Coronary heart disease and iron status: meta-analyses of prospective studies.
BACKGROUND: Studies of iron status and coronary heart disease (CHD) have yielded conflicting results. In a systematic review ("meta-analysis"), we quantitatively assessed epidemiological associations reported in prospective studies. METHODS AND RESULTS: Studies were identified by computer-assisted searches of the published literature, scanning of relevant reference lists, hand searching of relevant journals, and discussions with relevant authors. The following was abstracted: size and type of cohort, mean age, mean duration of follow-up, assay methods, degree of adjustment for confounders, and relationship of CHD risk to the baseline assay results. Twelve studies were identified, involving a total of 7800 CHD cases, with several reporting on >1 marker of iron status. For serum ferritin, with 570 CHD cases in 5 studies, comparison of individuals with baseline values >/=200 versus <200 microg/L yielded a combined risk ratio of 1.0 (95% CI, 0.8 to 1.3). For transferrin saturation, with 6194 CHD cases in 5 studies, comparison of individuals in the top third with those in the bottom third of the baseline measurements yielded a combined risk ratio of 0.9 (95% CI, 0.7 to 1.1). Comparisons of individuals in top and bottom thirds of baseline measurements also yielded nonsignificant risk ratios in combined analyses of studies involving total iron-binding capacity (combined risk ratio, 1.0; 95% CI, 0.7 to 1.5), serum iron (0.8; 95% CI, 0.7 to 1.0), and total dietary iron (0.8; 95% CI, 0.7 to 1.1). CONCLUSIONS: Published prospective studies do not provide good evidence to support the existence of strong epidemiological associations between iron status and CHD. (+info)
The identification of ferritin in the nucleus of K562 cells, and investigation of a possible role in the transcriptional regulation of adult beta-globin gene expression.
We studied the subcellular distribution of ferritin in K562 cells by immunofluorescence techniques and have made a reappraisal of a direct binding interaction between ferritin and the proximal promoter region of the human beta-globin gene, as previously mentioned in the literature. Confocal microscopy indicates that ferritin, the iron-storage protein, is present in the nucleus of K562 cells, in addition to its expected cytoplasmic localisation. The stain distribution suggests that it is not directly associated with the nuclear matrix. Using a gel mobility shift assay, a protein that cross-reacts with monoclonal ferritin antibodies competitively binds to a double-stranded oligonucleotide spanning the region situated 150 base pairs upstream from the beta-globin transcription start site. Despite this antibody cross-reactivity, the protein is unlike cytosolic ferritin as it appears to be highly sensitive to both temperature and freeze-thaw cycles, and UV-crosslinking experiments indicate that the molecular mass of the protein factor lies between 90 and 100 kDa. In conclusion, while the intranuclear location of ferritin is described in the present study, ferritin is not in direct contact with the beta-globin promoter region. (+info)
Ferritin mutants of Escherichia coli are iron deficient and growth impaired, and fur mutants are iron deficient.
Escherichia coli contains at least two iron storage proteins, a ferritin (FtnA) and a bacterioferritin (Bfr). To investigate their specific functions, the corresponding genes (ftnA and bfr) were inactivated by replacing the chromosomal ftnA and bfr genes with disrupted derivatives containing antibiotic resistance cassettes in place of internal segments of the corresponding coding regions. Single mutants (ftnA::spc and bfr::kan) and a double mutant (ftnA::spc bfr::kan) were generated and confirmed by Western and Southern blot analyses. The iron contents of the parental strain (W3110) and the bfr mutant increased by 1.5- to 2-fold during the transition from logarithmic to stationary phase in iron-rich media, whereas the iron contents of the ftnA and ftnA bfr mutants remained unchanged. The ftnA and ftnA bfr mutants were growth impaired in iron-deficient media, but this was apparent only after the mutant and parental strains had been precultured in iron-rich media. Surprisingly, ferric iron uptake regulation (fur) mutants also had very low iron contents (2.5-fold less iron than Fur+ strains) despite constitutive expression of the iron acquisition systems. The iron deficiencies of the ftnA and fur mutants were confirmed by Mossbauer spectroscopy, which further showed that the low iron contents of ftnA mutants are due to a lack of magnetically ordered ferric iron clusters likely to correspond to FtnA iron cores. In combination with the fur mutation, ftnA and bfr mutations produced an enhanced sensitivity to hydroperoxides, presumably due to an increase in production of "reactive ferrous iron." It is concluded that FtnA acts as an iron store accommodating up to 50% of the cellular iron during postexponential growth in iron-rich media and providing a source of iron that partially compensates for iron deficiency during iron-restricted growth. In addition to repressing the iron acquisition systems, Fur appears to regulate the demand for iron, probably by controlling the expression of iron-containing proteins. The role of Bfr remains unclear. (+info)
Ferroxidase activity of ferritin: effects of pH, buffer and Fe(II) and Fe(III) concentrations on Fe(II) autoxidation and ferroxidation.
It is widely accepted that iron deposition in the iron storage protein ferritin in vitro involves Fe(II) oxidation, and that ferritin facilitates this oxidation at a ferroxidase site on the protein. However, these views have recently been questioned, with the protein ferroxidase activity instead being attributed to autoxidation from the buffer alone. Ligand exchange between another protein with ferroxidase activity and ferritin has been proposed as an alternative mechanism for iron incorporation into ferritin. In the present work, a pH stat apparatus is used to eliminate the influence of buffers on iron(II) oxidation. Here we show that the recent experiments questioning the ferroxidase activity of ferritin were flawed by inadequate pH control, that buffers actually retard rather than facilitate iron(II) oxidation, and that horse spleen ferritin has ferroxidase activity when measured under proper experimental conditions. Furthermore, high pH (7.0), a high Fe(II) concentration and the presence of Fe(III) all favour Fe(II) autoxidation in the presence or absence of ferritin. (+info)
Streptavidin facilitates internalization and pulmonary targeting of an anti-endothelial cell antibody (platelet-endothelial cell adhesion molecule 1): a strategy for vascular immunotargeting of drugs.
Conjugation of drugs with antibodies to surface endothelial antigens is a potential strategy for drug delivery to endothelium. We studied antibodies to platelet-endothelial adhesion molecule 1 (PECAM-1, a stably expressed endothelial antigen) as carriers for vascular immunotargeting. Although 125I-labeled anti-PECAM bound to endothelial cells in culture, the antibody was poorly internalized by the cells and accumulated poorly after intravenous administration in mice and rats. However, conjugation of biotinylated anti-PECAM (b-anti-PECAM) with streptavidin (SA) markedly stimulated uptake and internalization of anti-PECAM by endothelial cells and by cells expressing PECAM. In addition, conjugation with streptavidin markedly stimulated uptake of 125I-labeled b-anti-PECAM in perfused rat lungs and in the lungs of intact animals after either intravenous or intraarterial injection. The antioxidant enzyme catalase conjugated with b-anti-PECAM/SA bound to endothelial cells in culture, entered the cells, escaped intracellular degradation, and protected the cells against H2O2-induced injury. Anti-PECAM/SA/125I-catalase accumulated in the lungs after intravenous injection or in the perfused rat lungs and protected these lungs against H2O2-induced injury. Thus, modification of a poor carrier antibody with biotin and SA provides an approach for facilitation of antibody-mediated drug targeting. Anti-PECAM/SA is a promising candidate for vascular immunotargeting of bioactive drugs. (+info)
Transcriptional regulation of the mouse ferritin H gene. Involvement of p300/CBP adaptor proteins in FER-1 enhancer activity.
We previously identified a major enhancer of the mouse ferritin H gene (FER-1) that is central to repression of the ferritin H gene by the adenovirus E1A oncogene (Tsuji, Y., Akebi, N., Lam, T. K., Nakabeppu, Y., Torti, S. V., and Torti, F. M. (1995) Mol. Cell. Biol. 15, 5152-5164). To dissect the molecular mechanism of transcriptional regulation of ferritin H, E1A mutants were tested for their ability to repress FER-1 enhancer activity using cotransfection with ferritin H-chloramphenicol acetyltransferase (CAT) reporter constructs. Here we report that p300/CBP transcriptional adaptor proteins are involved in the regulation of ferritin H transcription through the FER-1 enhancer element. Thus, E1A mutants that failed to bind p300/CBP lost the ability to repress FER-1, whereas mutants of E1A that abrogated its interaction with Rb, p107, or p130 were fully functional in transcriptional repression. Transfection with E1A did not affect endogenous p300/CBP levels, suggesting that repression of FER-1 by E1A is not due to repression of p300/CBP synthesis, but to E1A and p300/CBP interaction. In addition, we have demonstrated that transfection of a p300 expression plasmid significantly activated ferritin H-CAT containing the FER-1 enhancer, but had a marginal effect on ferritin H-CAT with FER-1 deleted. Furthermore, both wild-type p300 and a p300 mutant that failed to bind E1A but retained an adaptor function restored FER-1 enhancer activity repressed by E1A. Sodium butyrate, an inhibitor of histone deacetylase, mimicked p300/CBP function in activation of ferritin H-CAT and elevation of endogenous ferritin H mRNA, suggesting that the histone acetyltransferase activity of p300/CBP or its associated proteins may contribute to the activation of ferritin H transcription. Recruitment of these broadly active transcriptional adaptor proteins for ferritin H synthesis may represent an important mechanism by which changes in iron metabolism are coordinated with other cellular responses mediated by p300/CBP. (+info)
Iron-deficient diet reduces atherosclerotic lesions in apoE-deficient mice.
BACKGROUND: Iron deposition is evident in human atherosclerotic lesions, suggesting that iron may play a role in the development of atherosclerosis. To test this idea, the correlation between the extent of iron deposition and the severity of atherosclerosis in apolipoprotein E (apoE)-deficient mice was investigated. Furthermore, the effect of a low-iron diet on the progression of atherosclerotic lesions in these animals was evaluated. METHODS AND RESULTS: Iron deposition in tissues of apoE-deficient mice was examined by Perls' staining method. The results clearly demonstrated that iron deposits are present in atherosclerotic lesions and tissue sections of heart and liver in an age-dependent manner. When the young mice received a low-iron diet for 3 months, the hematocrit, serum iron, hemoglobin, and cholesterol concentrations were not significantly altered compared with those of littermates placed on a chow diet. However, the serum ferritin level of animals in the iron-restricted group was 27% to 30% lower than that of the control group in either sex. Furthermore, the lipoproteins isolated from the iron-restricted group exhibited greater resistance to copper-induced oxidation. Histological examination revealed that atherosclerotic lesions developed in mice fed a low-iron diet were significantly smaller than those found in control littermates. Likewise, the iron deposition as well as tissue iron content was much less in aortic tissues of the iron-restricted animals. Circulating autoantibodies to oxidized LDL and immunostains for epitopes of malondialdehyde-modified LDL detected on lesions were also significantly lower in mice fed a low-iron diet. CONCLUSIONS: Iron deposition is closely associated with the progression of atherosclerosis in apoE-deficient mice. Restriction in dietary iron intake leads to significant inhibition of lesion formation in these animals. These results suggest that the beneficial effect of a low-iron diet may be mediated, at least in part, by the reduction of iron deposition as well as LDL oxidation in vascular lesions. (+info)
Effect of iron-, iodine-, and beta-carotene-fortified biscuits on the micronutrient status of primary school children: a randomized controlled trial.
BACKGROUND: Deficiencies of iron, iodine, and vitamin A are prevalent worldwide and can affect the mental development and learning ability of schoolchildren. OBJECTIVE: The aim of this study was to determine the effect of micronutrient-fortified biscuits on the micronutrient status of primary school children. DESIGN: Micronutrient status was assessed in 115 children aged 6-11 y before and after consumption of biscuits (fortified with iron, iodine, and beta-carotene) for 43 wk over a 12-mo period and was compared with that in a control group (n = 113) who consumed nonfortified biscuits. Cognitive function, growth, and morbidity were assessed as secondary outcomes. RESULTS: There was a significant between-group treatment effect on serum retinol, serum ferritin, serum iron, transferrin saturation, and urinary iodine (P <0.0001) and in hemoglobin and hematocrit (P <0.05). The prevalence of low serum retinol concentrations (<0.70 micromol/L) decreased from 39.1% to 12.2%, of low serum ferritin concentrations (<20 microg/L) from 27.8% to 13.9%, of anemia (hemoglobin <120 g/L) from 29.6% to 15.6%, and of low urinary iodine concentrations (<100 microg/L) from 97.5% to 5.4%. There was a significant between-group treatment effect (P <0.05) in cognitive function with the digit span forward task (short-term memory). Fewer school days were missed in the intervention than in the control group because of respiratory- (P = 0.097) and diarrhea-related (P = 0.013) illnesses. The intervention had no effect on anthropometric status [corrected]. CONCLUSIONS: Fortified biscuits resulted in a significant improvement in the micronutrient status of primary school children from a poor rural community and also appeared to have a favorable effect on morbidity and cognitive function [corrected]. (+info)