Coordinate transcriptional and translational regulation of ferritin in response to oxidative stress

Oxidative Stress and ADHD: A Meta-Analysis

OBJECTIVE

To clarify the role of oxidative stress and antioxidant activity in ADHD.

METHOD

We examined the association of ADHD and oxidative stress by applying random effects meta-analysis to studies of oxidative stress and antioxidant status in medication naive patients with ADHD and controls.

RESULTS

Six studies of a total of 231 ADHD patients and 207 controls met our selection criteria. The association between ADHD and antioxidant status was not significant. We found a significant association between ADHD and oxidative stress that could not be accounted for by publication bias. The significant association lost significance after correcting for intrastudy clustering. No one observation accounted for the positive result.

CONCLUSION

These results are preliminary given the small number of studies. They suggest that patients with ADHD have normal levels of antioxidant production, but that their response to oxidative stress is insufficient, leading to oxidative damage.

Cytoprotective Effect of Ferritin H in Renal Ischemia Reperfusion Injury

Oxidative stress is a major contributor to kidney injury following ischemia reperfusion. Ferritin, a highly conserved iron-binding protein, is a key protein in the maintenance of cellular iron homeostasis and protection from oxidative stress. Ferritin mitigates oxidant stress by sequestering iron and preventing its participation in reactions that generate reactive oxygen species. Ferritin is composed of two subunit types, ferritin H and ferritin L. Using an in vivo model that enables conditional tissue-specific doxycycline-inducible expression of ferritin H in the mouse kidney, we tested the hypothesis that an increased level of H-rich ferritin is renoprotective in ischemic acute renal failure. Prior to induction of ischemia, doxycycline increased ferritin H in the kidneys of the transgenic mice nearly 6.5-fold. Following reperfusion for 24 hours, induction of neutrophil gelatinous-associated lipocalin (NGAL, a urine marker of renal dysfunction) was reduced in the ferritin H overexpressers compared to controls. Histopathologic examination following ischemia reperfusion revealed that ferritin H overexpression increased intact nuclei in renal tubules, reduced the frequency of tubular profiles with luminal cast materials, and reduced activated caspase-3 in the kidney. In addition, generation of 4-hydroxy 2-nonenal protein adducts, a measurement of oxidant stress, was decreased in ischemia-reperfused kidneys of ferritin H overexpressers. These studies demonstrate that ferritin H can inhibit apoptotic cell death, enhance tubular epithelial viability, and preserve renal function by limiting oxidative stress following ischemia reperfusion injury.

Exposure to toxic Alexandrium minutum activates the detoxifying and antioxidant systems in gills of the oyster Crassostrea gigas

Harmful algal blooms of Alexandrium spp. dinoflagellates regularly occur in French coastal waters contaminating shellfish. Studies have demonstrated that toxic Alexandrium spp. disrupt behavioural and physiological processes in marine filter-feeders, but molecular modifications triggered by phycotoxins are less well understood. This study analyzed the mRNA levels of 7 genes encoding antioxidant/detoxifying enzymes in gills of Pacific oysters (Crassostrea gigas) exposed to a cultured, toxic strain of A. minutum, a producer of paralytic shellfish toxins (PST) or fed Tisochrysis lutea (T. lutea, formerly Isochrysis sp., clone Tahitian (T. iso)), a non-toxic control diet, in four repeated experiments. Transcript levels of sigma-class glutathione S-transferase (GST), glutathione reductase (GR) and ferritin (Fer) were significantly higher in oysters exposed to A. minutum compared to oysters fed T. lutea. The detoxification pathway based upon glutathione (GSH)-conjugation of toxic compounds (phase II) is likely activated, and catalyzed by GST. This system appeared to be activated in gills probably for the detoxification of PST and/or extra-cellular compounds, produced by A. minutum. GST, GR and Fer can also contribute to antioxidant functions to prevent cellular damage from increased reactive oxygen species (ROS) originating either from A. minutum cells directly, from oyster hemocytes during immune response, or from other gill cells as by-products of detoxification.

Role of extracellular Hydrogen peroxide in regulation of iron homeostasis genes in neuronal cells: Implication in iron accumulation

Iron accumulation and oxidative stress are associated with neurodegenerative disease. Labile iron is known to catalyze free radical generation and subsequent neuronal damage, whereas the role of oxidative stress in neuronal iron accumulation is less well understood. Here, we examined the effect of hydrogen peroxide (H2O2) treatment on cellular iron-uptake, -storage, and -release proteins in the neuroblastoma cell line SH-SY5Y. We found no detectable change in the iron-uptake proteins transferrin receptor-1 and divalent metal ion transporter. In contrast, H2O2 treatment resulted in significant degradation of the iron-exporter ferroportin (Fpn). A decrease in Fpn is expected to increase the labile iron pool (LIP), reducing the iron-regulatory protein (IRP)-iron-responsive element interaction and increasing the expression of ferritin-H (Ft-H) for iron storage. Instead, we detected IRP1 activation, presumably due to oxidative stress, and a decrease in Ft-H translation. A reduction in Ft-H mRNA was also observed, probably dependent on an antioxidant-response element present in the Ft-H enhancer. The decrease in Fpn and Ft-H upon H2O2 treatment led to a time-dependent increase in the cellular LIP. Our study reveals a complex regulation of neuronal iron-release and iron-storage components in response to H2O2 that may explain iron accumulation detected in neurodegenerative diseases associated with oxidative stress.

Oxidative stress and the homeodynamics of iron metabolism

Iron and oxygen share a delicate partnership since both are indispensable for survival, but if the partnership becomes inadequate, this may rapidly terminate life. Virtually all cell components are directly or indirectly affected by cellular iron metabolism, which represents a complex, redox-based machinery that is controlled by, and essential to, metabolic requirements. Under conditions of increased oxidative stress—i.e., enhanced formation of reactive oxygen species (ROS)—however, this machinery may turn into a potential threat, the continued requirement for iron promoting adverse reactions such as the iron/H2O2-based formation of hydroxyl radicals, which exacerbate the initial pro-oxidant condition. This review will discuss the multifaceted homeodynamics of cellular iron management under normal conditions as well as in the context of oxidative stress.

Serum ferritin levels predict histological severity in patients with nonalcoholic fatty liver disease in India

AIM

The aims of the study were to determine the levels of serum ferritin which predict fibrosis in Indian patients with nonalcoholic fatty liver disease (NAFLD) and to establish correlation between Fibroscan values and serum ferritin levels.

METHODS

The clinical, biochemical, radiologic, and histological findings of consecutive adult NAFLD patients accessed at a tertiary care center over a 3-year period were analyzed. Those with concurrent liver diseases were excluded. Fifty-five of 250 NAFLD patients with fatty liver on ultrasound and raised enzymes (>40 IU/L) underwent liver biopsy. Patients were stratified into two groups based on their histological stage steatosis (with or without inflammation) but no fibrosis and nonalcoholic steatohepatitis (NASH) with fibrosis/cirrhosis. Serum ferritin levels were measured at the same time as getting liver biopsy. Fibroscan was carried out in each of these patients. These were compared with 50 age- and sex-matched controls with normal ultrasound, liver enzymes, and no history of alcohol. Student's t test was used as the test for significance.

RESULTS

Fifty-five NAFLD patients diagnosed on ultrasound and with raised enzymes underwent biopsy. Steatosis (with or without inflammation, but no fibrosis/ballooning) was seen in 35 patients, fibrosis/ballooning in 14 patients, and cirrhosis in 6 patients. Mean ferritin levels in groups with nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH) were 39.4 and 72.7 ng/mL, respectively (p < 0.001). The mean ferritin levels in NAFLD and controls were 51.2 and 35.2 ng/mL, respectively (p < 0.05). The area under the curve (AUC) of serum ferritin at value 48.0 ng/mL was 0.779. The coefficient of correlation between Fibroscan and serum ferritin levels was 0.9864 while that with alanine transaminase and aspartate aminotransferase was 0.69. Serum ferritin at the cutoff of 48 ng/mL differentiated significantly patients with fibrosis and higher Fibroscan levels.

CONCLUSION

Serum ferritin was low in Indian individuals, and levels even within apparently normal range indicated fibrosis and cirrhosis. A cutoff level of 48.0 IU/mL distinguished fibrosis in NAFLD. Fibroscan correlated well with serum ferritin levels.

Sulfiredoxin-1 attenuates oxidative stress via Nrf2/ARE pathway and 2-Cys Prdxs after oxygen-glucose deprivation in astrocytes

Sulfiredoxin-1 (Srxn1), an endogenous antioxidant protein, is involved in keeping the balance of the cell's oxidation/reduction and can resist oxidative stress. However, the exact antioxidant effects of Srxn1 remain fully unclear. The study aims to examine the effects of Srxn1 on oxidative stress and explore the potential mechanisms in astrocytes with 6 h/oxygen-glucose deprivation (OGD), 24 h/respiration. In the study, silencing Srxn1 was performed before exposure to 6 h/OGD, 24 h/respiration in primary astrocytes. Decreased cell viability and increased cellular damage measured by CellTiter 96H AQueous Non-Radioactive Cell Proliferation Assay (MTS) and lactate dehydrogenase (LDH) were observed in Srxn1 silencing astrocytes. In addition, Srxn1 silencing resulted in a decrease in both intracellular superoxide dismutase (SOD) and glutathione (GSH). NF-E2-related factor 2 (Nrf2), a transcription factor known to influence susceptibility to oxidative stress, upregulated Srxn1 expression during oxidative stress caused by OGD in the astrocytes. Electromobility shift assay (EMSA) demonstrated a decreased binding of Nrf2 to oligomers containing Srxn1 ter-specific antioxidant response element (ARE)-binding site in Nrf2 silencing astrocytes. We also found that a reduction of peroxiredoxin (Prdx)-SO3 was closely dependent on Srxn1. In addition, 2-Cys Prdxs protein levels were increased in the astrocytes exposed to OGD, as evaluated by immunoblot analysis. All taken together, the study suggested that silencing Srxn1 would result into increasing sensitivity to OGD-induced oxidative stress injury in astrocytes. Furthermore, Nrf2/ARE pathway was involved into Srxn1, playing its antioxidant protection against oxidative stress, all of which would provide a novel therapeutic theory for treating acute ischemic brain injury.

The effect of iron in MRI and transverse relaxation of amyloid-beta plaques in Alzheimer's disease

Dysregulation of neural iron is known to occur during the progression of Alzheimer's disease. The visualization of amyloid-beta (Aβ) plaques with MRI has largely been credited to rapid proton relaxation in the vicinity of plaques as a result of focal iron deposition. The goal of this work was to determine the relationship between local relaxation and related focal iron content associated with Aβ plaques. Alzheimer's disease (n=5) and control tissue (n=3) sample slices from the entorhinal cortex were treated overnight with the iron chelator deferoxamine or saline, and microscopic gradient-echo MRI datasets were taken. Subsequent to imaging, the same slices were stained for Aβ and iron, and then compared with regard to parametric R2 * relaxation maps and gradient-echo-weighted MR images. Aβ plaques in both chelated and unchelated tissue generated MR hypo-intensities and showed relaxation rates significantly greater than the surrounding tissue. The transverse relaxation rate associated with amyloid plaques was determined not to be solely a result of iron load, as much of the relaxation associated with Aβ plaques remained following iron chelation. The data indicate a dual relaxation mechanism associated with Aβ plaques, such that iron and plaque composition synergistically produce transverse relaxation.

Iron regulatory protein 1 sustains mitochondrial iron loading and function in frataxin deficiency

Mitochondrial iron accumulation is a hallmark of diseases associated with impaired iron-sulfur cluster (Fe-S) biogenesis, such as Friedreich ataxia linked to frataxin (FXN) deficiency. The pathophysiological relevance of the mitochondrial iron loading and the underlying mechanisms are unknown. Using a mouse model of hepatic FXN deficiency in combination with mice deficient for iron regulatory protein 1 (IRP1), a key regulator of cellular iron metabolism, we show that IRP1 activation in conditions of Fe-S deficiency increases the available cytosolic labile iron pool. Surprisingly, our data indicate that IRP1 activation sustains mitochondrial iron supply and function rather than driving detrimental iron overload. Mitochondrial iron accumulation is shown to depend on mitochondrial dysfunction and heme-dependent upregulation of the mitochondrial iron importer mitoferrin-2. Our results uncover an unexpected protective role of IRP1 in pathological conditions associated with altered Fe-S metabolism.

Cigarette smoke alters the proteomic profile of lung fibroblasts

The protein identified here may offer a new insight into deciphering damage caused by cigarette smoke.

Iron metabolism in hard ticks (Acari: Ixodidae): the antidote to their toxic diet

Ticks are notorious parasitic arthropods, known for their completely host-blood-dependent lifestyle. Hard ticks (Acari: Ixodidae) feed on their hosts for several days and can ingest blood more than a hundred times their unfed weight. Their blood-feeding habit facilitates the transmission of various pathogens. It is remarkable how hard ticks cope with the toxic nature of their blood meal, which contains several molecules that can promote oxidative stress including iron. While it is required in several physiological processes, high amounts of iron can be dangerous because iron can also participate in the formation of free radicals that may cause cellular damage and death. Here we review the current knowledge on heme and inorganic iron metabolism in hard ticks and compare it with that in vertebrates and other arthropods. We briefly discuss the studies on heme transport, storage and detoxification, and the transport and storage of inorganic iron, with emphasis on the functions of tick ferritins. This review points out other aspects of tick iron metabolism that warrant further investigation, as compared to mammals and other arthropods. Further understanding of this physiological process may help in formulating new control strategies for tick infestation and the spread of tick-borne diseases.

Serum ferritin is an important inflammatory disease marker, as it is mainly a leakage product from damaged cells

"Serum ferritin" presents a paradox, as the iron storage protein ferritin is not synthesised in serum yet is to be found there. Serum ferritin is also a well known inflammatory marker, but it is unclear whether serum ferritin reflects or causes inflammation, or whether it is involved in an inflammatory cycle. We argue here that serum ferritin arises from damaged cells, and is thus a marker of cellular damage. The protein in serum ferritin is considered benign, but it has lost (i.e. dumped) most of its normal complement of iron which when unliganded is highly toxic. The facts that serum ferritin levels can correlate with both disease and with body iron stores are thus expected on simple chemical kinetic grounds. Serum ferritin levels also correlate with other phenotypic readouts such as erythrocyte morphology. Overall, this systems approach serves to explain a number of apparent paradoxes of serum ferritin, including (i) why it correlates with biomarkers of cell damage, (ii) why it correlates with biomarkers of hydroxyl radical formation (and oxidative stress) and (iii) therefore why it correlates with the presence and/or severity of numerous diseases. This leads to suggestions for how one might exploit the corollaries of the recognition that serum ferritin levels mainly represent a consequence of cell stress and damage.

Distinct regulatory mechanisms of the human ferritin gene by hypoxia and hypoxia mimetic cobalt chloride at the transcriptional and post-transcriptional levels

Cobalt chloride has been used as a hypoxia mimetic because it stabilizes hypoxia inducible factor-1α (HIF1-α) and activates gene transcription through a hypoxia responsive element (HRE). However, differences between hypoxia and hypoxia mimetic cobalt chloride in gene regulation remain elusive. Expression of ferritin, the major iron storage protein, is regulated at the transcriptional and posttranscriptional levels through DNA and RNA regulatory elements. Here we demonstrate that hypoxia and cobalt chloride regulate ferritin heavy chain (ferritin H) expression by two distinct mechanisms. Both hypoxia and cobalt chloride increased HIF1-α but a putative HRE in the human ferritin H gene was not activated. Instead, cobalt chloride but not hypoxia activated ferritin H transcription through an antioxidant responsive element (ARE), to which Nrf2 was recruited. Intriguingly, cobalt chloride downregulated ferritin H protein expression while it upregulated other ARE-regulated antioxidant genes in K562 cells. Further characterization demonstrated that cobalt chloride increased interaction between iron regulatory proteins (IRP1 and IRP2) and iron responsive element (IRE) in the 5'UTR of ferritin H mRNA, resulting in translational block of the accumulated ferritin H mRNA. In contrast, hypoxia had marginal effect on ferritin H transcription but increased its translation through decreased IRP1-IRE interaction. These results suggest that hypoxia and hypoxia mimetic cobalt chloride employ distinct regulatory mechanisms through the interplay between DNA and mRNA elements at the transcriptional and post-transcriptional levels.

Molecular cloning and expression analysis of ferritin, heavy polypeptide 1 gene from duck (Anas platyrhynchos)

H-ferritin is a core subunit of the iron storage protein ferritin, and is related to the pathogenesis of malignant diseases. A differential expressed sequence tag of the ferritin, heavy polypeptide 1 gene (FTH1) was obtained from our previously constructed suppression subtractive cDNA library from 3-day-old ducklings challenged with duck hepatitis virus type I (DHV-1). The expression and function of FTH1 in immune defense against infection remains largely unknown in ducks. In this study, the full-length duFTH1 cDNA was obtained using reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends. It consisted of 153 basepairs (bp) 5'untranslated region (UTR), 183 bp 3'UTR, and 546 bp open reading frame that encodes a single protein of 181 amino acid residues. duFTH1 shares high similarity with FTH1 genes from other vertebrates. The amino acid sequence possesses the conserved domain of typical ferritin H subunits, including seven metal ligands in the ferroxidase center, one iron binding region signature, and a potential bio-mineralization residue (Thy(29)). Moreover, in agreement with a previously reported ferritin H subunit, we identified an iron response element in the 5'UTR. RT-PCR analyses revealed duFTH1 mRNA is widely expressed in various tissues. Real-time quantitative polymerase chain reaction analyses suggested that duFTH1 mRNA is significantly up-regulated in the liver after DHV-1 injection or polyriboinosinic polyribocytidylic acid (polyI:C) treatment, reaching a peak 4 h post-infection, and dropping progressively and returning to normal after 24 h. Our findings suggest that duFTH1 functions as an iron chelating protein subunit in duck and contributes to the innate immune responses against viral infections.

Evidence for a novel antioxidant function and isoform-specific regulation of the human p66Shc gene

p66Shc, but not p52Shc or p46Shc, is regulated by the Nrf2-ARE system, indicative of p66Shc as an antioxidant gene. p66Shc serves as an antioxidant protein in the cytoplasm, protecting cells from ROS toxicity and maintaining expression of other ARE-regulated genes. Finally, p66Shc is essential for erythroid differentiation.

The mammalian Shc family, composed of p46, p52, and p66 isoforms, serves as an adaptor protein in cell growth and stress response. p66Shc was shown to be a negative lifespan regulator by acting as a prooxidant protein in mitochondria; however, the regulatory mechanisms of p66Shc expression and function are incompletely understood. This study provides evidence for new features of p66Shc serving as an antioxidant and critical protein in cell differentiation. Unique among the Shc family, transcription of p66Shc is activated through the antioxidant response element (ARE)–nuclear factor erythroid 2–related factor 2 (Nrf2) pathway in K562 human erythroleukemia and other cell types after treatment with hemin, an iron-containing porphyrin. Phosphorylated p66Shc at Ser-36, previously reported to be prone to mitochondrial localization, is increased by hemin treatment, but p66Shc remains exclusively in the cytoplasm. p66Shc knockdown inhibits hemin-induced erythroid differentiation, in which reactive oxygen species production and apoptosis are significantly enhanced in conjunction with suppression of other ARE-dependent antioxidant genes. Conversely, p66Shc overexpression is sufficient for inducing erythroid differentiation. Collectively these results demonstrate the isoform-specific regulation of the Shc gene by the Nrf2-ARE pathway and a new antioxidant role of p66Shc in the cytoplasm. Thus p66Shc is a bifunctional protein involved in cellular oxidative stress response and differentiation.

MBD5 regulates iron metabolism via methylation-independent genomic targeting of Fth1 through KAT2A in mice

Ferritin plays important roles in iron metabolism and controls iron absorption in the intestine. The ferritin subunits ferritin heavy chain (Fth1) and ferritin light chain (Ftl1) are tightly regulated at both the transcriptional and post-transcriptional levels. However, mechanisms of maintaining stable, basal expression of Fth1 are poorly understood. Here, we show that global deletion of Mbd5 in mice induces an iron overload phenotype. Liver and serum iron levels in Mbd5(-/-) mice were 3·2-fold and 1·5-fold higher respectively, than wild-type littermates; moreover, serum ferritin was increased >5-fold in the Mbd5(-/-) mice. Mbd5 encodes a member of the methyl-CpG binding domain family; however, the precise function of this gene is poorly understood. Here, we found that intestinal Fth1 mRNA levels were decreased in Mbd5(-/-) mice. Loss of Fth1 expression in the intestine could lead to iron over-absorption. Furthermore, deleting Mbd5 specifically in the intestine resulted in a phenotype similar to that of conditional deletion of Fth1 mice. An Fth1 promoter-report luciferase assay indicated that overexpression of Mbd5 enhanced Fth1 transcription in a dose-dependent manner. Histone H4 acetylation of the Fth1 promoter was reduced in the intestine of Mbd5(-/-) mice and further analysis showed that histone acetyltransferase KAT2A was essential for MBD5-induced Fth1 transcription.

Semi-artificial and bioactive ferroxidase with nanoparticles as the active sites

L-chain apoferritin can be turned into a more stable and cellular active ferroxidase with nanoparticles as the artificial active sites.

Iron homeostasis in the liver

Iron is an essential nutrient that is tightly regulated. A principal function of the liver is the regulation of iron homeostasis. The liver senses changes in systemic iron requirements and can regulate iron concentrations in a robust and rapid manner. The last 10 years have led to the discovery of several regulatory mechanisms in the liver that control the production of iron regulatory genes, storage capacity, and iron mobilization. Dysregulation of these functions leads to an imbalance of iron, which is the primary cause of iron-related disorders. Anemia and iron overload are two of the most prevalent disorders worldwide and affect over a billion people. Several mutations in liver-derived genes have been identified, demonstrating the central role of the liver in iron homeostasis. During conditions of excess iron, the liver increases iron storage and protects other tissues, namely, the heart and pancreas from iron-induced cellular damage. However, a chronic increase in liver iron stores results in excess reactive oxygen species production and liver injury. Excess liver iron is one of the major mechanisms leading to increased steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma.

Dietary approach to decrease aging-related CNS inflammation

We demonstrate that the spontaneously hypertensive rat stroke-prone rat (SHRsp) undergoes premature aging of the CNS compared to the related normotensive Wistar Kyoto rat (WKY) as demonstrated by presence of activated microglia/macrophages, increased expression of inducible nitric oxide synthase and increased astrogliosis. We tested the hypothesis that dietary intake of phase 2 protein inducers would decrease these aging-associated degenerative changes. The source of dietary phase 2 protein inducers was dried broccoli sprouts of a cultivar containing high amounts of glucoraphanin that gives rise to phase 2 protein-inducing isothiocyanate sulforaphane. This diet significantly decreased the aging-related degenerative changes in the SHRsp CNS. We conclude that modest changes in diet may have profound effects on the aging CNS.

Concholepas concholepas Ferritin H-like subunit (CcFer): Molecular characterization and single nucleotide polymorphism associated to innate immune response

Ferritin has been identified as the principal protein of iron storage and iron detoxification, playing a pivotal role for the cellular homeostasis in living organisms. However, recent studies in marine invertebrates have suggested its association with innate immune system. In the present study, one Ferritin subunit was identified from the gastropod Concholepas concholepas (CcFer), which was fully characterized by Rapid Amplification of cDNA Ends technique. Simultaneously, a challenge test was performed to evaluate the immune response against Vibrio anguillarum. The full length of cDNA Ccfer was 1030 bp, containing 513 bp of open reading frame that encodes to 170 amino acid peptide, which was similar to the Ferritin H subunit described in vertebrates. Untranslated Regions (UTRs) were identified with a 5'UTR of 244 bp that contains iron responsive element (IRE), and a 3'UTR of 273 bp. The predicted molecular mass of deduced amino acid of CcFer was 19.66 kDa and isoelectric point of 4.92. Gene transcription analysis revealed that CcFer increases against infections with V. anguillarum, showing a peak expression at 6 h post-infection. Moreover, a single nucleotide polymorphism was detected at -64 downstream 5'UTR sequence (SNP-64). Quantitative real time analysis showed that homozygous mutant allele (TT) was significantly associated with higher expression levels of the challenged group compared to wild (CC) and heterozygous (CT) variants. Our findings suggest that CcFer is associated to innate immune response in C. concholepas and that the presence of SNPs may involve differential transcriptional expression of CcFer.

The significance of ferritin in cancer: anti-oxidation, inflammation and tumorigenesis

The iron storage protein ferritin has been continuously studied for over 70years and its function as the primary iron storage protein in cells is well established. Although the intracellular functions of ferritin are for the most part well-characterized, the significance of serum (extracellular) ferritin in human biology is poorly understood. Recently, several lines of evidence have demonstrated that ferritin is a multi-functional protein with possible roles in proliferation, angiogenesis, immunosuppression, and iron delivery. In the context of cancer, ferritin is detected at higher levels in the sera of many cancer patients, and the higher levels correlate with aggressive disease and poor clinical outcome. Furthermore, ferritin is highly expressed in tumor-associated macrophages which have been recently recognized as having critical roles in tumor progression and therapy resistance. These characteristics suggest ferritin could be an attractive target for cancer therapy because its down-regulation could disrupt the supportive tumor microenvironment, kill cancer cells, and increase sensitivity to chemotherapy. In this review, we provide an overview of the current knowledge on the function and regulation of ferritin. Moreover, we examine the literature on ferritin's contributions to tumor progression and therapy resistance, in addition to its therapeutic potential.

Genomic analysis of stress response against arsenic in Caenorhabditis elegans

Arsenic, a known human carcinogen, is widely distributed around the world and found in particularly high concentrations in certain regions including Southwestern US, Eastern Europe, India, China, Taiwan and Mexico. Chronic arsenic poisoning affects millions of people worldwide and is associated with increased risk of many diseases including arthrosclerosis, diabetes and cancer. In this study, we explored genome level global responses to high and low levels of arsenic exposure in Caenorhabditis elegans using Affymetrix expression microarrays. This experimental design allows us to do microarray analysis of dose-response relationships of global gene expression patterns. High dose (0.03%) exposure caused stronger global gene expression changes in comparison with low dose (0.003%) exposure, suggesting a positive dose-response correlation. Biological processes such as oxidative stress, and iron metabolism, which were previously reported to be involved in arsenic toxicity studies using cultured cells, experimental animals, and humans, were found to be affected in C. elegans. We performed genome-wide gene expression comparisons between our microarray data and publicly available C. elegans microarray datasets of cadmium, and sediment exposure samples of German rivers Rhine and Elbe. Bioinformatics analysis of arsenic-responsive regulatory networks were done using FastMEDUSA program. FastMEDUSA analysis identified cancer-related genes, particularly genes associated with leukemia, such as dnj-11, which encodes a protein orthologous to the mammalian ZRF1/MIDA1/MPP11/DNAJC2 family of ribosome-associated molecular chaperones. We analyzed the protective functions of several of the identified genes using RNAi. Our study indicates that C. elegans could be a substitute model to study the mechanism of metal toxicity using high-throughput expression data and bioinformatics tools such as FastMEDUSA.

Transcriptional regulation of the human ferritin gene by coordinated regulation of Nrf2 and protein arginine methyltransferases PRMT1 and PRMT4

Antioxidant genes such as ferritin are transcriptionally activated in oxidative stress via the antioxidant responsive element (ARE), to which nuclear factor-E2-related factor 2 (Nrf2) binds and activates transcription. Histone modification plays a cooperative and essential role in transcriptional regulation; however, its role in antioxidant gene transcription remains elusive. Arsenic exposure activated ferritin transcription via the ARE concomitant with increased methylation of histones H4Arg3 (H4R3) and H3Arg17 (H3R17). To test our hypothesis that histone H4R3 and H3R17 methylation regulates ferritin transcription, H4R3 and H3R17 protein arginine (R) methyltransferases 1 and 4 (PRMT1 and PRMT4) were investigated. Arsenic exposure of human HaCaT keratinocytes induced nuclear accumulation of PRMT1 and PRMT4, histone H4R3 and H3R17 methylation proximal to the ARE, but not to the non-ARE regions of ferritin genes. PRMT1 or PRMT4 knockdown did not block Nrf2 nuclear accumulation but inhibited Nrf2 binding to the AREs by ∼40% (P<0.05), thus diminishing ferritin transcription in HaCaT and human primary keratinocytes and fibroblasts, causing enhanced cellular susceptibility to arsenic toxicity as evidenced by 2-fold caspase 3 activation. Focused microarray further characterized several oxidative stress response genes are subject to PRMT1 or PRMT4 regulation. Collectively, PRMT1 and PRMT4 regulate the ARE and cellular antioxidant response to arsenic.

Genome-wide microarrray analysis reveals roles for the REF-1 family member HLH-29 in ferritin synthesis and peroxide stress response

In Caenorhabditis elegans, the six proteins that make up the REF-1 family have been identified as functional homologs of the Hairy/Enhancer of Split (HES) proteins. These transcription factors act in both Notch dependent and Notch-independent pathways to regulate embryonic events during development; however, their post-embryonic functions are not well defined. As a first step toward understanding how the REF-1 family works together to coordinate post-embryonic events, we used gene expression microarray analysis to identify transcriptional targets of HLH-29 in L4/young adult stage animals. Here we show that HLH-29 targets are genes needed for the regulation of growth and lifespan, including genes required for oxidative stress response and fatty acid metabolism, and the ferritin genes, ftn-1 and ftn-2. We show that HLH-29 regulates ftn-1 expression via promoter sequences upstream of the iron-dependent element that is recognized by the hypoxia inducible factor, HIF-1. Additionally, hlh-29 mutants are more resistant to peroxide stress than wild-type animals and ftn-1(RNAi) animals, even in the presence of excess iron. Finally we show that HLH-29 acts parallel to DAF-16 but upstream of the microphthalmia transcription factor ortholog, HLH-30, to regulate ftn-1 expression under normal growth conditions.

Multiple ferritins are vital to successful blood feeding and reproduction of the hard tick Haemaphysalis longicornis

Ticks are obligate hematophagous parasites and important vectors of diseases. The large amount of blood they consume contains great quantities of iron, an essential but also toxic element. The function of ferritin, an iron storage protein, and iron metabolism in ticks need to be further elucidated. Here, we investigated the function a newly identified secreted ferritin from the hard tick Haemaphysalis longicornis (HlFER2), together with the previously identified intracellular ferritin (HlFER1). Recombinant ferritins, expressed in Escherichia coli, were used for anti-serum preparation and were also assayed for iron-binding activity. RT-PCR and western blot analyses of different organs and developmental stages of the tick during blood feeding were performed. The localization of ferritins in different organs was demonstrated through an indirect immunofluorescent antibody test. RNA interference (RNAi) was performed to evaluate the importance of ferritin in blood feeding and reproduction of ticks. The midgut was also examined after RNAi using light and transmission electron microscopy. RT-PCR showed differences in gene expression in some organs and developmental stages. Interestingly, only HlFER2 was detected in the ovary during oviposition and in the egg despite the low mRNA transcript. RNAi induced a reduction in post-blood meal body weight, high mortality and decreased fecundity. The expression of vitellogenin genes was affected by silencing of ferritin. Abnormalities in digestive cells, including disrupted microvilli, and alteration of digestive activity were also observed. Taken altogether, our results show that the iron storage and protective functions of ferritin are crucial to successful blood feeding and reproduction of H. longicornis.

Iron increases the susceptibility of multiple myeloma cells to bortezomib

Multiple myeloma is a malignant still incurable plasma cell disorder. Pharmacological treatment based on proteasome inhibition has improved patient outcome; however, bortezomib-resistance remains a major clinical problem. Inhibition of proteasome functionality affects cellular iron homeostasis and iron is a potent inducer of reactive oxygen species and cell death, unless safely stored in ferritin. We explored the potential role of iron in bortezomib-resistance. We analyzed iron proteins, oxidative status and cell viability in 7 multiple myeloma cell lines and in plasma cells from 5 patients. Cells were treated with increasing bortezomib concentrations with or without iron supplementation. We reduced ferritin levels by both shRNA technology and by drug-induced iron starvation. Multiple myeloma cell lines are characterized by distinct ferritin levels, which directly correlate with bortezomib resistance. We observed that iron supplementation upon bortezomib promotes protein oxidation and cell death, and that iron toxicity inversely correlates with basal ferritin levels. Bortezomib prevents ferritin upregulation in response to iron, thus limiting the ability to buffer reactive oxygen species. Consequently, reduction of basal ferritin levels increases both bortezomib sensitivity and iron toxicity. In patients' cells, we confirmed that bortezomib prevents ferritin increase, that iron supplementation upon bortezomib increases cell death and that ferritin reduction overcomes bortezomib resistance. Bortezomib affects iron homeostasis, sensitizing cells to oxidative damage. Modulation of iron status is a strategy worth exploring to improve the efficacy of proteasome inhibition therapies.

Mammalian iron metabolism

ABSTRACT Iron is an essential transition metal for mammalian cellular and tissue viability. It is critical to supplying oxygen through heme, the mitochondrial respiratory chain, and enzymes such as ribonucleotide reductase. Mammalian organisms have evolved with the means of regulating the metabolism of iron, because if left unregulated, the resulting excess amounts of iron may induce chronic toxicities affecting multiple organ systems. Several homeostatic mechanisms exist to control the amount of intestinal dietary iron uptake, cellular iron uptake, distribution, and export. Within these processes, numerous molecular participants have been identified because of advancements in basic cell biology and efforts in disease-based research of iron storage abnormalities. For example, dietary iron uptake across the intestinal duodenal mucosa is mediated by an intramembrane divalent metal transporter 1 (DMT1), and cellular iron efflux involves ferroportin, the only known iron exporter. In addition to duodenal enterocytes, ferroportin is present in other cell types, and exports iron into plasma. Ferroportin was recently discovered to be regulated by the expression of the circulating hormone hepcidin, a small peptide synthesized in hepatocytes. These recent studies on the role of hepcidin in the regulation of dietary, cellular, and extracellular iron have led to a better understanding of the pathways by which iron balance in humans is influenced, especially its involvement in human genetic diseases of iron overload. Other important molecular pathways include iron binding to transferrin in the bloodstream for cellular delivery through the plasma membrane transferrin receptor (TfR1). In the cytosol, iron regulatory proteins 1 and 2 (IRP1 and IRP2) play a prominent role in sensing the presence of iron in order to posttranscriptionally regulate the expression of TfR1 and ferritin, two important participants in iron metabolism. From a toxicological standpoint, posttranscriptional regulation of these genes aids in the sequestration, control, and hence prevention of cytotoxic effects from free-floating nontransferrin-bound iron. Given the importance of dietary iron in normal physiology, its potential to induce chronic toxicity, and recent discoveries in the regulation of human iron metabolism by hepcidin, this review will address the regulatory mechanisms of normal iron metabolism in mammals with emphasis on dietary exposure. It is the goal of this review that this information may provide in a concise format our current understanding of major pathways and mechanisms involved in mammalian iron metabolism, which is a basis for control of iron toxicity. Such a discussion is intended to facilitate the identification of deficiencies so that future metabolic or toxicological studies may be appropriately focused. A better knowledge of iron metabolism from normal to pathophysiological conditions will ultimately broaden the spectrum of the usefulness of this information in biomedical and toxicological sciences for improving and protecting human health.

A precious metal: Iron, an essential nutrient for all cells

Iron is an important cofactor required for a number of essential cell functions and hence is a vital nutrient. However, iron can also be dangerous as a catalyst of free radical reactions. Accordingly, intracellular iron homeostasis and body iron balance are tightly regulated. In this review, we presented an overview of the remarkable new insights that over the last years have been gained into the multifaceted and sophisticated molecular mechanisms controlling iron acquisition, storage and release. We also reviewed the data about nutrition-related abnormalities of iron metabolism, such as iron overload and deficiency. Finally, we discussed how pathogenic microorganisms and host cells compete for iron, a battle whose outcome has a relevant role in infectious disease.

Vitamin A modulates the expression of genes involved in iron bioavailability

Iron bioavailability seems to be regulated by vitamin A (VA) but the molecular events involved in this mechanism are not well understood. It is also known that retinoids mediate most of their function via interaction with retinoid receptors, which act as ligand-activated transcription factors controlling the expression of a number of target genes. Here, we evaluated the VA effects on the modulation of the levels of mRNA encoding proteins involved in the iron bioavailability, whether in the intestinal absorption process or in the liver iron metabolism. The expression of genes involved in iron intestinal absorption (divalent metal transporter 1, duodenal cytochrome B, ferroportin 1 FPN1, and ferritin) were evaluated in vitro by treating Caco-2 cells with retinoic acid or in vivo by observing the effects of vitamin A deficiency (VAD) in BALB/C mice. Liver hepcidin and ferritin mRNA levels were upregulated by VAD; however, this condition did not promote any change on the expression of those genes that participate in the iron absorption. Moreover, data from the in vitro analysis showed that VA induced FPN1 gene expression by a hepcidin-independent manner. Therefore, the in vivo results support the idea that VAD may not affect iron absorption but would rather affect iron mobilization mechanisms. On the other hand, our results using Caco-2 cells raises the possibility that VA addition to intestinal epithelium may improve iron absorption through the induction of FPN1 gene expression.

Cloning analysis of ferritin and the cisplatin-subunit for cancer cell apoptosis in Aplysia juliana hepatopancreas

Ferritin, an iron storage protein, plays a key role in iron metabolism in vivo. Here, we have cloned an inducible ferritin cDNA with 519 bp within the open reading frame fragment from the hepatopancreas of Aplysia juliana (AJ). The subunit sequence of the ferritin was predicted to be a polypeptide of 172 amino acids with a molecular mass of 19.8291kDa and an isoelectric point of 5.01. The cDNA sequence of hepatopancreas ferritin in AJ was constructed into a pET-32a system for expressing its relative protein efficiently in E. coli strain BL21, under isopropyl-β-d-thiogalactoside induction. The recombinant ferritin, which was further purified on a Ni-NTA resin column and digested with enterokinase, was detected as a single subunit of approximately 20 kDa mass using both SDS-PAGE and mass spectrometry. The secondary structure and phosphorylation sites of the deduced amino acids were predicted using both ExPASy proteomic tools and the NetPhos 2.0 server, and the subunit space structure of the recombinant AJ ferritin (rAjFer) was built using a molecular operating environment software system. The result of in-gel digestion and identification using MALDI-TOF MS/MS showed that the recombinant protein was AjFer. ICP-MS results indicated that the rAjFer subunit could directly bind to cisplatin[cis-Diaminedichloroplatinum(CDDP)], giving approximately 17.6 CDDP/ferritin subunits and forming a novel CDDP-subunit. This suggests that a nanometer CDDP core-ferritin was constructed, which could be developed as a new anti-cancer drug. The flow cytometry results indicated that CDDP-rAjFer could induce Hela cell apoptosis. Results of the real-time PCR and Western blotting showed that the expression of AjFer mRNA was up-regulated in AJ under Cd(2+) stress. The recombinant AjFer protein should prove to be useful for further study of the structure and function of ferritin in Aplysia.

Expression of the H- and L-subunits of ferritin in bone marrow macrophages of patients with osteoarthritis

Osteoarthritis is a disease characterized by an increase in the production of reactive oxygen species (ROS) in afflicted joints. Excess iron, due to its role in the production of ROS and crystal deposition in the joints, is implicated in the disease progression of osteoarthritis. Ferritin is a major regulator of the bioavailability of iron, and its functions are determined largely by the combination of H- and L-subunits present in its outer protein shell. The purpose of the study was to investigate the expression of the H- and L-subunits of ferritin in bone marrow macrophages of osteoarthritis patients. The cytokine profiles were assessed as cytokines play an important role in the expression of the ferritin subunits. The H-subunit of ferritin in the bone marrow macrophages was significantly higher (P value = 0.035) in the osteoarthritis patients compared with the controls (107.84; 69.25-167.94 counts/μm(2); n = 7 versus 71.07; 58.56-86.26 counts/μm(2); n = 19). A marginally significant increase (P value = 0.059) was shown for the expression of the L-subunit in the osteoarthritis patients compared with the controls (133.03; 104.04-170.10 counts/μm(2); n = 7 versus 104.23; 91.53-118.70 counts/μm(2); n = 19). The osteoarthritis and control groups had comparable C-reactive protein, as well as proinflammatory and anti-inflammatory cytokine concentrations. The major exception was for transforming growth factor-β (TGF-β), which was higher (P value = 0.014) in the plasma of the osteoarthritis patients (16.69; 13.09-21.28 ng/mL; n = 7 versus 8.60; 6.34-11.67 ng/mL; n = 19). Up-regulation of the ferritin subunits decreases the levels of bioavailable iron and provides protection against the unwarranted production of ROS and crystal deposition. A role for TGF-β in the up-regulation of the expression of the H-subunit, and possibly the L-subunit, of ferritin is postulated in osteoarthritis.

Genetic ablation of Nrf2/antioxidant response pathway in Alexander disease mice reduces hippocampal gliosis but does not impact survival

In Alexander disease (AxD) the presence of mutant glial fibrillary acidic protein (GFAP), the major intermediate filament of astrocytes, triggers protein aggregation, with marked induction of a stress response mediated by the transcription factor, Nrf2. To clarify the role of Nrf2 in AxD, we have crossed Gfap mutant and transgenic mouse models into an Nrf2 null background. Deletion of Nrf2 eliminates the phase II stress response normally present in mouse models of AxD, but causes no change in body weight or lifespan, even in a severe lethal model. AxD astrocytes without Nrf2 retain features of reactivity, such as expression of the endothelin-B receptor, but have lower Gfap levels, a decrease in p62 protein and reduced iron accumulation, particularly in hippocampus. Microglial activation, indicated by Iba1 expression, is also diminished. Although the Nrf2 response is generally considered beneficial, these results show that in the context of AxD, loss of the antioxidant pathway has no obvious negative effects, while actually decreasing Gfap accumulation and pathology. Given the attention Nrf2 is receiving as a potential therapeutic target in AxD and other neurodegenerative diseases, it will be interesting to see whether induction of Nrf2, beyond the endogenous response, is beneficial or not in these same models.

Reactive oxygen species (ROS) homeostasis and redox regulation in cellular signaling

Reactive oxygen species (ROS) are generated during mitochondrial oxidative metabolism as well as in cellular response to xenobiotics, cytokines, and bacterial invasion. Oxidative stress refers to the imbalance due to excess ROS or oxidants over the capability of the cell to mount an effective antioxidant response. Oxidative stress results in macromolecular damage and is implicated in various disease states such as atherosclerosis, diabetes, cancer, neurodegeneration, and aging. Paradoxically, accumulating evidence indicates that ROS also serve as critical signaling molecules in cell proliferation and survival. While there is a large body of research demonstrating the general effect of oxidative stress on signaling pathways, less is known about the initial and direct regulation of signaling molecules by ROS, or what we term the "oxidative interface." Cellular ROS sensing and metabolism are tightly regulated by a variety of proteins involved in the redox (reduction/oxidation) mechanism. This review focuses on the molecular mechanisms through which ROS directly interact with critical signaling molecules to initiate signaling in a broad variety of cellular processes, such as proliferation and survival (MAP kinases, PI3 kinase, PTEN, and protein tyrosine phosphatases), ROS homeostasis and antioxidant gene regulation (thioredoxin, peroxiredoxin, Ref-1, and Nrf-2), mitochondrial oxidative stress, apoptosis, and aging (p66Shc), iron homeostasis through iron-sulfur cluster proteins (IRE-IRP), and ATM-regulated DNA damage response.

Alternative ferritin mRNA translation via internal initiation

Ferritin stores and detoxifies an excess of intracellular iron, and thereby plays an important role in the metabolism of this metal. As unshielded iron promotes oxidative stress, ferritin is crucial in maintaining cellular redox balance and may also modulate cell growth, survival, and apoptosis. The expression of ferritin is controlled by transcriptional and post-transcriptional mechanisms. In light of the well-established transcriptional induction of ferritin by inflammatory signals, we examined how ferritin mRNA translation responds to stress conditions. We first used HT1080 fibrosarcoma cells engineered for coumermycin-inducible expression of PKR, a stress kinase that inhibits protein synthesis in virus-infected cells by phosphorylating eIF2α. In this setting, iron triggered partial ferritin mRNA translation despite a PKR-induced global shutdown in protein synthesis. Moreover, iron-mediated ferritin synthesis was evident in cells infected with an attenuated strain of poliovirus; when eIF4GI was cleaved, eIF2α was phosphorylated, and host protein synthesis was inhibited. Under global inhibition of protein synthesis or specific inhibition of ferritin mRNA translation in cells overexpressing PKR or IRP1, respectively, we demonstrate association of ferritin mRNA with heavy polysomes. Further experiments revealed that the 5' untranslated region (5' UTR) of ferritin mRNA contains a bona fide internal ribosomal entry site (IRES). Our data are consistent with the existence of an alternative, noncanonical mechanism for ferritin mRNA translation, which may primarily operate under stress conditions to protect cells from oxidative stress.

Iron homeostasis in astrocytes and microglia is differentially regulated by TNF-α and TGF-β1

Abnormal iron homeostasis is increasingly thought to contribute to the pathogenesis of several neurodegenerative disorders. We have previously reported impaired iron homeostasis in a mouse model of spinal cord injury and in a mouse model of amyotrophic lateral sclerosis. Both these disorders are associated with CNS inflammation. However, what effect inflammation, and in particular, inflammatory cytokines have on iron homeostasis in CNS glia remains largely unknown. Here we report that the proinflammatory cytokine TNF-α, and the anti-inflammatory cytokine TGF-β1 affect iron homeostasis in astrocytes and microglia in distinct ways. Treatment of astrocytes in vitro with TNF-α induced the expression of the iron importer "divalent iron transporter 1" (DMT1) and suppressed the expression of the iron exporter ferroportin (FPN). However, TGF-β1 had no effect on DMT1 expression but increased the expression of FPN in astrocytes. In microglia, on the other hand, both cytokines caused induction of DMT1 and suppression of FPN expression. Iron influx and efflux assays in vitro confirmed that iron homeostasis in astrocytes and microglia is differentially regulated by these cytokines. In particular, TNF-α caused an increase in iron uptake and retention by both astrocytes and microglia, while TGF-β1 promoted iron efflux from astrocytes but caused iron retention in microglia. These data suggest that these two cytokines, which are expressed in CNS inflammation in injury and disease, can have profound and divergent effects on iron homeostasis in astrocytes and microglia.

Reactive oxygen species (ROS) homeostasis and redox regulation in cellular signaling

Reactive oxygen species (ROS) are generated during mitochondrial oxidative metabolism as well as in cellular response to xenobiotics, cytokines, and bacterial invasion. Oxidative stress refers to the imbalance due to excess ROS or oxidants over the capability of the cell to mount an effective antioxidant response. Oxidative stress results in macromolecular damage and is implicated in various disease states such as atherosclerosis, diabetes, cancer, neurodegeneration, and aging. Paradoxically, accumulating evidence indicates that ROS also serve as critical signaling molecules in cell proliferation and survival. While there is a large body of research demonstrating the general effect of oxidative stress on signaling pathways, less is known about the initial and direct regulation of signaling molecules by ROS, or what we term the "oxidative interface." Cellular ROS sensing and metabolism are tightly regulated by a variety of proteins involved in the redox (reduction/oxidation) mechanism. This review focuses on the molecular mechanisms through which ROS directly interact with critical signaling molecules to initiate signaling in a broad variety of cellular processes, such as proliferation and survival (MAP kinases, PI3 kinase, PTEN, and protein tyrosine phosphatases), ROS homeostasis and antioxidant gene regulation (thioredoxin, peroxiredoxin, Ref-1, and Nrf-2), mitochondrial oxidative stress, apoptosis, and aging (p66Shc), iron homeostasis through iron-sulfur cluster proteins (IRE-IRP), and ATM-regulated DNA damage response.

Serum ferritin is an independent predictor of histologic severity and advanced fibrosis in patients with nonalcoholic fatty liver disease

Serum ferritin (SF) levels are commonly elevated in patients with nonalcoholic fatty liver disease (NAFLD) because of systemic inflammation, increased iron stores, or both. The aim of this study was to examine the relationship between elevated SF and NAFLD severity. Demographic, clinical, histologic, laboratory, and anthropometric data were analyzed in 628 adult patients with NAFLD (age, ≥ 18 years) with biopsy-proven NAFLD and an SF measurement within 6 months of their liver biopsy. A threshold SF >1.5 × upper limit of normal (ULN) (i.e., >300 ng/mL in women and >450 ng/mL in men) was significantly associated with male sex, elevated serum alanine aminotransferase, aspartate aminotransferase, iron, transferrin-iron saturation, iron stain grade, and decreased platelets (P < 0.01). Histologic features of NAFLD were more severe among patients with SF >1.5 × ULN, including steatosis, fibrosis, hepatocellular ballooning, and diagnosis of NASH (P < 0.026). On multiple regression analysis, SF >1.5 × ULN was independently associated with advanced hepatic fibrosis (odds ratio [OR], 1.66; 95% confidence interval [CI], 1.05-2.62; P = 0.028) and increased NAFLD Activity Score (NAS) (OR, 1.99; 95% CI, 1.06-3.75; P = 0.033).

CONCLUSIONS

A SF >1.5 × ULN is associated with hepatic iron deposition, a diagnosis of NASH, and worsened histologic activity and is an independent predictor of advanced hepatic fibrosis among patients with NAFLD. Furthermore, elevated SF is independently associated with higher NAS, even among patients without hepatic iron deposition. We conclude that SF is useful to identify NAFLD patients at risk for NASH and advanced fibrosis.

Effects of oxidative stress caused by tert-butylhydroquinone on cytotoxicity in MDCK cells

Antioxidant and oxidative stress effects of prooxidants are generally dose-dependent, and these effects depend on the prooxidant species and cell type. However, the cellular response to oxidant challenge is a complicated interplay of events involving cellular expression of phase II detoxification enzymes and cellular metal metabolism. This study demonstrates the effect of tert-butylhydroquinone (t-BHQ)-induced oxidative stress on MDCK cells. Cell toxicity tests were carried out using the crystal violet (CV) assay with the following prooxidants: t-BHQ, diethyl maleate (DEM), hydrogen peroxide (H(2)O(2)), diquat (DQ) and β-naphthoflavone (β-NF). Except for β-NF, these prooxidants showed dose-dependent cytotoxicity besides the most potent t-BHQ cytotoxicity. Only t-BHQ and DEM caused significant time-dependent expression of ferritin protein as an antioxidant, which segregates Fe(2+), causing the Fenton reaction. t-BHQ and DEM increased formation of lipid peroxidation, but DQ showed a tendency to decrease lipid peroxidation levels. In XTT assay, even when substantial cell death was observed in the CV assay, t-BHQ appeared to increase cell viability by enhancing XTT reduction, likely through the production of NADPH. Although curcumin, which induces cytoprotective phase II enzymes and chelates metal irons, decreased cell viability, it inhibited t-BHQ cytotoxicity. These results indicate that t-BHQ exhibits strong cytotoxicity against MDCK cells, an effect mitigated by curcumin, and that t-BHQ-induced oxidative stress activates the pentose phosphate pathway.

Basic principles and emerging concepts in the redox control of transcription factors

Convincing concepts of redox control of gene transcription have been worked out for prokaryotes and lower eukaryotes, whereas the knowledge on complex mammalian systems still resembles a patchwork of poorly connected findings. The article, therefore, reviews principles of redox regulation with special emphasis on chemical feasibility, kinetic requirements, specificity, and physiological context, taking well investigated mammalian transcription factor systems, nuclear transcription factor of bone marrow-derived lymphocytes (NF-κB), and kelch-like ECH-associated protein-1 (Keap1)/Nrf2, as paradigms. Major conclusions are that (i) direct signaling by free radicals is restricted to O(2)•- and •NO and can be excluded for fast reacting radicals such as •OH, •OR, or Cl•; (ii) oxidant signals are H(2)O(2), enzymatically generated lipid hydroperoxides, and peroxynitrite; (iii) free radical damage is sensed via generation of Michael acceptors; (iv) protein thiol oxidation/alkylation is the prominent mechanism to modulate function; (v) redox sensors must be thiol peroxidases by themselves or proteins with similarly reactive cysteine or selenocysteine (Sec) residues to kinetically compete with glutathione peroxidase (GPx)- and peroxiredoxin (Prx)-type peroxidases or glutathione-S-transferases, respectively, a postulate that still has to be verified for putative mammalian sensors. S-transferases and Prxs are considered for system complementation. The impact of NF-κB and Nrf2 on hormesis, management of inflammatory diseases, and cancer prevention is critically discussed.

Single subunit type of ferritin from visceral mass of Saccostrea cucullata: cloning, expression and cisplatin-subunit analysis

Ferritin, the iron storage protein, plays a key role in iron metabolism. Here, we have cloned an inducible ferritin cDNA with 516 bp within the open reading frame fragment from the visceral mass of Saccostrea cucullata. The subunit sequence of the ferritin was predicted to be a polypeptide of 171 amino acids with a molecular weight (MW) of 19.9182 kDa and an isoelectric point of 5.24. The cDNA sequence of S. cucullata ferritin was constructed into a pET-32a expression system for expressing its relative protein efficiently in the Escherichia coli BL21 strain under isopropyl-β-D-thiogalactoside (IPTG) induction. The recombinant ferritin, which was further purified on a Ni-NTA resin column and digested with enterokinase, was detected as a single subunit of approximately MW 20 kDa using both SDS-PAGE and mass spectrometry. S. cucullata ferritin (ScFer) showed 98% identity with Crassostrea gigas ferritin at the amino acid level. The secondary structure and phosphorylation sites of deduced amino acids were predicted with ExPASy proteomics tools and the NetPhos 2.0 server, respectively, and the subunit space structure of recombinant S. cucullata ferritin (rScFer) was built using the molecular operating environmental software system. The results of both in-gel digestion and identification using MALDI-TOF MS/MS showed that the recombinant protein was ScFer. ICP-MS indicated that rScFer subunit can directly bind to cisplatin[cis-Diaminedichloroplatinum(CDDP)], giving approximately 22.9 CDDP/ferritin subunit for forming a novel complex of CDDP-subunit, which suggests that it constructs a nanometer CDDP core-ferritin for developing a new drug of anti-cancer. The results of both the real-time PCR and Western blotting showed that the expression of ScFer mRNA was up-regulated in the oyster under the stress of Cd(2+). In addition, the expression increment of ScFer mRNA under bacterial challenge indicated that ferritin participated in the immune response of S. cucullata. The recombinant ScFer should prove to be useful for further study of the structure and function of ferritin in S. cucullata.

Structural and functional analyses of chicken liver ferritin

Characterization of ferritins from different species has provided insight into iron regulation mechanisms and evolutionary relationships. Here, we examined chicken liver ferritin, which comprises only H subunit and has 14.8 µg of Fe/100 µg of protein. The chicken H subunit apo homopolymer showed the same iron uptake rate as bovine H subunit homopolymer expressed with a baculovirus expression system (0.31 and 0.28 mmol of Fe/min per micromole of protein for chicken and bovine H subunit, respectively). Chicken H subunit apo homopolymer showed a significantly higher biotinylated hemin-binding activity than liver holoferritin. Although bovine spleen apoferritin, which has an L (liver or light):H (heart or heavy) subunit ratio of 1:1, also shows a significantly higher biotinylated hemin-binding activity than its holoferritin, these biotinylated hemin-binding activities were markedly lower than those of both chicken holo- and apoferritins. Binding of chicken holo- and apoferritin with biotinylated hemin was strongly inhibited by hemin but not iron-free hemin, protoporphyrin IX, or Zn-protoporphyrin. These findings demonstrate that chicken ferritin comprises only an H subunit, possesses ferroxidase activity as in mammalian ferritin H subunits, and binds heme more strongly than mammalian ferritins.

Antioxidants in foods: state of the science important to the food industry

Antioxidant foods and ingredients are an important component of the food industry. In the past, antioxidants were used primarily to control oxidation and retard spoilage, but today many are used because of putative health benefits. However, the traditional message that oxidative stress, which involves the production of reactive oxygen species (ROS), is the basis for chronic diseases and aging is being reexamined. Accumulating evidence suggests that ROS exert essential metabolic functions and that removal of too many ROS can upset cell signaling pathways and actually increase the risk of chronic disease. It is imperative that the food industry be aware of progress in this field to present the science relative to foods in a forthright and clear manner. This may mean reexamining the health implications of adding large amounts of antioxidants to foods.

Effect of diquat-induced oxidative stress on iron metabolism in male Fischer-344 rats

Diquat toxicity causes iron-mediated oxidative stress; however, it remains unclear how diquat affects iron metabolism. Here, we examined the effect of diquat-induced oxidative stress on iron metabolism in male Fischer-344 rats, with particular focus on gene expression. Hepatic nonheme iron content was unchanged until 20 h after diquat treatment. Hepatic free iron levels increased markedly in the early stages following treatment and remained elevated for at least 6 h, resulting in severe hepatotoxicity, until returning to control levels at 20 h. The level of hepatic ferritin, especially the H-subunit, increased 20 h after diquat treatment due to elevated hepatic ferritin-H mRNA expression. These results indicate that early elevated levels of free iron in the liver of diquat-treated rats cause hepatotoxicity, and that this free iron is subsequently sequestered by ferritin synthesized under conditions of oxidative stress, thus limiting the pro-oxidant challenge of iron. The plasma iron concentration decreased at 6 and 20 h after diquat treatment, whereas the level of plasma interleukin-6 increased markedly at 3 h and remained high until 20 h. In the liver of diquat-treated rats, expression of hepcidin mRNA was markedly upregulated at 3 and 6 h, whereas ferroportin mRNA expression was downregulated slightly at 20 h. Transferrin receptor 1 mRNA expression was significantly upregulated at 3, 6, and 20 h. These results indicate that inhibition of iron release from iron-storage tissues, through stimulation of the interleukin-6-hepcidin-ferroportin axis, and enhanced iron uptake into hepatocytes, mediated by transferrin receptor 1, cause hypoferremia.

Cell sensitivity to oxidative stress is influenced by ferritin autophagy

To test the consequences of lysosomal degradation of differently iron-loaded ferritin molecules and to mimic ferritin autophagy under iron-overload and normal conditions, J774 cells were allowed to endocytose heavily iron loaded ferritin, probably with some adventitious iron (Fe-Ft), or iron-free apo-ferritin (apo-Ft). When cells subsequently were exposed to a bolus dose of hydrogen peroxide, apo-Ft prevented lysosomal membrane permeabilization (LMP), whereas Fe-Ft enhanced LMP. A 4-h pulse of Fe-Ft initially increased oxidative stress-mediated LMP that was reversed after another 3h under standard culture conditions, suggesting that lysosomal iron is rapidly exported from lysosomes, with resulting upregulation of apo-ferritin that supposedly is autophagocytosed, thereby preventing LMP by binding intralysosomal redox-active iron. The obtained data suggest that upregulation of the stress protein ferritin is a rapid adaptive mechanism that counteracts LMP and ensuing apoptosis during oxidative stress. In addition, prolonged iron starvation was found to induce apoptotic cell death that, interestingly, was preceded by LMP, suggesting that LMP is a more general phenomenon in apoptosis than so far recognized. The findings provide new insights into aging and neurodegenerative diseases that are associated with enhanced amounts of cellular iron and show that lysosomal iron loading sensitizes to oxidative stress.

Regulation of neuronal ferritin heavy chain, a new player in opiate-induced chemokine dysfunction

The heavy chain subunit of ferritin (FHC), a ubiquitous protein best known for its iron-sequestering activity as part of the ferritin complex, has recently been described as a novel inhibitor of signaling through the chemokine receptor CXCR4. Levels of FHC as well as its effects on CXCR4 activation increase in cortical neurons exposed to mu-opioid receptor agonists such as morphine, an effect likely specific to neurons. Major actions of CXCR4 signaling in the mature brain include a promotion of neurogenesis, activation of pro-survival signals, and modulation of excitotoxic pathways; thus, FHC up-regulation may contribute to the neuronal dysfunction often associated with opiate drug abuse. This review summarizes our knowledge of neuronal CXCR4 function, its regulation by opiates and the role of FHC in this process, and known mechanisms controlling FHC production. We speculate on the mechanism involved in FHC regulation by opiates and offer FHC as a new target in opioid-induced neuropathology.

Depressed levels of interferon-gamma and HLA-DR+CD3+ T cells in infants with transient hyperferritinemia

Familial hemophagocytic lymphohistiocytosis (FHL), which typically has its onset during infancy, is uniformly fatal if not treated. It therefore requires prompt therapeutic intervention. Although hyperferritinemia has been emphasized as a useful marker for FHL, some nonfatal cases in infants with spontaneous remission also manifest with hyperferritinemia. However, distinguishing them is difficult because initial clinical features of these infants are similar. The authors encountered 14 infants with hyperferritinemia (serum ferritin >674 ng/mL), which normalized within 3 weeks following a benign clinical course. The authors compared the levels of HLA-DR+CD3+ T-cell subsets and interferon-gamma (IFN-γ) in the peripheral blood between these infants and FHL cases: one of the authors' own patients and others from the literature. Serum IFN-γ was not detected in infants with hyperferritinemia. Moreover, levels of HLA-DR+CD3+ T cells were extremely depressed. In contrast, serum IFN-γ was elevated and HLA-DR+CD3+ T cells were not depressed in FHL. Measurement of activated T cells and serum IFN-γ might help differentiate FHL in febrile infants with transient hyperferritinemia.