Biomedical subjects

John L Beard

Publications and source records attributed to John L Beard.

At least 19 recordsLinked to original sources

PubMed2007

Early iron deficiency alters sensorimotor development and brain monoamines in rats.

Iron deficiency in human infancy reportedly leads to developmental delays and changes in neurobiology that may be irreversible. Using a rodent model, the present study examined whether dietary iron deficiency late in pregnancy and during lactation alters sensorimotor development and brain monoaminergic systems. Rats were assigned to 1 of 4 dietary treatments during gestation and lactation: 1) iron sufficient control; 2) prenatal iron deficiency beginning on gestational d 15 (G15); 3) postnatal iron deficiency beginning on postnatal d 4 (P4); 4) iron deficiency beginning on G15 followed by an iron sufficient diet on P4. Developmental milestones, open field behavior, brain iron and proteins, monoamines, and their transporters were evaluated between P6 and P21. Only G15 iron deficient rats had greater dopaminergic activity than controls as indicated by increased tyrosine hydroxylase levels, phosphorylated tyrosine hydroxylase levels, and cellular dopamine in prefrontal cortex and striatum at P15. These rats also showed delayed eye opening, ear development, and reduced locomotor activity. Iron repletion at P4 returned most measures to control levels by the time of weaning. Postnatal iron deficiency reduced striatal and ventral midbrain iron as well as cellular dopamine levels in prefrontal cortex and striatum at P21. Developmental delays in ear development and achievement in bar holding and surface righting also resulted from postnatal iron deficiency. These results indicate that iron deficiency begun at G15 affects early dopamine neurobiology, the development of specific developmental milestones, and behavior in preweaned rats.

Aging↗

PubMed2007

Down-regulation of dopamine transporter by iron chelation in vitro is mediated by altered trafficking, not synthesis.

Neurological development and functioning of dopamine (DA) neurotransmission is adversely affected by iron deficiency in early life. Iron-deficient rats demonstrate significant elevations in extracellular DA and a reduction in dopamine transporter (DAT) densities in the caudate putamen and nucleus accumbens. To explore possible mechanisms by which cellular iron concentrations control DAT functioning, endogenous DAT-expressing PC12 cells were used to determine the effect of iron chelation on DAT protein and mRNA expression patterns. In addition, we used human DAT (hDAT)-transfected Neuro2a (N2A) cells to examine DAT degradation and trafficking patterns. A 50 microM treatment for 24 h with the iron chelator, desferrioxamine (DFO), significantly decreased dopamine uptake in a dose-dependent manner, with no apparent change in K(m), in both PC12 and N2A cells. Reduced DA uptake was accompanied by concentration- and time-dependent reductions in total DAT protein levels in both cell lines. Exposure to increasing concentrations of DFO did not significantly alter DAT mRNA in either PC12 or N2A cells. However, DAT degradation rates increased three-fivefold in both cell types exposed to 50 microM DFO for 24 h. Biotinylation studies in N2A cells indicate a more dramatic loss of DAT in the membrane fraction, while OptiPrep fractionation experiments revealed an increase in lysosomal DAT with iron chelation. Inhibition of protein kinase C activation with staurosporin prevented the effect of iron chelation on DAT function, suggesting that in vitro iron chelation affects DAT primarily through the effects on trafficking rather than on synthesis.

Animals↗

PubMed2006

Acoustic startle response is disrupted in iron-deficient rats.

Diurnal effects on motor control are evident in the human disease of Restless Leg Syndrome (RLS), which is purported to be linked to brain iron deficiency as well as alterations in dopaminergic systems. Thus, we explored the relationship between daily rhythms, the onset of motor dysregulation and brain iron deficiency in an animal model of iron deficiency. Male and female weanling Sprague-Dawley rats consuming control (CN) or iron-deficient (ID) diets were examined weekly for acoustic startle response (ASR) and prepulse inhibition (PPI) for a 5-week period. Iron deficiency reduced the magnitude, but not timing, of the ASR at specific time points. ASR was elevated 60% at the onset of the dark cycle relative to the median of the light cycle in male CN and ID rats. The respective elevation was 400% and 150% in female CN and ID rats during the first 2 weeks of testing. The diurnal cycle of ASR response was attenuated by 3 weeks of testing in both dietary treatment groups. PPI was not affected by iron deficiency, sex, diurnal cycle or the interaction between these factors. These results thus demonstrate that iron deficiency moderately alters ASR signaling although the inhibitory pathways of ASR do not appear to be affected.

Acoustic Stimulation↗

PubMed2006

Persistent neurochemical and behavioral abnormalities in adulthood despite early iron supplementation for perinatal iron deficiency anemia in rats.

BACKGROUND: Iron deficiency anemia (IDA) has been associated with altered cognitive, motor, and social-emotional outcomes in human infants. We recently reported that rats with chronic perinatal IDA, had altered regional brain iron, monoamines, and sensorimotor skill emergence during early development. OBJECTIVE: To examine the long-term consequences of chronic perinatal IDA on behavior, brain iron and monoamine systems after dietary iron treatment in rats. METHODS: Sixty dams were randomly assigned to iron-sufficient (CN) or low-iron (EID) diets during gestation and lactation. Thereafter, all offspring were fed the iron-sufficient diet, assessed for hematology and behavior after weaning and into adulthood and for brain measures as adults (regional brain iron, monoamines, dopamine and serotonin transporters, and dopamine receptor). Behavioral assessments included sensorimotor function, general activity, response to novelty, spatial alternation, and spatial water maze performance. RESULTS: Hematology and growth were similar for EID and CN rats by postnatal day 35. In adulthood, EID thalamic iron content was lower. Monoamines, dopamine transporter, and dopamine receptor concentrations did not differ from CN. EID serotonin transporter concentration was reduced in striatum and related regions. EID rats had persisting sensorimotor deficits (delayed vibrissae-evoked forelimb placing, longer sticker removal time, and more imperfect grooming chains), were more hesitant in novel settings, and had poorer spatial water maze performance than CN. General activity and spatial alternation were similar for EID and CN. CONCLUSION: Rats that had chronic perinatal IDA showed behavioral impairments that suggest persistent striatal dopamine and hippocampal dysfunction despite normalization of hematology, growth and most brain measures.

Anemia, Iron-Deficiency↗

PubMed2006

Cellular iron concentrations directly affect the expression levels of norepinephrine transporter in PC12 cells and rat brain tissue.

Neurological development and functioning are adversely affected by iron deficiency in early life. Iron-deficient rats are known to have elevations in extracellular DA and NE, suggesting alterations in reuptake of these monoamines. To explore possible mechanisms by which cellular iron concentrations may alter NE transporter functioning, we utilized NET expressing PC12 cells and iron-deficient rats to explore the relationship between NET protein and mRNA expression patterns and iron concentrations. Treatment of PC12 with the iron chelator, desferrioxamine mesylate (DFO, 50 microM for 24 h), significantly decreased [3H] NE uptake by more than 35% with no apparent change in Km. PC12 cells exposed to increasing concentrations of DFO (25-100 microM) exhibited a dose response decrease in [3H] NE uptake within 24 h (38-73% of control) that paralleled a decrease in cellular NET protein content. Inhibition of protein synthesis with cycloheximide resulted in NET disappearance rates from DFO-treated cells greatly exceeding the rate of loss from control cells. RT-PCR analysis revealed only a modest decrease in NET mRNA levels. Rat brain locus ceruleus and thalamus NET mRNA levels were also only modestly decreased (10-15%) despite a 40% reduction in regional brain iron. In contrast, NET proteins levels in thalamus and locus ceruleus were strongly affected by regional iron deficiency with high correlations with iron concentrations (r > 0.94 and r > 0.80 respectively). The present findings demonstrate that NET protein concentrations and functioning are dramatically reduced with iron deficiency; the modest effect on mRNA levels suggests a stronger influence on NET trafficking and degradation than on protein synthesis.

Animals↗

PubMed2006

Iron deficiency affects acoustic startle response and latency, but not prepulse inhibition in young adult rats.

Iron deficiency is associated with alterations in dopamine and serotonin transporters as well as changes in dopamine receptor (DR) density, monoamine concentrations, and in vivo extracellular contents of monoamines in terminal fields. Human infants with iron deficiency have both delayed maturation as well as lengthened central conduction times in auditory evoked potential studies. The current study utilizes the magnitude of the acoustic startle response (ASR), prepulse inhibition (PPI), and mean latency to maximum startle response (T(max)), to examine the functional integrity of response to environmental cues. Male and female rats consumed iron deficient (ID) or iron adequate (CN) diets from weaning until adulthood. ID rats of both sexes had 20-60% reductions in ASR when compared to CN rats but there was no effect on PPI. T(max) was significantly longer by 10-20% in females, but not males. Dopamine transporter density was significantly lower in putamen, nucleus accumbens, and olfactory tubercle in males, but not female rats while the serotonin transporter was significantly different from control animal density in five of 14 brain regions. Norepinephrine transporter density was lower in the locus ceruleus of ID male rats but was unaffected in ID female rats. Regression modeling of ASR with brain monoamine transporters and receptors showed hematocrit, norepinephrine transporter (NET) in dentate gyrus, and D1R in the nucleus accumbens account for nearly 49% of the variance in ASR. T(max) was not significantly associated with any of the independent variables. We conclude that iron deficiency affects the startle response, but not the inhibitory circuits involved in prepulse inhibition. Importantly, sex also strongly influenced these behavioral responses. Future studies, perhaps pharmacologic in nature, are necessary to ascertain whether iron deficiency modifies the contribution of monoaminergic systems to responses to environmental stimuli.

Acoustic Stimulation↗

PubMed2006

Moderate iron deficiency in infancy: biology and behavior in young rats.

Iron deficiency anemia in early childhood is associated with developmental delays and perhaps, irreversible alterations in neurological functioning. The goals were to determine if dietary induced gestational and lactational iron deficiency alters brain monoamine metabolism and behaviors dependent on that neurotransmitter system. Young pregnant rats were provided iron deficient or control diets from early in gestation through to weaning of pups and brain iron concentration, regional monoamine variables and achievement of specific developmental milestones were determined throughout lactation. Despite anemia during lactation, most brain iron concentrations did not fall significantly until P25, and well after significant changes in monoamine levels, transporter levels, and D2R density changed in terminal fields. The changes in D2R density were far smaller than previously observed models that utilized severe dietary restriction during lactation or after weaning. Iron deficient pups had normal birth weight, but were delayed in the attainment of a number of milestones (bar holding, vibrissae-evoked forelimb placing). This approach of iron deficiency in utero and during lactation sufficient to cause moderate anemia but not stunt growth demonstrates that monaminergic metabolism changes occur prior to profound declines in brain iron concentration and is associated with developmental delays. Similar developmental delays in iron deficient human infants suggest to us that alterations in iron status during this developmental period likely affects developing brain monaminergic systems in these infants.

Age Factors↗

PubMed2006

Ferritin subunits in CSF are decreased in restless legs syndrome.

Restless legs syndrome (RLS) is a neurological disorder that may be related to iron misregulation at the level of the central nervous system. Evidence that iron is involved in RLS comes from magnetic resonance imaging data, autopsy studies, analyses of cerebrospinal fluid (CSF), and correlations of symptoms with serum ferritin. To further examine the possibility that brain iron status is insufficient in RLS, we determined ferritin levels in the CSF. Specifically, we differentiated between the H- and L-subunits of ferritin, because these peptides are expressed from different chromosomes and have different functions. We measured H- and L-ferritin subunit levels in control and RLS human CSF using immunoblot analysis and found that both H- and L-ferritin are significantly decreased in early but not late-onset RLS. Additionally, we quantified total protein in each CSF sample to establish that the decrease in ferritin subunits in RLS did not reflect a decrease in total protein in CSF. Furthermore, we used equal amounts of total CSF protein in the immunoblot analyses, in contrast to previously published studies that provided only volumetric data, to determine which approach was more accurate for quantifying the amount of ferritin relative to other proteins in CSF. Our results establish a protein standard in RLS, provide a comparative analysis of protein-controlled versus volumetric immunoblot techniques, and argue for a profound loss of iron storage capacity in the brain in RLS, specifically in the early onset RLS phenotype. These data suggest that CSF ferritin levels may provide a biomarker for assisting in the diagnosis of RLS.

Age of Onset↗

PubMed2006

Iron bioavailability: UK Food Standards Agency workshop report.

The UK Food Standards Agency convened a group of expert scientists to review current research investigating factors affecting iron status and the bioavailability of dietary iron. Results presented at the workshop show menstrual blood loss to be the major determinant of body iron stores in premenopausal women. In the presence of abundant and varied food supplies, the health consequences of lower iron bioavailability are unclear and require further investigation.

Biological Availability↗

PubMed2006

Diet-induced iron deficiency anemia and pregnancy outcome in rhesus monkeys.

BACKGROUND: Iron deficiency anemia (IDA) is relatively common in the third trimester of pregnancy, but causal associations with low birth weight and compromised neonatal iron status are difficult to establish in human populations. OBJECTIVE: The objective was to determine the effects of diet-induced IDA on intrauterine growth and neonatal iron status in an appropriate animal model for third-trimester IDA in women. DESIGN: Hematologic and iron-status measures, pregnancy outcomes, and fetal and neonatal evaluations were compared between pregnant rhesus monkeys (n = 14) fed a diet containing 10 microg Fe/g diet from the time of pregnancy detection (gestation days 28-30) and controls (n = 24) fed 100 microg Fe/g diet. RESULTS: By the third trimester, 79% of the iron-deprived dams and 29% of the control monkeys had a hemoglobin concentration <11 g/dL. There were also significant group differences in hematocrit, mean corpuscular volume, transferrin saturation, serum ferritin, and serum iron. At birth, the newborns of monkeys iron-deprived during pregnancy had significantly lower hemoglobin, mean corpuscular volume, and mean corpuscular hemoglobin values and a lower ratio of erythroid to total colony-forming units in bone marrow than did the control newborns. Pregnancy weight gain did not differ significantly between the iron-deprived and control dams, and the fetuses and newborns of the iron-deprived dams were not growth retarded relative to the controls. Gestation length, the number of stillbirths, and neonatal neurobehavioral test scores did not differ significantly by diet group. CONCLUSION: These data indicate that an inadequate intake of iron from the diet during pregnancy in rhesus monkeys can lead to compromised hematologic status of the neonate without indications of growth retardation or impaired neurologic function at birth.

Anemia, Iron-Deficiency↗

PubMed2006

Interpretation of serum ferritin concentrations as indicators of total-body iron stores in survey populations: the role of biomarkers for the acute phase response.

BACKGROUND: Nutritional surveys use acute phase protein (APP) biomarkers such as C-reactive protein (CRP) and alpha1-acid glycoprotein (AGP) to identify the influence of inflammation on the distribution of iron status biomarkers. Few, however, have examined which biomarker better identifies persons with spurious elevations in iron status markers. OBJECTIVE: We explored the relations of APP biomarkers to iron-status biomarkers in infants and school-age children. DESIGN: In screening surveys, we identified a sample of African American infants (n = 351) and Guatemalan school-age children (n = 375). We used a common set of APP and iron-status biomarkers to examine the association between the 2 sets of markers (laboratory variables). RESULTS: The overall prevalence of either inflammation or iron deficiency was <10% in both samples. The log AGP and CRP values were significantly correlated (r = 0.70), but the unexplained variance still was >50%. Serum ferritin-but not transferrin receptor, transferrin receptor index, or serum iron-was related to APP concentrations, but poor positive predictive value (<72%) and low kappa scores were found. Ferritin concentrations >1 geometric SD above the geometric mean were poorly predicted by either elevated AGP or CRP. Qualitative CRP analysis was not effective in identifying persons who had other indications of mild inflammation. CONCLUSIONS: These analyses show that a low prevalence of inflammation has little influence on the distribution of ferritin, and 2 common indicators of inflammation do not perform equally well in identifying persons who may have elevations in ferritin due to inflammation.

Acute-Phase Proteins↗

PubMed2005

Iron deficiency: differential effects on monoamine transporters.

In this study, we extend previous work on iron deficiency and dopamine (DA) transporters to include an examination of central serotonin (5-HT) and noradrenergic (NE) transporters. Rats were fed either iron deficient (ID) or iron adequate (CN) diets from weaning until adulthood. In males, an additional group of iron deficient animals (IR) were given iron supplementation. DA, 5-HT, and NE transporter binding was done in situ on thin sections. ID males, but not females, decreased DA transporter binding in the nucleus accumbens, caudate putamen and substantia nigra by 20-40%. ID males also had a 20-30% reduction in 5-HT transporter binding in several areas (nucleus accumbens, olfactory tubercle, colliculus) while in ID females there was 15-25% increased serotonin transporter binding in the olfactory tubercle, zona incerta, anteroventral thalamic nucleus and vestibular nucleus. Iron deficiency reduced 3H-nisoxetine binding to the NE transporter in locus ceruleus and anteroventral thalamic nucleus in males but not females. Only some of the changes observed in DA, serotonin and NE transporter binding were reversible by iron supplementation. These findings show that iron deficiency affects monoamine systems related to homeostasis and in most cases males appear to be more vulnerable than females.

Animals↗

PubMed2005

Iron-biofortified rice improves the iron stores of nonanemic Filipino women.

Iron deficiency is endemic in much of the world, and food system-based approaches to eradication may be viable with new plant breeding approaches to increase the micronutrient content in staple crops. It is thought that conventional plant breeding approaches provide varieties of rice that have 400-500% higher iron contents than varieties commonly consumed in much of Asia. The efficacy of consuming high-iron rice was tested during a 9-mo feeding trial with a double-blind dietary intervention in 192 religious sisters living in 10 convents around metro Manila, the Philippines. Subjects were randomly assigned to consume either high-iron rice (3.21 mg/kg Fe) or a local variety of control rice (0.57 mg/kg Fe), and daily food consumption was monitored. The high-iron rice contributed 1.79 mg Fe/d to the diet in contrast to 0.37 mg Fe/d from the control rice. The 17% difference in total dietary iron consumption compared with controls (10.16 +/- 1.06 vs. 8.44 +/- 1.82 mg/d) resulted in a modest increase in serum ferritin (P = 0.10) and total body iron (P = 0.06) and no increase in hemoglobin (P = 0.59). However, the response was greater in nonanemic subjects for ferritin (P = 0.02) and body iron (P = 0.05), representing a 20% increase after controlling for baseline values and daily rice consumption. The greatest improvements in iron status were seen in those nonanemic women who had the lowest baseline iron status and in those who consumed the most iron from rice. Consumption of biofortified rice, without any other changes in diet, is efficacious in improving iron stores of women with iron-poor diets in the developing world.

Adult↗

PubMed2005

Maternal iron deficiency anemia affects postpartum emotions and cognition.

The aim of this study was to determine whether iron deficiency anemia (IDA) in mothers alters their maternal cognitive and behavioral performance, the mother-infant interaction, and the infant's development. This article focuses on the relation between IDA and cognition as well as behavioral affect in the young mothers. This prospective, randomized, controlled, intervention trial was conducted in South Africa among 3 groups of mothers: nonanemic controls and anemic mothers receiving either placebo (10 microg folate and 25 mg vitamin C) or daily iron (125 mg FeS0(4), 10 microg folate, 25 mg vitamin C). Mothers of full-term normal birth weight babies were followed from 10 wk to 9 mo postpartum (n = 81). Maternal hematologic and iron status, socioeconomic, cognitive, and emotional status, mother-infant interaction, and the development of the infants were assessed at 10 wk and 9 mo postpartum. Behavioral and cognitive variables at baseline did not differ between iron-deficient anemic mothers and nonanemic mothers. However, iron treatment resulted in a 25% improvement (P < 0.05) in previously iron-deficient mothers' depression and stress scales as well as in the Raven's Progressive Matrices test. Anemic mothers administered placebo did not improve in behavioral measures. Multivariate analysis showed a strong association between iron status variables (hemoglobin, mean corpuscular volume, and transferrin saturation) and cognitive variables (Digit Symbol) as well as behavioral variables (anxiety, stress, depression). This study demonstrates that there is a strong relation between iron status and depression, stress, and cognitive functioning in poor African mothers during the postpartum period. There are likely ramifications of this poorer "functioning" on mother-child interactions and infant development, but the constraints around this relation will have to be defined in larger studies.

Adult↗

PubMed2005

Mother-infant interactions and infant development are altered by maternal iron deficiency anemia.

The aim of this study was to determine whether iron deficiency anemia (IDA) in young South African mothers alters mother-infant interactions and the infant's development. The study was a prospective, randomized, controlled intervention trial with 3 groups of mothers: nonanemic controls and anemic mothers administered either placebo (25 mg ascorbic acid and 10 microg folate) or daily iron treatment (125 mg FeSO(4) plus ascorbate and folate). Mothers of full-term, normal birth weight infants (n = 81) were followed from 10 wk to 9 mo postpartum. Maternal iron status, socioeconomic level, mother-infant interaction [Parent/Caregiver Involvement Scale (PCIS scale)], and infant development (Griffiths scale) were assessed. At baseline, anemic mothers tended (P < 0.10) to be less responsive to, and more controlling of, their infants. Infants of anemic mothers were developmentally delayed at 10 wk in hand-eye movement and overall quotient. Despite normalization of maternal iron status with supplementation in some mothers, the developmental delays were not diminished at 9 mo. At 9 mo, anemic mothers were significantly more "negative" towards their babies, engaged less in goal setting, and were less "responsive" than control mothers. In contrast, the behavior of anemic mothers given iron treatment toward their children was similar to that of the control mothers on all 11 scales of the PCIS. In conclusion, IDA altered mother-child interactions at both 10 wk and 9 mo postpartum. Additionally, infants whose mothers were anemic in the early postpartum scored worse on developmental tests at 10 wk and 9 mo of age.

Anemia, Iron-Deficiency↗

PubMed2005

Hemoglobin and ferritin are currently the most efficient indicators of population response to iron interventions: an analysis of nine randomized controlled trials.

Governments and donor agencies have implemented pilot and large-scale iron fortification programs, but there has been no consensus on the best choice of indicators to monitor population response to these interventions. We analyzed data from 9 randomized iron intervention trials to determine which of the following indicator(s) of iron status show the largest response in a population: hemoglobin (Hb), ferritin, transferrin receptor (TfR), zinc protoporphyrin (ZPP), mean cell volume (MCV), transferrin saturation (TS), and total body-iron store. We expressed the change in each indicator in response to the iron intervention in SD units (SDU) for the intervention group compared with the control group. Ferritin increased by > or =0.2 SDU in all trials and was significant in 7. Hb changed by > or =0.2 SDU in 6 and was significant in 5. TfR increased by > or =0.2 SDU in 5 of 8 interventions in which it was measured and was significant in 4. ZPP increased by > or =0.2 SDU and was significant in 3 of 6 interventions. Excluding Hb, the indicator with the largest change in SDU was ferritin in 4 trials, TS in 2 trials, body-iron store in 2 trials, and TfR in 1. In the 2 cases in which body-iron stores showed the largest change, the change in ferritin was nearly as large. Our results suggest that with currently available technologies, ferritin shows larger and more consistent response to iron interventions than ZPP or TfR. We cannot make confident inference about MCV or TS, which were included in only 4 and 2 trials, respectively. It is possible that the optimal indicator(s) may differ with age, sex, and pregnancy. There were too few trials in each age and sex group to allow us to explore this question.

Adolescent↗

PubMed2005

Ferritin levels in the cerebrospinal fluid and restless legs syndrome: effects of different clinical phenotypes.

STUDY OBJECTIVE: To determine whether patients with restless legs syndrome (RLS) and controls differ in regard to levels of ferritin and transferrin in the cerebrospinal fluid (CSF) when samples are collected at night, to determine whether patients with early-onset and late-onset RLS show a different outcome for CSF values, and to determine whether the CSF ferritin level correlates with disease severity. DESIGN: Collection of CSF and plasma; assessment of disease severity using objective (periodic limb movements) and subjective (Johns Hopkins Restless Legs Severity Scale) measures of severity. SETTING: General Clinical Research Center. PARTICIPANTS: Thirty subjects with idiopathic RLS (15 early- and 15 late-onset RLS) and 22 age- and sex-matched controls. INTERVENTION: N/A. RESULTS: Nighttime CSF ferritin levels were lower in the total RLS group compared with controls. Further assessment found that the early-onset (less than 45 years of age) but not the late-onset (greater than or equal to 45 years of age) RLS group had significantly lower CSF ferritin levels compared with controls. There was a strong correlation between the age of symptom onset and CSF ferritin values (r = 0.64): the earlier the age, the lower the ferritin level. A regression analysis showed that both sex and RLS subtype had significant effects on the CSF ferritin level, with women with early-onset RLS having substantial lower values than men with late-onset RLS. A comparison between these nighttime CSF values and previously published daytime samples suggests that diurnal changes may have effects on the findings. CONCLUSIONS: This study is distinct in showing that the degree of the CSF-ferritin effect is best defined by the clinical phenotypes of sex and age of symptom onset and by the time of day that samples are collected.

Adult↗

PubMed2004

Interactions and reactions of ferritin with DNA.

Ferritin, normally considered a cytoplasmic iron-storage protein, is also found in the nuclei of some cells. There is no current agreement about its function(s) in this environment. Proposals include DNA protection, provision of iron to nuclear enzymes, and regulation of transcription initiation, but evidence for these functions is scanty. We have shown previously that H-ferritin subunits can be cross-linked to chromosomal DNA in vivo (Thompson, K. J., Fried, M. G., Ye, Z., Boyer, P., and Connor, J. R. (2002) J. Cell Sci. 115, 2165-2177). Here we describe systematic analyses of DNA binding and the covalent stability of DNA in the presence of ferritins from several different sources. Our data show that the H-subunit of human ferritin binds DNA, whereas neither the L-subunit nor the ferroxidase-deficient 222-mutant of the H-subunit has detectable binding activity. DNA binding is without significant preference for base composition, sequence, or the nature of DNA ends. H- and L-ferritins and ferritins of mixed subunit composition stimulate the conversion of superhelical plasmid DNA to the relaxed form. The sensitivity of this conversion to glycerol suggests that DNA is nicked by a free radical mechanism. The rate of nicking correlates with the iron content of the ferritin and is strongly inhibited by chelators. Ferritin-dependent nicking is characterized by a kinetic lag that is not seen in control reactions containing free iron species. These results suggest that the release of iron from ferritin is an important part of the nicking mechanism. The potential role of ferritin as a protector of the genome is discussed in the context of these results.

Buffers↗