Systems genetic analysis of peripheral iron parameters in the mouse

Lipopolysaccharide-binding protein (LBP) can reverse the amyloid state of fibrin seen or induced in Parkinson's disease

The thrombin-induced polymerisation of fibrinogen to form fibrin is well established as a late stage of blood clotting. It is known that Parkinson's Disease (PD) is accompanied by dysregulation in blood clotting, but it is less widely known as a coagulopathy. In recent work, we showed that the presence of tiny amounts of bacterial lipopolysaccharide (LPS) in healthy individuals could cause clots to adopt an amyloid form, and this could be observed via scanning electron microscopy (SEM) or via the fluorescence of thioflavin-T. This could be prevented by the prior addition of lipopolysaccharide-binding protein (LBP). We had also observed by SEM this unusual clotting in the blood of patients with Parkinson's Disease. We hypothesised, and here show, that this too can be prevented by LBP in the context of PD. This adds further evidence implicating inflammatory microbial cell wall products as an accompaniment to the disease, and may be part of its aetiology. This may lead to novel treatment strategies in PD designed to target microbes and their products.

Hamp1 mRNA and plasma hepcidin levels are influenced by sex and strain but do not predict tissue iron levels in inbred mice

Iron homeostasis is tightly regulated, and the peptide hormone hepcidin is considered to be a principal regulator of iron metabolism. Previous studies in a limited number of mouse strains found equivocal sex- and strain-dependent differences in mRNA and serum levels of hepcidin and reported conflicting data on the relationship between hepcidin (Hamp1) mRNA levels and iron status. Our aim was to clarify the relationships between strain, sex, and hepcidin expression by examining multiple tissues and the effects of different dietary conditions in multiple inbred strains. Two studies were done: first, Hamp1 mRNA, liver iron, and plasma diferric transferrin levels were measured in 14 inbred strains on a control diet; and second, Hamp1 mRNA and plasma hepcidin levels in both sexes and iron levels in the heart, kidneys, liver, pancreas, and spleen in males were measured in nine inbred/recombinant inbred strains raised on an iron-sufficient or high-iron diet. Both sex and strain have a significant effect on both hepcidin mRNA (primarily a sex effect) and plasma hepcidin levels (primarily a strain effect). However, liver iron and diferric transferrin levels are not predictors of Hamp1 mRNA levels in mice fed iron-sufficient or high-iron diets, nor are the Hamp1 mRNA and plasma hepcidin levels good predictors of tissue iron levels, at least in males. We also measured plasma erythroferrone, performed RNA-sequencing analysis of liver samples from six inbred strains fed the iron-sufficient, low-iron, or high-iron diets, and explored differences in gene expression between the strains with the highest and lowest hepcidin levels.NEW & NOTEWORTHY Both sex and strain have a significant effect on both hepcidin mRNA (primarily a sex effect) and plasma hepcidin levels (primarily a strain effect). Liver iron and diferric transferrin levels are not predictors of Hamp1 mRNA levels in mice, nor are the Hamp1 mRNA and plasma hepcidin levels good predictors of tissue iron levels, at least in males.

Diurnal variations in brain iron concentrations in BXD RI mice

Under normal and dietary iron deficiency conditions, the BXD recombinant inbred (RI) strains of mice show large variations in regional brain iron concentration, particularly in the ventral midbrain (VMB). In a study utilizing just one of the BXD strains, diurnal changes in subregional brain iron concentration were found, which were dependent on the brain region and sex of the mice. The focus of this study was to determine if diurnal changes in VMB can be found across other BXD RI strains and whether a diurnal effect would be common to all strains or variable across strains similar to the large strain variability in iron concentrations determined during the first part of the light phase. Eight RI (BXD type) strains of mice of both sexes were selected for this study. Mice were sacrificed at postnatal day 120: half in the light phase (LP) and half in the dark phase (DP) of the light-dark cycle. Iron concentrations were determined in VMB, which was the primary region of interest, and five other brain regions. Exploratory analysis was also done on liver and spleen iron concentrations to assess for diurnal changes. Three strains showed clear diurnal variation in iron in the VMB and the others strains showed diurnal variations in other regions. These changes were not equally apparent in both sexes. Exploratory analysis also found strain×sex-dependent diurnal differences in spleen and liver iron. In conclusion, significant brain-regional-specific diurnal changes in total iron concentrations were found in a selection of BXD RI mice. Sex and strain are functional determinates of which regions will be affected and in what direction the affect will be. The study provides an animal model for future work into determining the biological and genetic basis of circadian influences on VMB iron homeostasis.

Unbiased RNAi screen for hepcidin regulators links hepcidin suppression to proliferative Ras/RAF and nutrient-dependent mTOR signaling

The hepatic hormone hepcidin is a key regulator of systemic iron metabolism. Its expression is largely regulated by 2 signaling pathways: the "iron-regulated" bone morphogenetic protein (BMP) and the inflammatory JAK-STAT pathways. To obtain broader insights into cellular processes that modulate hepcidin transcription and to provide a resource to identify novel genetic modifiers of systemic iron homeostasis, we designed an RNA interference (RNAi) screen that monitors hepcidin promoter activity after the knockdown of 19 599 genes in hepatocarcinoma cells. Interestingly, many of the putative hepcidin activators play roles in signal transduction, inflammation, or transcription, and affect hepcidin transcription through BMP-responsive elements. Furthermore, our work sheds light on new components of the transcriptional machinery that maintain steady-state levels of hepcidin expression and its responses to the BMP- and interleukin-6-triggered signals. Notably, we discover hepcidin suppression mediated via components of Ras/RAF MAPK and mTOR signaling, linking hepcidin transcriptional control to the pathways that respond to mitogen stimulation and nutrient status. Thus using a combination of RNAi screening, reverse phase protein arrays, and small molecules testing, we identify links between the control of systemic iron homeostasis and critical liver processes such as regeneration, response to injury, carcinogenesis, and nutrient metabolism.

Fine-mapping and genetic analysis of the loci affecting hepatic iron overload in mice

The liver, as the major organ for iron storage and production of hepcidin, plays pivotal roles in maintaining mammalian iron homeostasis. A previous study showed that Quantitative Trait Loci (QTLs) on chromosome 7 (Chr7) and 16 (Chr16) may control hepatic non-heme iron overload in an F2 intercross derived from C57BL/6J (B6) and SWR/J (SWR) mice. In this study, we aimed to validate the existence of these loci and identify the genes responsible for the phenotypic variations by generating congenic mice carrying SWR chromosome segments expanding these QTLs (D7Mit68-D7Mit71 and D16Mit125-D16Mit185, respectively). We excluded involvement of Chr7 based on the lack of iron accumulation in congenic mice. In contrast, liver iron accumulation was observed in Chr16 congenic mice. Through use of a series of subcongenic murine lines the interval on Chr16 was further fine-mapped to a 0.8 Mb segment spanning 11 genes. We found that the mRNA expression pattern in the liver remained unchanged for all 11 genes tested. Most importantly, we detected 4 missense mutations in 3 candidate genes including Sidt1 (P172R), Spice1(R708S), Boc (Q1051R) and Boc (S450-insertion in B6 allele) in the liver of SWR homozygous congenic mice. To further delineate potential modifier gene(s), we reconstituted seven candidate genes, Sidt1, Boc, Zdhhc23, Gramd1c, Atp6v1a, Naa50 and Gtpbp8, in mouse liver through hydrodynamic transfection. However, we were unable to detect significant changes in liver iron levels upon reconstitution of these candidate genes. Taken together, our work provides strong genetic evidence of the existence of iron modifiers on Chr16. Moreover, we were able to delineate the phenotypically responsible region to a 0.8 Mb region containing 11 coding genes, 3 of which harbor missense mutations, using a series of congenic mice.

Effects of IV iron isomaltoside-1000 treatment on regional brain iron status in an iron-deficient animal

BACKGROUND

Iron deficiency has been documented to affect human cognitive function and conditions with brain iron compromise such as the restless legs syndrome (RLS). Intravenous (IV) iron treatment is used to reduce iron deficiency but its effects on brain iron are not known. It is not known if IV iron is effective in correcting regional brain iron deficiencies nor if it poses a risk of producing iron overload in some brain regions. Preclinical study of IV iron in the iron-deficient (ID) murine model is needed to evaluate and develop IV iron treatments for brain iron deficiency.

METHODS

Response to tail vein injections of iron (iron isomaltoside-1000, dose equivalent to 1000 mg for 75 kg adult) or vehicle were evaluated for ID mice by microdialysis assessing non-transferrin bound (NTB) iron in the ventral midbrain (VMB) and autopsy at 3 and 10 days post-injection assessing iron content in critical brain regions.

RESULTS

The ID mice showed marked circadian variation in NTB extracellular iron. After iron injection, NTB iron was rapidly increased in the VMB and then decreased over 12h to the levels observed for vehicle. Regional brain iron content at 3 and 10 days post-injection in the iron- compared to vehicle-treated group showed significantly more iron for the VMB and nucleus accumbens but not for the other regions (i.e. prefrontal cortex, caudate-putamen, cerebellum, and pons), which also did not show decreased iron content with the ID diet.

CONCLUSION

Iron isomaltoside-1000 given IV corrects the regional brain iron deficiency in these ID mice without producing iron overload in any of the brain regions studied. This is the first demonstration of effects of IV iron in the brain and it provides a useful preclinical model for this assessment, particularly relevant for developing iron treatments for conditions with problematic iron deficiency, e.g. RLS.

Systems genetic analysis of the effects of iron deficiency in mouse brain

Iron regulation in the brain is both necessary and highly complex. Too little or too much iron can compromise neurological function, yet we still do not know all of the regulatory processes. In our research, we seek to identify genes and gene networks underlying individual differences in brain iron regulation. To this end, we fed mice from 20+ inbred strains a diet low in iron from weaning to 4 months of age. At sacrifice, we measured iron content in the ventral midbrain (VMB). The VMB contains the substantia nigra, a region particularly vulnerable to iron imbalance. The results showed high, inter-strain variability in dietary iron reduction, from almost no loss to more than 40 % vs. control. When we performed quantitative trait loci (QTL) analysis, we observed a significant area on chromosome 2. Within this QTL, we selected glial high-affinity glutamate transporter 1 (Glt1) as the leading candidate. Expression of this gene is both correlated with VMB iron and is also cis-modulated by local sequence variants that segregate in the BXD family. VMB expression differences of Glt1 in six strains covary with differential susceptibility to VMB iron loss.

Systems genetic analysis of multivariate response to iron deficiency in mice

The aim of this study was to identify genes that influence iron regulation under varying dietary iron availability. Male and female mice from 20+ BXD recombinant inbred strains were fed iron-poor or iron-adequate diets from weaning until 4 mo of age. At death, the spleen, liver, and blood were harvested for the measurement of hemoglobin, hematocrit, total iron binding capacity, transferrin saturation, and liver, spleen and plasma iron concentration. For each measure and diet, we found large, strain-related variability. A principal-components analysis (PCA) was performed on the strain means for the seven parameters under each dietary condition for each sex, followed by quantitative trait loci (QTL) analysis on the factors. Compared with the iron-adequate diet, iron deficiency altered the factor structure of the principal components. QTL analysis, combined with PosMed (a candidate gene searching system) published gene expression data and literature citations, identified seven candidate genes, Ptprd, Mdm1, Picalm, lip1, Tcerg1, Skp2, and Frzb based on PCA factor, diet, and sex. Expression of each of these is cis-regulated, significantly correlated with the corresponding PCA factor, and previously reported to regulate iron, directly or indirectly. We propose that polymorphisms in multiple genes underlie individual differences in iron regulation, especially in response to dietary iron challenge. This research shows that iron management is a highly complex trait, influenced by multiple genes. Systems genetics analysis of iron homeostasis holds promise for developing new methods for prevention and treatment of iron deficiency anemia and related diseases.

Genetic analysis of iron-deficiency effects on the mouse spleen

Iron homeostasis is crucial to many biological functions in nearly all organisms, with roles ranging from oxygen transport to immune function. Disruption of iron homeostasis may result in iron overload or iron deficiency. Iron deficiency may have severe consequences, including anemia or changes in immune or neurotransmitter systems. Here we report on the variability of phenotypic iron tissue loss and splenomegaly and the associated quantitative trait loci (QTLs), polymorphic areas in the mouse genome that may contain one or more genes that play a role in spleen iron concentration or spleen weight under each dietary treatment. Mice from 26 BXD/Ty recombinant inbred strains, including the parent C57BL/6 and DBA/2 strains, were randomly assigned to adequate iron or iron-deficient diets at weaning. After 120 days, splenomegaly was measured by spleen weight, and spleen iron was assessed using a modified spectrophotometry technique. QTL analyses and gene expression comparisons were then conducted using the WebQTL GeneNetwork. We observed wide, genetic-based variability in splenomegaly and spleen iron loss in BXD/Ty recombinant inbred strains fed an iron-deficient diet. Moreover, we identified several suggestive QTLs. Matching our QTLs with gene expression data from the spleen revealed candidate genes. Our work shows that individual differences in splenomegaly response to iron deficiency are influenced at least partly by genetic constitution. We propose mechanistic hypotheses by which splenomegaly may result from iron deficiency.

Systems genetics of mineral metabolism

Minerals are essential and toxic elements that have an impact on human health. Although we have learned a tremendous amount about the metabolism, biological roles, and health effects of minerals with the tools of biochemistry, cell biology, and molecular genetics, there are gaps in our knowledge of mineral biology that will benefit from new approaches. Forward genetics, whereby variations in phenotypes are mapped to natural genetic variation in the genome, has been successfully used to increase our understanding of many biologically important traits but has not yet been used extensively for mineral metabolism. In addition, the well-appreciated existence of interactions between minerals justifies a broader, systems approach to the study of mineral metabolism, i.e., ionomics. This short review will explain the value of forward genetics and ionomics as tools for exploring mammalian mineral metabolism.

In silico QTL mapping of basal liver iron levels in inbred mouse strains

Both iron deficiency and iron excess are detrimental in many organisms, and previous studies in both mice and humans suggest that genetic variation may influence iron status in mammals. However, these genetic factors are not well defined. To address this issue, we measured basal liver iron levels in 18 inbred strains of mice of both sexes on a defined iron diet and found ∼4-fold variation in liver iron in males (lowest 153 μg/g, highest 661 μg/g) and ∼3-fold variation in females (lowest 222 μg/g, highest 658 μg/g). We carried out a genome-wide association mapping to identify haplotypes underlying differences in liver iron and three other related traits (copper and zinc liver levels, and plasma diferric transferrin levels) in a subset of 14 inbred strains for which genotype information was available. We identified two putative quantitative trait loci (QTL) that contain genes with a known role in iron metabolism: Eif2ak1 and Igf2r. We also identified four putative QTL that reside in previously identified iron-related QTL and 22 novel putative QTL. The most promising putative QTL include a 0.22 Mb region on Chromosome 7 and a 0.32 Mb region on Chromosome 11 that both contain only one candidate gene, Adam12 and Gria1, respectively. Identified putative QTL are good candidates for further refinement and subsequent functional studies.

Towards a unifying, systems biology understanding of large-scale cellular death and destruction caused by poorly liganded iron: Parkinson's, Huntington's, Alzheimer's, prions, bactericides, chemical toxicology and others as examples

Exposure to a variety of toxins and/or infectious agents leads to disease, degeneration and death, often characterised by circumstances in which cells or tissues do not merely die and cease to function but may be more or less entirely obliterated. It is then legitimate to ask the question as to whether, despite the many kinds of agent involved, there may be at least some unifying mechanisms of such cell death and destruction. I summarise the evidence that in a great many cases, one underlying mechanism, providing major stresses of this type, entails continuing and autocatalytic production (based on positive feedback mechanisms) of hydroxyl radicals via Fenton chemistry involving poorly liganded iron, leading to cell death via apoptosis (probably including via pathways induced by changes in the NF-κB system). While every pathway is in some sense connected to every other one, I highlight the literature evidence suggesting that the degenerative effects of many diseases and toxicological insults converge on iron dysregulation. This highlights specifically the role of iron metabolism, and the detailed speciation of iron, in chemical and other toxicology, and has significant implications for the use of iron chelating substances (probably in partnership with appropriate anti-oxidants) as nutritional or therapeutic agents in inhibiting both the progression of these mainly degenerative diseases and the sequelae of both chronic and acute toxin exposure. The complexity of biochemical networks, especially those involving autocatalytic behaviour and positive feedbacks, means that multiple interventions (e.g. of iron chelators plus antioxidants) are likely to prove most effective. A variety of systems biology approaches, that I summarise, can predict both the mechanisms involved in these cell death pathways and the optimal sites of action for nutritional or pharmacological interventions.

Systems genetics analysis of iron regulation in the brain

Iron imbalances in the brain, including excess accumulation and deficiency, are associated with neurological disease and dysfunction; yet, their origins are poorly understood. Using systems genetics analysis, we have learned that large individual differences exist in brain iron concentrations, even in the absence of neurological disease. Much of the individual differences can be tied to the genetic makeup of the individual. This genetic-based differential regulation can be modeled in genetic reference populations of rodents. The work in our laboratory centers on iron regulation in the brain and our animal model consists of 25 BXD/Ty recombinant inbred mouse strains. By studying naturally occurring variation in iron phenotypes, such as tissue iron concentration, we can tie that variability to one or more genes by way of quantitative trait loci (QTL) analysis. Moreover, we can conduct genetic correlation analyses between our phenotypes and others previously measured in the BXD/Ty strains. We have observed several suggestive QTL related to ventral midbrain iron content, including one on chromosome 17 that contains btbd9, a gene that in humans has been associated with restless legs syndrome and serum ferritin. We have also observed gene expression correlations with ventral midbrain iron, including btbd9 expression and dopamine receptor expression. In addition, we have observed significant correlations between ventral midbrain iron content and dopamine-related phenotypes. The following is a discussion of iron regulation in the brain and the contributions a systems genetics approach can make toward understanding the genetic underpinnings and relation to neurological disease.

Iron deficiency alters the day-night variation in monoamine levels in mice

Monoamine metabolism in the central nervous system is altered by dietary iron deficiency, with a stronger effect seen during the active than rest span of the circadian cycle. In this report, we examined changes in intracellular and extracellular monoamine levels, synthetic enzymes, transporter and receptor densities, and responses to amphetamine-induced dopamine (DA) efflux in iron-deficient and iron-sufficient mice. Extracellular striatal DA levels were 15-20% higher in all groups during the active dark phase compared to the inactive light phase, with correspondingly lower dopamine transporter (DAT) and higher tyrosine hydroxylase levels. Iron deficiency decreased DAT density by 20% and 28% in the light and dark phases, respectively, and elevated the DOPAC/DA ratio only in the dark, indicating that iron deficiency does interact with the normal diurnal cues for cyclicity. Enhanced DA efflux after amphetamine stimulation indicates no limitation on monoamine synthesis and release and is consistent with altered synaptic efficacy and perhaps recycling of DA in iron deficiency. These experimental findings provide new evidence that brain iron insufficiency does have a differential effect on the DA system at different biological times of the day and night and may be causally related to the phasic motor symptoms observed in Restless Legs Syndrome.

Genetic dissection of the mouse brain using high-field magnetic resonance microscopy

Magnetic resonance (MR) imaging has demonstrated that variation in brain structure is associated with differences in behavior and disease state. However, it has rarely been practical to prospectively test causal models that link anatomical and functional differences in humans. In the present study we have combined classical mouse genetics with high-field MR to systematically explore and test such structure-functional relations across multiple brain regions. We segmented 33 regions in two parental strains-C57BL/6J (B) and DBA/2J (D)-and in nine BXD recombinant inbred strains. All strains have been studied extensively for more than 20 years using a battery of genetic, functional, anatomical, and behavioral assays. We compared levels of variation within and between strains and sexes, by region, and by system. Average within-strain variation had a coefficient of variation (CV) of 1.6% for the whole brain; while the CV ranged from 2.3 to 3.6% for olfactory bulbs, cortex and cerebellum, and up to approximately 18% for septum and laterodorsal thalamic nucleus. Variation among strain averages ranged from 6.7% for cerebellum, 7.6% for whole brain, 9.0% for cortex, up to approximately 26% for the ventricles, laterodorsal thalamic nucleus, and the interpeduncular nucleus. Heritabilities averaged 0.60+/-0.18. Sex differences were not significant with the possible (and unexpected) exception of the pons ( approximately 20% larger in males). A correlation matrix of regional volumes revealed high correlations among functionally related parts of the CNS (e.g., components of the limbic system), and several high correlations between regions that are not anatomically connected, but that may nonetheless be functionally or genetically coupled.

Genetic modulation of striatal volume by loci on Chrs 6 and 17 in BXD recombinant inbred mice

Natural variation in the absolute and relative size of different parts of the human brain is substantial, with a range that often exceeds a factor of 2. Much of this variation is generated by the cumulative effects of sets of unknown gene variants that modulate the proliferation, growth and death of neurons and glial cells. Discovering and testing the functions of these genes should contribute significantly to our understanding of differences in brain development, behavior and disease susceptibility. We have exploited a large population of genetically well-characterized strains of mice (BXD recombinant inbred strains) to map gene variants that influence the volume of the dorsal striatum (caudate-putamen without nucleus accumbens). We used unbiased methods to estimate volumes bilaterally in a sex-balanced sample taken from the Mouse Brain Library (www.mbl.org). We generated a matched microarray data set to efficiently evaluate candidate genes (www.genenetwork.org). As in humans, volume of the striatum is highly heritable, with greater than twofold differences among strains. We mapped a locus that modulates striatal volume on chromosome (Chr) 6 at 88 +/- 5 Mb. We also uncovered an epistatic interaction between loci on Chr 6 and Chr 17 that modulates striatal volume. Using bioinformatic tools and the corresponding expression database, we have identified positional candidates in these quantitative trait locus intervals.

Sleep and neurofunctions throughout child development: lasting effects of early iron deficiency

Iron-deficiency anemia (IDA) continues to be the most common single nutrient deficiency in the world. Infants are at particular risk due to rapid growth and limited dietary sources of iron. An estimated 20% to 25% of the world's infants have IDA, with at least as many having iron deficiency without anemia. High prevalence is found primarily in developing countries, but also among poor, minority, and immigrant groups in developed ones. Infants with IDA test lower in mental and motor development assessments and show affective differences. After iron therapy, follow-up studies point to long-lasting differences in several domains. Neurofunctional studies showed slower neural transmission in the auditory system despite 1 year of iron therapy in IDA infants; they still had slower transmission in both the auditory and visual systems at preschool age. Different motor activity patterning in all sleep-waking states and several differences in sleep states organization were reported. Persistent sleep and neurofunctional effects could contribute to reduced potential for optimal behavioral and cognitive outcomes in children with a history of IDA.

Iron behaving badly: inappropriate iron chelation as a major contributor to the aetiology of vascular and other progressive inflammatory and degenerative diseases

BACKGROUND

The production of peroxide and superoxide is an inevitable consequence of aerobic metabolism, and while these particular 'reactive oxygen species' (ROSs) can exhibit a number of biological effects, they are not of themselves excessively reactive and thus they are not especially damaging at physiological concentrations. However, their reactions with poorly liganded iron species can lead to the catalytic production of the very reactive and dangerous hydroxyl radical, which is exceptionally damaging, and a major cause of chronic inflammation.

REVIEW

We review the considerable and wide-ranging evidence for the involvement of this combination of (su)peroxide and poorly liganded iron in a large number of physiological and indeed pathological processes and inflammatory disorders, especially those involving the progressive degradation of cellular and organismal performance. These diseases share a great many similarities and thus might be considered to have a common cause (i.e. iron-catalysed free radical and especially hydroxyl radical generation).The studies reviewed include those focused on a series of cardiovascular, metabolic and neurological diseases, where iron can be found at the sites of plaques and lesions, as well as studies showing the significance of iron to aging and longevity. The effective chelation of iron by natural or synthetic ligands is thus of major physiological (and potentially therapeutic) importance. As systems properties, we need to recognise that physiological observables have multiple molecular causes, and studying them in isolation leads to inconsistent patterns of apparent causality when it is the simultaneous combination of multiple factors that is responsible.This explains, for instance, the decidedly mixed effects of antioxidants that have been observed, since in some circumstances (especially the presence of poorly liganded iron) molecules that are nominally antioxidants can actually act as pro-oxidants. The reduction of redox stress thus requires suitable levels of both antioxidants and effective iron chelators. Some polyphenolic antioxidants may serve both roles.Understanding the exact speciation and liganding of iron in all its states is thus crucial to separating its various pro- and anti-inflammatory activities. Redox stress, innate immunity and pro- (and some anti-)inflammatory cytokines are linked in particular via signalling pathways involving NF-kappaB and p38, with the oxidative roles of iron here seemingly involved upstream of the IkappaB kinase (IKK) reaction. In a number of cases it is possible to identify mechanisms by which ROSs and poorly liganded iron act synergistically and autocatalytically, leading to 'runaway' reactions that are hard to control unless one tackles multiple sites of action simultaneously. Some molecules such as statins and erythropoietin, not traditionally associated with anti-inflammatory activity, do indeed have 'pleiotropic' anti-inflammatory effects that may be of benefit here.

CONCLUSION

Overall we argue, by synthesising a widely dispersed literature, that the role of poorly liganded iron has been rather underappreciated in the past, and that in combination with peroxide and superoxide its activity underpins the behaviour of a great many physiological processes that degrade over time. Understanding these requires an integrative, systems-level approach that may lead to novel therapeutic targets.

Diurnal cycle influences peripheral and brain iron levels in mice

Iron movement between organ pools involves a dynamic equilibrium of iron efflux and uptake, and homeostatic mechanisms are likely involved in providing iron to cells and organs when required. Daily iron levels in the plasma pool fluctuate with the diurnal cycle, but clear explanations regarding the objectives and regulation of the flux are lacking. The association between diurnal cycle and iron flux is relevant in the disease of restless legs syndrome (RLS), where individuals display diurnal deficits in motor control, have impaired brain iron metabolism, and perhaps altered iron uptake from the plasma pool. The goal of the present study was to examine diurnal variations in peripheral and regional brain iron to evaluate iron flux between organs in iron-sufficient and iron-deficient mice. In mice fed control diet, liver iron was elevated 30-40%, and plasma iron was reduced 20-30% in the active dark period compared with the inactive light phase. Dietary iron deficiency eliminated this variation in liver iron in male and female mice and in plasma iron in male mice. Reductions in ventral midbrain and nucleus accumbens iron and ferritin were apparent in iron-deficient mice during both diurnal phases, but only during the light phase was an approximately 25% reduction in whole brain iron observed, suggesting different brain iron requirements between phases. These data demonstrate that iron flux between organs is sensitive to diurnal regulatory biology. Importantly, variations in brain iron may have temporal implications regarding neural functioning and may contribute to the diurnal cycle-dependent symptoms of RLS.

Altered iron metabolism in lymphocytes from subjects with restless legs syndrome

OBJECTIVE

Studies using cerebrospinal fluid, magnetic resonance imaging, and autopsy tissue have implicated a primary role for brain iron insufficiency in restless legs syndrome (RLS). If the abnormalities of brain iron regulation reflect a basic disturbance of iron metabolism, then this might be expressed at least partially in some peripheral systems. Thus the study aim was to determine whether patients with RLS and control subjects show differences in lymphocyte iron regulator proteins.

METHODS

Fasting morning blood samples were used to obtain common serum measures of iron status and to determine lymphocyte iron management proteins. Twenty-four women with early-onset RLS and 25 control women without RLS symptoms were studied.

RESULTS

RLS and control subjects were matched for age, hemoglobin, and serum iron profile. However, transferrin receptor (TfR) and DMT1 (divalent metal transporter 1 protein) levels in lymphocytes were significantly higher for RLS patients than for controls. No significant differences in ferritin subtypes or transferrin levels were found. No significant correlations were found between lymphocyte and serum indices of iron status.

INTERPRETATION

RLS lymphocytes showed an increase in ferroportin, implying increased cellular iron excretion, in the face of increased iron need (increased TfR and DMT1). In the absence of changes in H-ferritin, the findings indicate a balance between input and output with no net iron change but probable overall increase in iron turnover. The lack of any significant correlation between serum and lymphocyte iron indices indicates that iron management proteins from lymphocytes are at a minimum an alternative and independent marker of cellular iron metabolism.