the ferroxidase reaction. Fet3p-produced Fe(III) is transferred to the permease Ftr1p for import into the cytosol. The posttranslational insertion of four copper ions into Fet3p is essential for its activity, thus linking copper and iron homeostasis. The mammalian ferroxidases ceruloplasmin and hephaestin are homologs of Fet3p. Loss of the Fe(II) oxidation catalyzed by these proteins results in a spectrum of pathological states, including death. Here, we present the structure of the Fet3p extracellular ferroxidase domain and compare it with that of human ceruloplasmin and other multicopper oxidases that are devoid of ferroxidase activity. The Fet3p structure delineates features that underlie the unique reactivity of this and homologous multicopper oxidases that support the essential trafficking of iron in diverse eukaryotic organisms. The findings are correlated with biochemical and physiological data to cross-validate the elements of Fet3p that define it as both a ferroxidase and cuprous oxidase.

Inflammation-sensitive proteins and erythrocyte aggregation in atherothrombosis

OBJECTIVE

To find the relative contribution of various inflammation-sensitive proteins including fibrinogen, immunoglobulins (IgG, IgM and IgA), ceruloplasmin and high sensitivity C-reactive protein (hs-CRP) to the induction and/or maintenance of enhanced erythrocyte adhesiveness/aggregation in the peripheral blood of individuals with atherothrombotic risk factors.

METHODS

The degree of erythrocyte adhesiveness/aggregation was determined by a simple slide test and image analysis. In addition, we measured various inflammation-sensitive protein levels including fibrinogen, ceruloplasmin, immunoglobulins and hs-CRP in a group of 234 individuals with atherothrombotic risk factors and healthy ones. Pearson partial correlations and multiple linear regression analysis were performed.

RESULTS

Fibrinogen was found to be the major protein contributing to the enhanced erythrocyte adhesiveness/aggregation, explaining 30% of the model. Fibrinogen and IgG together explained 32.4% of the model. Other inflammation-sensitive proteins did not reach statistical significance and were excluded from the model.

CONCLUSIONS

Among inflammation-sensitive proteins measured in our cohort, fibrinogen is the dominant contributor to erythrocyte adhesiveness/aggregation in the peripheral blood of individuals with atherothrombotic risk factors and healthy ones. These findings may pave the way for the development of therapeutic strategies directed at the attenuation of erythrocyte aggregability in individuals with atherothrombosis.

[The role of ceruloplasmin in neoplastic processes]

Ceruloplasmin (CP) is a copper containing oxidase of human plasma alpha 2-globulin fraction. The review summarizes literature data on biological role of CP under normal conditions and during development of malignant tumor. This protein may be involved both into antitumor deference and also into metastasizing process. Although CP has already been employed into intensive therapy of oncologic patients all mechanisms underlying its biological activity remain to be clarified.

Iron and ageing: an introduction to iron regulatory mechanisms

While there have been significant advances made in our understanding of the cellular and molecular mechanisms that regulate iron absorption, transport, storage, and utilization, the effect of ageing on these mechanisms and the role of iron in the ageing process is not fully understood. Thus, this review will provide an overview of the iron regulatory mechanisms that may be a factor in the ageing process. Additional reviews in this volume represent an attempt to explore the very latest information on the regulation of iron with a particular emphasis on age-related pathology including mitochondrial function, Parkinson's disease, Alzheimer's disease, stroke, and cardiovascular disease.

The blue copper ceruloplasmin induces aggregation of newly differentiated neurons: a potential modulator of nervous system organization

Ceruloplasmin (CP) is a copper-dependent ferroxidase. It regulates iron metabolism and is involved in inflammation, angiogenesis, and protection against oxidative stress. CP also modulates K(+) channel activity in neuroblastoma cells and affects cardiodynamics of isolated hearts. Considering the presence of CP in the nervous system and the importance of iron ions and K(+) channels in neuronal activity, we postulated a role of CP in neuronal development. This hypothesis was tested using the P19 mouse embryonal carcinoma cell line, a model of neuronal differentiation. Addition of CP to the culture medium of newly differentiated P19 neurons induced cell aggregation within 24 h. This effect was concentration-dependent half-maximal at 50 nM, and not associated with necrosis, apoptosis or changes in secretory function. Deglycosylated CP was aggregative but not denatured CP, copper salts, His(2)Cu complex, or other copper enzymes or serum proteins. CP-induced aggregation was less pronounced with aging neurons and seemed not to involve K(+) channels. Immunocytofluorescence analysis demonstrated that digoxigenin-labeled CP bound to P19 neurons and the proportion of responding neurons decreased with aging. The interaction of digoxigenin-labeled CP with neurons was half-maximal at 120 nM by enzyme-linked immunosorbent assay and displaced by unlabeled CP. Our data indicate a specific aggregative action of CP on young neurons in vitro, possibly involving CP receptors. A potential developmental role of CP in nervous system organization is thus demonstrated.

Role of ceruloplasmin in macrophage iron efflux during hypoxia

The reticuloendothelial system has a central role in erythropoiesis and iron homeostasis. An important function of reticuloendothelial macrophages is phagocytosis of senescent red blood cells. The iron liberated from heme is recycled for delivery to erythrocyte precursors for a new round of hemoglobin synthesis. The molecular mechanism by which recycled iron is released from macrophages remains unresolved. We have investigated the mechanism of macrophage iron efflux, focusing on the role of ceruloplasmin (Cp), a copper protein with a potent ferroxidase activity that converts Fe2+ to Fe3+ in the presence of molecular oxygen. As shown by others, Cp markedly increased iron binding to apotransferrin at acidic pH; however, the physiological significance of this finding is uncertain because little stimulation was observed at neutral pH. Introduction of a hypoxic atmosphere resulted in marked Cp-stimulated binding of iron to apotransferrin at physiological pH. The role of Cp in cellular iron release was examined in U937 monocytic cells induced to differentiate to the macrophage lineage. Cp added at its normal plasma concentration increased the rate of 55Fe release from U937 cells by about 250%. The stimulation was absolutely dependent on the presence of apotransferrin and hypoxia. Cp-stimulated iron release was confirmed in mouse peritoneal macrophages. Stimulation of iron release required an intracellular "labile iron pool" that was rapidly depleted in the presence of Cp and apotransferrin. Ferroxidase-mediated loading of iron into apotransferrin was critical for iron release because ferroxidase-deficient Cp was inactive and because holotransferrin could not substitute for apotransferrin. The extracellular iron concentration was critical as shown by inhibition of iron release by exogenous free iron, and marked enhancement of release by an iron chelator. Together these data show that Cp stimulates iron release from macrophages under hypoxic conditions by a ferroxidase-dependent mechanism, possibly involving generation of a negative iron gradient.

Molecular basis of H2O2 resistance mediated by Streptococcal Dpr. Demonstration of the functional involvement of the putative ferroxidase center by site-directed mutagenesis in Streptococcus suis

H(2)O(2) is an unavoidable cytotoxic by-product of aerobic life. Dpr, a recently discovered member of the Dps protein family, provides a means for catalase-negative bacteria to tolerate H(2)O(2). Potentially, Dpr could bind free intracellular iron and thus inhibit the Fenton chemistry-catalyzed formation of toxic hydroxyl radicals (H(2)O(2) + Fe(2+) --> (.)OH + (-)OH + Fe(3+)). We explored the in vivo function of Dpr in the catalase- and NADH peroxidase-negative pig and human pathogen Streptococcus suis. We show that: (i) a Dpr allelic exchange knockout mutant was hypersensitive ( approximately 10(6)-fold) to H(2)O(2), (ii) Dpr incorporated iron in vivo, (iii) a putative ferroxidase center was present in Dpr, (iv) single amino acid substitutions D74A or E78A to the putative ferroxidase center abolished the in vivo iron incorporation, and (v) the H(2)O(2) hypersensitive phenotype was complemented by wild-type Dpr or by a membrane-permeating iron chelator, but not by the site-mutated forms of Dpr. These results demonstrate that the putative ferroxidase center of Dpr is functionally active in iron incorporation and that the H(2)O(2) resistance is mediated by Dpr in vivo by its iron binding activity.

Ceruloplasmin metabolism and function

Ceruloplasmin is a serum ferroxidase that contains greater than 95% of the copper found in plasma. This protein is a member of the multicopper oxidase family, an evolutionarily conserved group of proteins that utilize copper to couple substrate oxidation with the four-electron reduction of oxygen to water. Despite the need for copper in ceruloplasmin function, this protein plays no essential role in the transport or metabolism of this metal. Aceruloplasminemia is a neurodegenerative disease resulting from inherited loss-of-function mutations in the ceruloplasmin gene. Characterization of this disorder revealed a critical physiological role for ceruloplasmin in determining the rate of iron efflux from cells with mobilizable iron stores and has provided new insights into human iron metabolism and nutrition.

The copper-iron connection: hereditary aceruloplasminemia

Hereditary aceruloplasminemia is an autosomal recessive disorder of iron homeostasis due to loss-of-function mutations in the ceruloplasmin gene. Affected individuals may present in adulthood with evidence of hepatic iron overload, diabetes, peripheral retinal degeneration, dystonia, dementia, or dysarthria. Laboratory studies demonstrate microcytic anemia, elevated serum ferritin, and a complete absence of serum ceruloplasmin ferroxidase activity. Consistent with the observed neurologic findings, magnetic resonance imaging reveals iron accumulation within the basal ganglia. Histologic studies detect abundant iron in hepatocytes, reticuloendothelial cells of the liver and spleen, beta cells of the pancreas, and astrocytes and neurons throughout the central nervous system. Characterization of this disorder reveals an essential role for ceruloplasmin in determining the rate of iron efflux from cells with mobilizable iron stores and provides new insights into the mechanisms of human iron metabolism.

[Effects of low intensity laser (632.8 nm) and ultraviolet radiation on spectral properties and functional activity of human ceruloplasmin]

Photoinduced changes of human ceruloplasmin (hCp) under laser and ultraviolet (UV) radiation have been studied. A complex character of hCp spectral modifications points to a different degree of the protein molecule folding. After the influence of UV radiation (240-390 nm) in a dose range 906-4530 J/m2 the decrease of oxidase hCp activity was registered. These changes are thought to be connected with modification of the conformation of hCp active centre or copper reduction that was confirmed by the decrease of optical density at 610 nm. An inactivation constant (kf = 3.8 x 10(-4) 1/s) and a photoinactivation quantum yield (1.4 x 10(-4)) were calculated. Kinetic dependencies of o-phenilen-diamine oxidation by intact and UV-modified glycoprotein do not correspond to Michaelis-Menten equation. UV radiation in a dose range 151-4530 J/m2 induced increasing of ceruloplasmin superoxiddismutase activity. The influence of He-Ne laser radiation (1.3 mW; lambda = 632.8 nm, exposure time from 1 up to 30 min) leads to the raise of the hCp functional activity; superoxiddismutase activity changes more significantly. Possible photophysical and photochemical processes in hCp molecule, leading to photomodification and changes of protein functional activity have been represented on the scheme.

Relative roles of albumin and ceruloplasmin in the formation of homocystine, homocysteine-cysteine-mixed disulfide, and cystine in circulation

Disulfide forms of homocysteine account for >98% of total homocysteine in plasma from healthy individuals. We recently reported that homocysteine reacts with albumin-Cys(34)-S-S-cysteine to form homocysteine-cysteine mixed disulfide and albumin-Cys(34) thiolate anion. The latter then reacts with homocystine or homocysteine-cysteine mixed disulfide to form albumin-bound homocysteine (Sengupta, S., Chen, H., Togawa, T., DiBello, P. M., Majors, A. K., Büdy, B., Ketterer, M. E., and Jacobsen, D. W. (2001) J. Biol. Chem. 276, 30111-30117). We now extend these studies to show that human albumin, but not ceruloplasmin, mediates the conversion of homocysteine to its low molecular weight disulfide forms (homocystine and homocysteine-cysteine mixed disulfide) by thiol/disulfide exchange reactions. Only a small fraction of homocystine is formed by an oxidative process in which copper bound to albumin, but not ceruloplasmin, mediates the reaction. When copper is removed from albumin by chelation, the overall conversion of homocysteine to its disulfide forms is reduced by only 20%. Ceruloplasmin was an ineffective catalyst of homocysteine oxidation, and immunoprecipitation of ceruloplasmin from human plasma did not inhibit the capacity of plasma to mediate the conversion of homocysteine to its disulfide forms. In contrast, ceruloplasmin was a highly efficient catalyst for the oxidation of cysteine and cysteinylglycine to cystine and bis(-S-cysteinylglycine), respectively. However, when thiols (cysteine and homocysteine) that are disulfide-bonded to albumin-Cys(34) are removed by treatment with dithiothreitol to form albumin-Cys(34)-SH (mercaptalbumin), the conversion of homocysteine to its disulfide forms is completely blocked. In conclusion, albumin mediates the formation of disulfide forms of homocysteine by thiol/disulfide exchange, whereas ceruloplasmin converts cysteine to cystine by copper-dependent autooxidation.

Copper transport and metabolism are normal in aceruloplasminemic mice

Ceruloplasmin is an abundant serum glycoprotein containing greater than 95% of the copper found in the plasma of vertebrate species. Although this protein is known to function as an essential ferroxidase, the role of ceruloplasmin in copper transport and metabolism remains unclear. To elucidate the role of ceruloplasmin in copper metabolism, the kinetics of copper absorption, transport, distribution, and excretion were examined utilizing (64)Cu in wild-type and aceruloplasminemic mice. No differences in gastrointestinal absorption, hepatic uptake, or biliary excretion were observed in these animals. Furthermore, steady state measurements of tissue copper content utilizing (64)Cu and atomic absorption spectroscopy revealed no differences in the copper content of the brain, heart, spleen, and kidney. Consistent with these findings, the activity of copper-zinc superoxide dismutase in these tissues was equivalent in wild-type and ceruloplasmin-deficient mice. Hepatic iron was elevated 3.5-fold in aceruloplasminemic mice because of the loss of ferroxidase function. Hepatic copper content was markedly increased in aceruloplasminemic mice. As no differences were observed in copper absorption or biliary copper excretion, these data suggest that in these animals, hepatocyte copper intended for ceruloplasmin incorporation is trafficked into a compartment that is less available for biliary copper excretion. Taken together, these data reveal no essential role for ceruloplasmin in copper metabolism and suggest a previously unappreciated complexity to the subcellular distribution of this metal within the hepatocyte secretory pathway.

Cellular copper transport and metabolism

The transport and cellular metabolism of Cu depends on a series of membrane proteins and smaller soluble peptides that comprise a functionally integrated system for maintaining cellular Cu homeostasis. Inward transport across the plasma membrane appears to be a function of integral membrane proteins that form the channels that select Cu ions for passage. Two membrane-bound Cu-transporting ATPase enzymes, ATP7A and ATP7B, the products of the Menkes and Wilson disease genes, respectively, catalyze an ATP-dependent transfer of Cu to intracellular compartments or expel Cu from the cell. ATP7A and ATP7B work in concert with a series of smaller peptides, the copper chaperones, that exchange Cu at the ATPase sites or incorporate the Cu directly into the structure of Cu-dependent enzymes such as cytochrome c oxidase and Cu, Zn superoxide dismutase. These mechanisms come into play in response to a high influx of Cu or during the course of normal Cu metabolism.

The physiopathological significance of ceruloplasmin. A possible therapeutic approach

This article reviews and comments on the physiological roles of ceruloplasmin (Cp). We show that, in addition to its ascertained involvement in iron homeostasis, the protein, by virtue of its unique structure among multicopper oxidases, is likely involved in other processes of both an enzymatic and a nonenzymatic nature. In particular, based on the analysis of the kinetic parameters, on the one hand, and of the side-products of the oxidation, on the other, we propose that the long-recognized ability of Cp to interact with and oxidize non-iron substrates may be of physiological relevance. The striking example of 6-hydroxydopamine oxidation is presented, where we show that the catalytic action is carried out readily under physiological conditions, without release of potentially toxic oxygen intermediates.

Biological functions of ceruloplasmin and their deficiency caused by mutation in genes regulating copper and iron metabolism

Ceruloplasmin, a multicopper ferroxidase, is involved in iron and copper homeostasis and integrates these metabolic pathways. Impaired biosynthesis of ceruloplasmin caused by gene mutations disturbs iron metabolism with iron deposition in different organs, especially in the basal ganglia, and severe neuronal damage. Dysfunction of ATP7B, a copper-transporting ATPase leads to the development of Wilson's disease, i.e., multiple abnormalities in copper metabolism associated with reduced synthesis of holoceruloplasmin and biliary copper excretion controlled by both proteins. The lowest content of serum ceruloplasmin is observed in the most grave early neurological form of Wilson's disease (according to N. V. Konovalov's classification), which confirms the important role of ceruloplasmin in the striatal metabolism of catecholamines.

Targeted gene disruption reveals an essential role for ceruloplasmin in cellular iron efflux

Aceruloplasminemia is an autosomal recessive disorder of iron metabolism. Affected individuals evidence iron accumulation in tissue parenchyma in association with absent serum ceruloplasmin. Genetic studies of such patients reveal inherited mutations in the ceruloplasmin gene. To elucidate the role of ceruloplasmin in iron homeostasis, we created an animal model of aceruloplasminemia by disrupting the murine ceruloplasmin (Cp) gene. Although normal at birth, Cp(-/-) mice demonstrate progressive accumulation of iron such that by one year of age all animals have a prominent elevation in serum ferritin and a 3- to 6-fold increase in the iron content of the liver and spleen. Histological analysis of affected tissues in these mice shows abundant iron stores within reticuloendothelial cells and hepatocytes. Ferrokinetic studies in Cp(+/+) and Cp(-/-) mice reveal equivalent rates of iron absorption and plasma iron turnover, suggesting that iron accumulation results from altered compartmentalization within the iron cycle. Consistent with this concept, Cp(-/-) mice showed no abnormalities in cellular iron uptake but a striking impairment in the movement of iron out of reticuloendothelial cells and hepatocytes. Our findings reveal an essential physiologic role for ceruloplasmin in determining the rate of iron efflux from cells with mobilizable iron stores.

The role of copper in neurodegenerative disease

Copper is an essential trace metal which plays a fundamental role in the biochemistry of the human nervous system. Menkes disease and Wilson disease are inherited disorders of copper metabolism and the dramatic neurodegenerative phenotypes of these two diseases underscore the essential nature of copper in nervous system development as well as the toxicity of this metal when neuronal copper homeostasis is perturbed. Ceruloplasmin contains 95% of the copper found in human plasma and inherited loss of this essential ferroxidase is associated with progressive neurodegeneration of the retina and basal ganglia. Gain-of-function mutations in the cytosolic copper enzyme superoxide dismutase result in the motor neuron degeneration of amyotrophic lateral sclerosis and current evidence suggests a direct pathogenic role for copper in this process. Recent studies have also implicated copper in the pathogenesis of neuronal injury in Alzheimer's disease and the prion-mediated encephalopathies, suggesting that further elucidation of the mechanisms of copper trafficking and metabolism within the nervous system will be of direct relevance to our understanding of the pathophysiology and treatment of neurodegenerative disease.

Defective antioxidant mechanisms via changes in serum ceruloplasmin and total iron binding capacity of serum in women with pre-eclampsia

OBJECTIVES

The aim of this study was to investigate the role of serum ceruloplasmin, its ferroxidase activity and total iron binding capacity in women with pre-eclampsia.

METHODS

Thirty primigravidas between 32 and 36 weeks of gestation were studied. The subjects were divided into two groups: group A consisted of 15 normal pregnancies with a mean gestational age of 33.9 weeks, and group B consisted of 15 pre-eclamptics with a mean gestational age of 32.8 weeks.

RESULTS

The pre-eclamptics presented significantly higher serum ceruloplasmin levels compared to those with normal pregnancies (P<0.01), while the mean ferroxidase activity levels of ceruloplasmin did not differ significantly between the two groups (450.13+/-110.88 and 467.26+/-135.35 micromol/l/min in groups A and B, respectively). The mean+/-S.D. serum iron level (104.48+/-39.81 microg/dl) was greater whereas the total iron binding capacity (55.59+/-8.47 micromol/l) was lower in women with preeclampsia when compared to normal pregnancies (P<0.01 and P<0.0001 respectively).

CONCLUSIONS

Our results indicate that the plasma of pre-eclamptic women shows a loss of ferroxidase activity of ceruloplasmin as well as a reduction of total iron binding capacity. Thus, it seems that the plasma of pre-eclamptic women lacks the protective anti-oxidative action of these substances.

Requirement of intact human ceruloplasmin for the glutathione-linked peroxidase activity

Structural integrity may be needed for the glutathione-linked peroxidase activity of human ceruloplasmin. Intact human ceruloplasmin has a potent peroxidase property to decompose H2O2 in the presence of reduced glutathione. However, the fragment of approximately 116000 Da produced by proteolytic degradation had less than one-third of the glutathione-linked peroxidase activity of intact ceruloplasmin. When further proteolysis occurred, glutathione-linked peroxidase activity of human ceruloplasmin disappeared. In contrast, ceruloplasmin (116000 Da and <96000 Da) fragmented by proteolysis significantly removed H2O2 irrespective of the presence of reduced glutathione. Although proteolytic fragmentation of ceruloplasmin occurs, the antioxidant activity of ceruloplasmin that prevents DNA strand breaks in a metal-catalyzed reaction system was significantly maintained.

Aceruloplasminemia: an inherited neurodegenerative disease with impairment of iron homeostasis

Aceruloplasminemia is an autosomal recessive disorder characterized by progressive neurodegeneration of the retina and basal ganglia associated with specific inherited mutations in the ceruloplasmin gene. Clinical and pathologic studies in patients with aceruloplasminemia revealed a marked accumulation of iron in affected parenchymal tissues, a finding consistent with early work identifying ceruloplasmin as a ferroxidase and with recent findings showing an essential role for a homologous copper oxidase in iron metabolism in yeast. The presence of neurologic symptoms in aceruloplasminemia is unique among the known inherited and acquired disorders of iron metabolism; recent studies revealed an essential role for astrocyte-specific expression of ceruloplasmin in iron metabolism and neuronal survival in the central nervous system. Recognition of aceruloplasminemia provides new insights into the genetic and environmental determinants of copper metabolism and has important implications for our understanding of the role of copper in human neurodegenerative diseases.

Copper transport

In adult humans, the net absorption of dietary copper is approximately 1 mg/d. Dietary copper joins some 4-5 mg of endogenous copper flowing into the gastrointestinal tract through various digestive juices. Most of this copper returns to the circulation and to the tissues (including liver) that formed them. Much lower amounts of copper flow into and out of other major parts of the body (including heart, skeletal muscle, and brain). Newly absorbed copper is transported to body tissues in two phases, borne primarily by plasma protein carriers (albumin, transcuprein, and ceruloplasmin). In the first phase, copper goes from the intestine to the liver and kidney; in the second phase, copper usually goes from the liver (and perhaps also the kidney) to other organs. Ceruloplasmin plays a role in this second phase. Alternatively, liver copper can also exit via the bile, and in a form that is less easily reabsorbed. Copper is also present in and transported by other body fluids, including those bathing the brain and central nervous system and surrounding the fetus in the amniotic sac. Ceruloplasmin is present in these fluids and may also be involved in copper transport there. The concentrations of copper and ceruloplasmin in milk vary with lactational stage. Parallel changes occur in ceruloplasmin messenger RNA expression in the mammary gland (as determined in pigs). Copper in milk ceruloplasmin appears to be particularly available for absorption, at least in rats.

The protective role of ceruloplasmin against the activity of free radicals in brain ischaemia

Free radicals are atoms, groups of atoms or particles having on their last orbital at least one unpaired electron. This feature decides about their great chemical reactivity and lability (12, 16). To potentially toxic oxygen radicals belong: peroxidal anion radical, hydroxidal radical, hydrogen peroxide, hydroxylic radical, peroxidal lipid radical, singletal oxygen (12). The presence of free radicals in biological systems may play a role in etiopathogenesis of different illnesses. Overactivity of these compounds causes damage of tissues and bodily organs (3, 16, 18).

Role of ceruloplasmin in cellular iron uptake

Individuals with hereditary ceruloplasmin (Cp) deficiency have profound iron accumulation in most tissues, which suggests that Cp is important for normal release of cellular iron. Here, in contrast to expectations, Cp was shown to increase iron uptake by HepG2 cells, increasing the apparent affinity for the substrate by three times. Consistent with its role in iron uptake, Cp synthesis was regulated by iron supply and was increased four- to fivefold after iron depletion. Unlike other iron controllers that are posttranscriptionally regulated, Cp synthesis was transcriptionally regulated. Thus, iron-deficient cells could increase Cp synthesis to maintain intracellular iron homeostasis, so that defects would lead to global accumulation of iron in tissues.