Stored iron and ischemic heart disease. Empirical support for a new paradigm

Non-Transferrin-Bound Iron in the Spotlight: Novel Mechanistic Insights into the Vasculotoxic and Atherosclerotic Effect of Iron

Significance: While atherosclerosis is an almost inevitable consequence of aging, food preferences, lack of exercise, and other aspects of the lifestyle in many countries, the identification of new risk factors is of increasing importance to tackle a disease, which has become a major health burden for billions of people. Iron has long been suspected to promote the development of atherosclerosis, but data have been conflicting, and the contribution of iron is still debated controversially. Recent Advances: Several experimental and clinical studies have been recently published about this longstanding controversial problem, highlighting the critical need to unravel the complexity behind this topic. Critical Issues: The aim of the current review is to provide an overview of the current knowledge about the proatherosclerotic impact of iron, and discuss the emerging role of non-transferrin-bound iron (NTBI) as driver of vasculotoxicity and atherosclerosis. Finally, I will provide detailed mechanistic insights on the cellular processes and molecular pathways underlying iron-exacerbated atherosclerosis. Overall, this review highlights a complex framework where NTBI acts at multiple levels in atherosclerosis by altering the serum and vascular microenvironment in a proatherogenic and proinflammatory manner, affecting the functionality and survival of vascular cells, promoting foam cell formation and inducing angiogenesis, calcification, and plaque destabilization. Future Directions: The use of additional iron markers (e.g., NTBI) may help adequately predict predisposition to cardiovascular disease. Clinical studies are needed in the aging population to address the atherogenic role of iron fluctuations within physiological limits and the therapeutic value of iron restriction approaches. Antioxid. Redox Signal. 35, 387-414.

Low serum iron levels and risk of cardiovascular disease in high risk elderly population: Nested case-control study in the PREvención con DIeta MEDiterránea (PREDIMED) trial

BACKGROUND & AIMS

Epidemiological data on iron status and cardiovascular disease (CVD) are still controversial. The aim of this study was to determine whether low serum iron (SI) levels are associated with an increased odds of first CVD event in a population at high cardiovascular risk.

METHODS

Case-control study design nested within the "PREvención con DIeta MEDiterránea" (PREDIMED) trial. A total of 207 participants diagnosed with CVD (myocardial infarction, stroke or cardiovascular death) during follow-up period (2003-2010) were matched by sex, age and intervention group to 436 controls by incidence density sampling. Median time between serum sample collection and subsequent CVD event occurrence was 0.94 years. Inductively coupled plasma mass spectrometry analysis was used to determine SI levels. In-person interviews, medical record reviews, and validated questionnaires were used to assess covariates. Multivariable-adjusted odds ratios (ORs) of CVD were calculated with conditional logistic regression.

RESULTS

Mean SI levels were higher in men than in women (1224.0 μg/L vs. 1093.8 μg/L; p < 0.001). Among women, but not in men, the mean SI concentration was lower in cases than in controls (1008.5 μg/L vs. 1132.9 μg/L; p = 0.030). There was a gradual decrease in the multivariable-adjusted ORs of CVD with increasing SI levels (highest vs. lowest quartile: OR = 0.55, 95% CI: 0.32-0.93; p_trend = 0.020). This inverse relationship was more pronounced among women (highest vs. lowest quartile: OR = 0.15, 95% CI: 0.03-0.69; p_trend = 0.011).

CONCLUSIONS

The present findings are consistent with previously reported inverse associations between SI and CVD. SI levels as an independent marker of short-term cardiovascular risk may be useful for risk assessment in older populations.

TRIAL REGISTRATION

www.controlled-trials.com; International Standard Randomized Controlled Trial Number (ISRCTN): 35,739,639. Registered 5 October 2005. Retrospectively registered.

Gamma-Glutamyltransferase: A Predictive Biomarker of Cellular Antioxidant Inadequacy and Disease Risk

Gamma-glutamyltransferase (GGT) is a well-established serum marker for alcohol-related liver disease. However, GGT's predictive utility applies well beyond liver disease: elevated GGT is linked to increased risk to a multitude of diseases and conditions, including cardiovascular disease, diabetes, metabolic syndrome (MetS), and all-cause mortality. The literature from multiple population groups worldwide consistently shows strong predictive power for GGT, even across different gender and ethnic categories. Here, we examine the relationship of GGT to other serum markers such as serum ferritin (SF) levels, and we suggest a link to exposure to environmental and endogenous toxins, resulting in oxidative and nitrosative stress. We observe a general upward trend in population levels of GGT over time, particularly in the US and Korea. Since the late 1970s, both GGT and incident MetS and its related disorders have risen in virtual lockstep. GGT is an early predictive marker for atherosclerosis, heart failure, arterial stiffness and plaque, gestational diabetes, and various liver diseases, including viral hepatitis, other infectious diseases, and several life-threatening cancers. We review literature both from the medical sciences and from life insurance industries demonstrating that serum GGT is a superior marker for future disease risk, when compared against multiple other known mortality risk factors.

Association between sex, systemic iron variation and probability of Parkinson's disease

OBJECTIVE

Iron homeostasis appears altered in Parkinson's disease (PD). Recent genetic studies and meta-analyses have produced heterogeneous and inconclusive results. In order to verify the possible role of iron status in PD, we have screened some of the main metal gene variants, evaluated their effects on iron systemic status, and checked for possible interactions with PD.

MATERIALS AND METHODS

In 92 PD patients and 112 healthy controls, we screened the D544E and R793H variants of the ceruloplasmin gene (CP), the P589S variant of the transferrin gene (TF), and the H63D and C282Y variants of the HFE gene, encoding for homologous proteins, respectively. Furthermore, we analyzed serum concentrations of iron, copper and their related proteins.

RESULTS

The genetic investigation revealed no significant differences in allelic and genotype distributions between patients and controls. Two different multivariable forward stepwise logistic models showed that, when the effect of sex is considered, an increase of the probability of having PD is associated with low iron concentration and Tf-saturation.

CONCLUSIONS

This study provides new evidence of the involvement of iron metabolism in PD pathogenesis and reveals a biological effect of sex.

Association of low serum iron levels with low-grade inflammation and hyperadiponectinemia in community-living elderly women

AIM

There have been inconsistent reports regarding the relationship between the iron status and coronary vascular diseases (CVD). Recently, low serum iron levels have been shown to be associated with mortality from CVD in women.

METHODS

The relationships between the serum iron levels and traditional and nontraditional risk factors for CVD were examined in 202 community-living elderly Japanese women.

RESULTS

The women in the lowest iron tertile had higher high-sensitivity C-reactive protein (hsCRP) and tumor necrosis factor-α (TNF-α) levels than the women in the top iron tertile (p<0.01 or less for both). In addition, the women in the lowest tertile had higher serum levels of adiponectin and copper and ratios of serum copper to zinc and lower serum levels of albumin, hemoglobin and hematocrit. Furthermore, the women in the lowest tertile had higher creatinine levels and lower eGFR values, although there were no significant differences in the prevalence of chronic kidney disease between the three tertile groups. In a multiple regression analysis including the levels of hsCRP, TNF-α, adiponectin and serum creatinine and the ratio of serum copper to zinc as independent variables, the levels of hsCRP, TNF-α and adiponectin emerged as independent determinants of the serum iron level (R(2)= 0.106). In the model to which the hemoglobin level was added as an independent variable, the levels of hemoglobin, hsCRP and TNF-α emerged as independent determinants of the serum iron level (R(2)= 0.192).

CONCLUSIONS

The present study demonstrated that community-living elderly Japanese women with low serum iron levels have nontraditional risk factors for CVD, including low-grade inflammation and higher levels of serum adiponectin.

On myocardial siderosis and left ventricular dysfunction in hemochromatosis

BACKGROUND

Chronically increased intestinal iron uptake in genetic hemochromatosis (HC) may cause organ failure. Whilst iron loading from blood transfusions may cause dilated cardiomyopathy in conditions such as thalassemia, the in-vivo prevalence of myocardial siderosis in HC is unclear, and its relation to left ventricular (LV) dysfunction is controversial. Most previous data on myocardial siderosis in HC has come from post-mortem studies.

METHODS

Cardiovascular magnetic resonance (CMR) was performed at first presentation of 41 HC patients (58.9 ± 14.1 years) to measure myocardial iron and left ventricular (LV) ejection fraction (EF).

RESULTS

In 31 patients (genetically confirmed HFE-HC), the HFE genotype was C282Y/C282Y (n = 30) and C282Y/H63D (n = 1). Patients with other genotypes (n = 10) were labeled genetically unconfirmed HC. Of the genetically confirmed HFE-HC patients, 6 (19%) had myocardial siderosis (T2* <20 ms). Of these, 5 (83%) had heart failure and reduced LVEF which was correlated to the severity of siderosis (R2 0.57, p = 0.049). Two patients had follow-up scans and both had marked improvements in T2* and LVEF following venesection. Myocardial siderosis was present in 6/18 (33%) of patients with presenting ferritin ≥ 1000 μg/L at diagnosis but in 0/13 (0%) patients with ferritin <1000 μg/L (p = 0.028). Overall however, the relation between myocardial siderosis and ferritin was weak (R2 0.20, p = 0.011). In the 10 genetically unconfirmed HC patients, 1 patient had mild myocardial siderosis but normal EF. Of all 31 patients, 4 had low LVEF from other identifiable causes without myocardial siderosis.

CONCLUSION

Myocardial siderosis was present in 33% of newly presenting genetically confirmed HFE-HC patients with ferritin >1000 μg/L, and was the commonest cause of reduced LVEF. Heart failure due to myocardial siderosis was only found in these HFE-HC patients, and was reversible with venesection. Myocardial iron was normal in patients with other causes of LV dysfunction.

Nutritional biochemistry of spaceflight

As we approach the end of the first 50 years of human space travel, much has been learned about adaptation to microgravity and the risks associated with extended-duration space exploration. As the frequency and duration of flights grew, nutrition issues became more critical and the questions to be answered became more complex: What are the nutrient requirements for space travelers? Can nutrients be used as tools to mitigate the negative effects of space travel on humans? How does nutrition interrelate with other physiological systems (such as muscle, bone, and cardiovascular system) and their adaptation to microgravity? Much research has been done over the decades in both actual spaceflight and ground-based analogs. We review here much of what is known, and highlight areas of ongoing research and concerns for future exploration of the Moon, Mars, and beyond.

Macrophage iron, hepcidin, and atherosclerotic plaque stability

Hepcidin has emerged as the key hormone in the regulation of iron balance and recycling. Elevated levels increase iron in macrophages and inhibit gastrointestinal iron uptake. The physiology of hepcidin suggests an additional mechanism by which iron depletion could protect against atherosclerotic lesion progression. Without hepcidin, macrophages retain less iron. Very low hepcidin levels occur in iron deficiency anemia and also in homozygous hemochromatosis. There is defective retention of iron in macrophages in hemochromatosis and also evidently no increase in atherosclerosis in this disorder. In normal subjects with intact hepcidin responses, atherosclerotic plaque has been reported to have roughly an order of magnitude higher iron concentration than that in healthy arterial wall. Hepcidin may promote plaque destabilization by preventing iron mobilization from macrophages within atherosclerotic lesions; the absence of this mobilization may result in increased cellular iron loads, lipid peroxidation, and progression to foam cells. Marked downregulation of hepcidin (e.g., by induction of iron deficiency anemia) could accelerate iron loss from intralesional macrophages. It is proposed that the minimally proatherogenic level of hepcidin is near the low levels associated with iron deficiency anemia or homozygous hemochromatosis. Induced iron deficiency anemia intensely mobilizes macrophage iron throughout the body to support erythropoiesis. Macrophage iron in the interior of atherosclerotic plaques is not exempt from this process. Decreases in both intralesional iron and lesion size by systemic iron reduction have been shown in animal studies. It remains to be confirmed in humans that a period of systemic iron depletion can decrease lesion size and increase lesion stability as demonstrated in animal studies. The proposed effects of hepcidin and iron in plaque progression offer an explanation of the paradox of no increase in atherosclerosis in patients with hemochromatosis despite a key role of iron in atherogenesis in normal subjects.

Serum ferritin in stroke: a marker of increased body iron stores or stroke severity?

To evaluate the effect of body iron stores on the vulnerability of the brain to ischemia, a focal permanent brain ischemia was induced by photothrombotic occlusion of cortical vessels in rats with or without chronic treatment with iron dextran (25 mg iron/kg, every other day for 20 days, intraperitoneally). Iron dextran induced systemic iron overload as evidenced by high ferritin (Ft) ( x 5) and total iron levels ( x 3) in serum as well as increased Ft expression in the liver and heart. Conversely, neither serum free iron levels nor Ft expression in the brain were changed by iron dextran. Finally, infarct volume was not modified by iron dextran. In addition, induction of ischemia in rats treated with FeCl(3) (560 microg iron/kg, intravenously) as a means of increasing serum free iron levels during the ischemic period did not enlarge infarct volume. We then explored the effect of brain ischemia itself on serum Ft by measuring serum Ft before and after induction of brain ischemic insults with different neurologic outcomes in rats (brain embolization with microspheres, photothrombotic occlusion of cortical vessels, four-vessel occlusion). Serum Ft levels were found higher at day 1 after ischemia than before ischemia only in rats subjected to the most severe insult (brain embolization). In conclusion, our study showed that increased body iron stores do not increase the vulnerability of the brain to ischemia and that brain ischemia, if severe, results in the elevation of serum Ft levels.

Iron accumulation during cellular senescence in human fibroblasts in vitro

Iron accumulates as a function of age in several tissues in vivo and is associated with the pathology of numerous age-related diseases. The molecular basis of this change may be due to a loss of iron homeostasis at the cellular level. Therefore, changes in iron content in primary human fibroblast cells (IMR-90) were studied in vitro as a model of cellular senescence. Total iron content increased exponentially during cellular senescence, resulting in 10-fold higher levels of iron compared with young cells. Low-dose hydrogen peroxide (H2O2) induced early senescence in IMR-90s and concomitantly accelerated iron accumulation. Furthermore, senescence-related and H2O2-stimulated iron accumulation was attenuated by N-tert-butylhydroxylamine (NtBHA), a mitochondrial antioxidant that delays senescence in vitro. However, SV40-transformed, immortalized IMR-90s showed no time-dependent changes in metal content in culture or when treated with H2O2 and/or NtBHA. These data indicate that iron accumulation occurs during normal cellular senescence in vitro. This accumulation of iron may contribute to the increased oxidative stress and cellular dysfunction seen in senescent cells.

Influence of target hemoglobin in dialysis patients on morbidity and mortality

Since the introduction of recombinant human erythropoietin (rHuEPO) in 1989, the level of anemia correction has been debated. Information developed from clinical trials and observational studies have given conflicting results. The normal hematocrit (Hct) trial of Besarab et al showed no benefit, and a possible risk, of correcting the Hct from 30% to 42% in hemodialysis patients with NYHA class I to III cardiac disease. The study of Moreno et al in non-cardiac patients showed improved Sickness Impact Profile and Karnofsky scores in hemodialysis patients when their Hct was increased from 31% to 38.5%. Hospitalizations were significantly reduced. Observational studies from Madore et al, Xia et al, Ma et al, and Collins et al all show that increased morbidity and mortality are significantly associated with Hct <33%. Recent data on incident hemodialysis patients indicate the associated risk of death was not different for patients with Hct 33 to <36% versus Hct 36 to <39%. Hospitalization risks and associated costs were significantly less in the patients with Hct 36 to <39%, suggesting that higher Hct values may be less of a concern than previously considered. The current data suggest that patents with advanced cardiac disease should avoid Hct values in the normal range. In others, Hcts at least up to 39% appear to be safe and effective. Based on this review, a reasonable target Hct range may be 33 to 39%, which balances the risks and potential benefits.

Impact of body iron status on myocardial perfusion, left ventricular function, and angiographic morphologic features in patients with hypercholesterolemia

BACKGROUND

Previous studies have shown that the effects of iron stores on atherogenesis through promotion of free radical formation and low-density lipoprotein (LDL) oxidation largely depend on the state of hypercholesterolemia (HCL) in animal models. A synergistic association of serum ferritin and LDL cholesterol with the risk of myocardial infarction has also been observed in humans.

METHODS

We sought to assess the relationship of serum iron parameters to myocardial perfusion and wall motion abnormalities and to the extent of angiographic coronary artery disease (CAD) in patients with HCL. Sixty-eight male patients (mean age 58 +/- 9 years) with hypercholesterolemia (LDL cholesterol >130 mg/dL) who had never been treated and 52 normocholesterolemic male subjects of similar age underwent coronary angiography and exercise technetium-99m sestamibi gated single-photon emission computed tomography imaging within 10 days.

RESULTS

Serum ferritin had a significant correlation with the perfusion index (r = 0.70, P <.001), the reversibility index (r = 0.68, P <.01), and the wall motion index (r = 0.54, P <.05), whereas a relatively weak correlation was observed between total iron binding capacity and perfusion index (inversely) (r = -0.59, P <.01) in patients with HCL. Iron parameters were not associated with either perfusion or wall motion indices in the normocholesterolemic group. Stepwise multiple regression analysis confirmed these results. Ferritin was a strong determinant of perfusion in patients with HCL only (beta =.55, P =.002). Iron parameters were not related to the angiographic extent of CAD as defined by angiographic vessel or extent score in either group.

CONCLUSIONS

Our data suggest that increased iron stores are closely associated with a greater extent and severity of perfusion and functional abnormalities but not with the angiographic extent of CAD in patients with HCL. Enhanced iron-mediated oxidative stress and LDL peroxidation may contribute to the hypercholesterolemia-related endothelial dysfunction and cause further impairment of myocardial perfusion and wall motion.

Hemochromatosis gene variants in patients with cardiomyopathy

Iron depletion was suggested to be protective against the development of ischemic heart disease. Population studies have led to conflicting results, and such an association has not been addressed in patients with heart failure due to cardiomyopathy. We studied the distribution of hemochromatosis-related mutations in 319 patients with heart failure due to cardiomyopathy of different etiologies. The genotypic distribution showed a significantly higher prevalence of heterozygotes for the C282Y mutation in patients with ischemic cardiomyopathy than in patients with cardiomyopathy of nonischemic etiologies (p = 0.0036). The frequency of the D63 mutation was not significantly different between ischemic versus nonischemic groups. In multiple logistic regression models adjusted for age, sex, ethnicity, and different degrees of disease progression, there was a strong and significant association of the C282Y mutation with ischemic cardiomyopathy compared with the nonischemic group (odds ratio 6.64, 95% confidence interval 1.71 to 25.73, after adjustment). In our sample, genetic variation in the HFE gene was associated with ischemic cardiomyopathy. Such association merits further study regarding its value as a prognostic marker in patients with ischemic heart disease.

Iron overload can induce mild copper deficiency

Dietary copper in the U.S. often is lower than that proved insufficient for men and women under controlled conditions. Iron overload can have adverse effects on copper nutriture and can produce cardiac disease in people. The hypothesis that iron can interfere with copper utilization to produce adverse effects related to cardiovascular function was tested. Rats were fed a diet high in iron and marginal, but not deficient in copper for comparison with similar diets containing iron at the recommended amount. Copper and iron were measured by atomic absorption spectroscopy; cholesterol was measured by fluorescence, ceruloplasmin was measured by oxidase activity and hematology was done by an automated cell counter. When dietary copper was 2.0 mg/kg of diet, high iron decreased (p<0.008) cardiac and hepatic copper, plasma copper and ceruloplasmin, and increased (p<0.02) cardiac weight, hepatic iron and plasma cholesterol. When dietary copper was increased to 2.5 mg/kg, copper in heart and plasma decreased (p<0.04) and hepatic iron increased (p=0.001) with high iron but other effects disappeared. No harmful changes in hematology, such as hematocrit, mean corpuscular volume, etc. were found. High iron increased the dietary copper requirement of the animals. People with iron overload may benefit from copper supplementation, particularly if they habitually consume a diet low in copper.

Association of age, sex, and race with body iron stores in adults: analysis of NHANES III data

BACKGROUND

This study examined age-, sex-, and race- related increases in body iron stores that have been implicated in disease and the relative utility of the serum ferritin versus the percentage of transferrin saturation for population-based estimation of iron status.

METHODS AND RESULTS

Serum ferritin levels were examined by age, sex, and race, and values were compared with the percent transferrin saturation in 20,040 individuals >17 years of age from the third National Health and Nutrition Examination Survey (NHANES III) database. Body iron stores reflected by serum ferritin levels rose in the late teens in men and after menopause in women. This rise was more rapid and maximum ferritin levels were greater for blacks than whites and Hispanics of comparable age and sex. The distribution of values for the serum ferritin differed from the percent transferrin saturation.

CONCLUSIONS

Different patterns of iron accumulation exist according to age, sex, and race. Serum ferritin levels reflect graded, population-based differences in body iron stores, but the percentage of transferrin saturation does not. The hypothesis that iron accumulation may contribute to higher morbidity and mortality rates can be tested in clinical trials of calibrated reduction of body iron stores in defined disease settings.

Insulin resistance-associated hepatic iron overload

BACKGROUND & AIMS

Hepatic iron overload has been reported in various metabolic conditions, including the insulin-resistance syndrome (IRS) and nonalcoholic steatohepatitis (NASH). The aim of this study was to show that such hepatic iron overload is part of a unique and unrecognized entity.

METHODS

A total of 161 non-C282Y-homozygous patients with unexplained hepatic iron overload were included. We determined the age; sex; presence of IRS (1 or more of the following: body mass index of >25, diabetes, or hyperlipidemia); serum iron tests and liver iron concentration (LIC; reference value, <36 micromol/g); liver function test results; C282Y and H63D HFE mutations; and liver histological status.

RESULTS

Patients were predominantly male and middle-aged. Most (94%) had IRS. Transferrin saturation was increased in 35% (median, 42%; range, 13%-94%). LIC ranged from 38 to 332 micromol/g (median, 90 micromol/g), and LIC/age ratio ranged from 0.5 to 4.8 (median, 1.8). Allelic frequencies of both HFE mutations were significantly increased compared with values in normal controls (C282Y, 20% vs. 9%; H63D, 30% vs. 17%), only because of a higher prevalence of compound heterozygotes. Patients with no HFE mutations had similar degrees of iron overload as those with other genotypes, except for compound heterozygotes, who had slightly more iron burden. Steatosis was present in 25% of patients and NASH in 27%. Portal fibrosis (grades 0-3) was present in 62% of patients (grade 2 or 3 in 12%) in association with steatosis, inflammation, and increased age. Sex ratio, IRS, transferrin saturation, and LIC did not vary with liver damage. Serum ferritin concentration, liver function test results, and fibrosis grade were more elevated in patients with steatosis and NASH than in others, but LIC and allelic frequencies of HFE mutations were similar.

CONCLUSIONS

This study shows that patients with unexplained hepatic iron overload are characterized by a mild to moderate iron burden and the nearly constant association of an IRS irrespective of liver damage.

The antioxidant defense protein ferritin is a novel and specific target for pentaerithrityl tetranitrate in endothelial cells

The organic nitrate pentaerithrityl tetranitrate (PETN) is known to exert long-term antioxidant and antiatherogenic effects by as yet unidentified mechanisms. In porcine aortic endothelial cells, a 24 h incubation with PETN (1-100 microM) or its metabolite pentaerithrityl trinitrate (PETriN) increased levels of the antioxidant protein ferritin up to three-fold over basal, whereas isosorbide dinitrate and isosorbide-5-mononitrate were without significant effect under these conditions. PETriN-induced ferritin expression was blocked by the NO scavenger PTIO but remained unaltered in the presence of ODQ, an inhibitor of soluble guanylyl cyclase. 8-Bromo cyclic GMP and dibutyryl cyclic GMP did not influence basal ferritin synthesis. The iron chelator desferrioxamine abolished ferritin induction by PETriN. Our results show that PETN or its active metabolite PETriN induce ferritin synthesis through NO- and iron-dependent but cyclic GMP-independent pathways. Increased activity of ferritin may contribute to, and at least in part explain, the specific antiatherogenic and antioxidant action of PETN.

Dietary copper primarily affects antioxidant capacity and dietary iron mainly affects iron status in a surface response study of female rats fed varying concentrations of iron, zinc and copper

This study was designed to examine the interactions among dietary iron (Fe), copper (Cu), and zinc (Zn) and their effects on Fe status and oxidative stress in female rats. In a three-factor central composite response surface design, rats were assigned to 15 groups and fed modified AIN-93G basal diets with varying amounts of Fe and Zn (7.0, 15.5, 45.8, 135.6, or 300 micrograms/g diet) and Cu (0.5, 1.1, 3.2, 9.2, or 20 micrograms/g diet) for 6 wk. Variations in hemoglobin, hematocrit, and serum ferritin were mainly related to dietary Fe. Liver nonheme Fe was directly affected by dietary Fe and was slightly attenuated by interactions between Cu and Zn, and Zn and Fe. Serum ceruloplasmin activity was primarily determined by an interaction between Cu and Zn with substantial moderation by the quadratic effect of dietary Cu. Liver and heart total superoxide dismutase (SOD) and Cu/Zn SOD activities were directly affected by dietary Cu. Dietary Fe was the only significant, yet weak, predictor of liver thiobarbituric acid reactive substances (TBARS) and vitamin E content and serum triacylglycerols. Variability in serum Cu was mostly determined by the interaction between Cu and Fe, with modification from the quadratic effect of dietary Cu. Serum Zn varied with dietary Zn with a small negative influence from the interaction between Cu and Fe. In summary, Fe status was minimally influenced by dietary Zn or Cu, and Fe intakes 10-fold greater than required did not induce overt oxidative stress in female rats. In addition, measures of antioxidant capacity were primarily influenced by dietary Cu and were optimal at moderate intakes of this micronutrient.

Iron therapy and cardiovascular disease

Intensive iron therapy is now a generally accepted adjunct for the treatment of renal anemia with recombinant human erythropoietin. However, with the emerging role of iron in cardiovascular disease, carcinogenesis, infectious diseases, and other disorders, it is no longer appropriate to assume that any amount of stored iron is safe until proven otherwise. In this article, the history and current status of the "iron hypothesis" on ischemic heart disease are briefly reviewed, followed by comments on iron management practices for renal patients.

Serum iron level, coronary artery disease, and all-cause mortality in older men and women

The association between iron levels and coronary artery disease (CAD) mortality is controversial. Whereas most data show no association, some have raised the possibility of a causal role, while others have suggested a protective effect of iron on CAD. To address these possibilities, we examined the association between serum iron and CAD, cardiovascular disease, and all-cause mortality in a large cohort of 3,936 persons aged > or =71 years who completed an interview, had a serum iron determination, and survived at least 1 year after baseline. The median follow-up time was 4.4 years. Serum iron levels were categorized according to sex-specific quartiles. Relative risks (RR) and 95% confidence intervals (CI) were calculated from proportional-hazards regression models adjusted for age, race, education, creatinine, serum albumin, serum lipids, use of iron supplementation, smoking, use of alcohol, blood pressure, body mass index, and presence of chronic conditions. There was a gradual decrease in the RRs of CAD, cardiovascular disease, and all-cause mortality with increasing serum iron levels (all tests for trend, p <0.05). Men in the highest iron quartile were one fifth as likely to die of CAD as men in the lowest iron quartile (RR 0.22; 95% CI 0.11 to 0.48), and women in the highest quartile had half the risk of women in the lowest quartile (RR 0.48; 95% CI 0.27 to 0.87). When compared with the lowest quartile, risk of all-cause mortality was 38% lower in men in the highest iron quartile (RR 0.62; 95% CI 0.46 to 0.85) and 28% lower in women in the highest quartile (RR 0.72; 95% CI 0.53 to 0.96). Results of similar strength and magnitude were observed for cardiovascular disease mortality and in analyses that excluded the first 3 years of follow-up. In this large cohort of persons aged > or =71 years, there was consistent evidence of increasing risk of mortality at lower serum iron levels. In fact, lower serum iron levels were associated with an increased risk of CAD, cardiovascular disease, and all-cause mortality. The results are compatible with the possibility that in an older population, there is an inverse association between serum iron levels and risk of mortality.

Iron status and risk of cardiovascular disease

Free Iron, as well as other transition metals, can catalyze free radical formation. For this reason iron is tightly bound to transport and storage proteins to prevent their involvement in free radical formation. It has been hypothesized that increased iron intake or iron stores may promote atherogenesis by increasing free radical formation and oxidative stress. While a coherent, plausible hypothesis as to how transition metals, such as iron, might accelerate the progression of atherosclerosis has been generated from basic research, iron status, measured as dietary iron intake, serum iron, serum ferritin, and transferrin saturation, has been inconsistently associated with cardiovascular disease in human epidemiologic research. In addition, limited data suggest that iron overload states do not appear to be strongly associated with increased risk of atherosclerotic disease. One real limitation of the existing data is the lack of a generally agreed upon and logistically feasible means of assessing iron status in free living humans. Further research, including basic research and large-scale epidemiologic studies, is needed to fully assess the association between iron status and the risk of CVD and other adverse outcomes. At present the currently available data do not support radical changes in dietary recommendations or screening to detect high normal levels nor do they support the need for large-scale randomized trials of dietary restriction or phlebotomy as a means of lowering iron stores.

Iron versus cholesterol--perspectives on the iron and heart disease debate

Focusing only on the limited question of whether stored iron is a valid heart disease risk factor inappropriately narrows the scope of the debate on the "iron hypothesis." Framing the debate in this way ignores the broad explanatory power of the hypothesis that iron depletion protects against ischemic heart disease. The iron hypothesis provides a conceptual tool for study of the mechanisms by which age and gender influence the development of ischemic heart disease. The assumption that age and gender exert unalterable effects has diverted attention from these strong risk factors, and has led to intense preoccupation with weaker risk factors such as cholesterol. The notion that cholesterol is of central importance has become a rigid and institutionalized point of view. Increased mortality from some cholesterol-lowering drugs is but one of the potential dangers of continued promotion of the flawed idea that heart disease is a function of the cholesterol concentration. The more serious risk is that alternative approaches to the problem of ischemic heart disease will be suppressed. Consideration of the relationship between the iron and cholesterol hypotheses provides important perspectives on the current debate on the role of iron in the development of ischemic heart disease.

Iron metabolism: a comprehensive review

Despite its abundance in the earth's crust, iron deficiency is a serious health issue in many parts of the world. Although fundamental observations about iron metabolism and the significance of iron nutriture were first noted some time ago, the molecular mechanisms involved in iron metabolism are just now being defined.

Iron and heart disease: the epidemiologic data

There has developed a general theory of chronic and degenerative disease causation--the Oxidative Stress Theory. This theory states that the production of tissue-damaging free radicals is an essential component in the pathogenesis of chronic diseases and that iron may help to catalyze the reactions producing free radicals. As a result, it has been suggested that the risk of coronary heart disease increases with increasing body iron stores. In support of that hypothesis, a prospective epidemiologic study of heart disease in Finnish men found that the risk of heart attack increased with increasing levels of serum ferritin. However, the vast majority of the epidemiologic data, including results from prospective, cross-sectional, and case-control and autopsy studies, published since that initial study have failed to support the original hypothesis that high body iron stores increase the risk of coronary heart disease.

Up-regulation of intracellular signalling pathways may play a central pathogenic role in hypertension, atherogenesis, insulin resistance, and cancer promotion--the 'PKC syndrome'

The modern diet is greatly different from that of our paleolithic forebears' in a number of respects. There is reason to believe that many of these dietary shifts can up-regulate intracellular signalling pathways mediated by free intracellular calcium and protein kinase C, particularly in vascular smooth muscle cells; this disorder of intracellular regulation is given the name 'PKC syndrome'. PKC syndrome may entail either a constitutive activation of these pathways, or a sensitization to activation by various agonists. The modern dietary perturbations which tend to induce PKC syndrome may include increased dietary fat and sodium, and decreased intakes of omega-3 fats, potassium, calcium, magnesium and chromium. Insulin resistance may be both a cause and effect of PKC syndrome, and weight reduction and aerobic training should act to combat this disorder. PKC syndrome sensitizes vascular smooth muscle cells to both vasoconstrictors and growth factors, and thus promotes both hypertension and atherogenesis. In platelets, it induces hyperaggregability, while in the microvasculature it may be a mediator of diabetic microangiopathy. In vascular endothelium, intimal macrophages, and hepatocytes, increased protein kinase C activity can be expected to increase cardiovascular risk. Up-regulation of protein kinase C in stem cells may also play a role in the promotion of 'Western' fat-related cancers. Practical guidelines for combatting PKC syndrome are suggested.

New concepts regarding events that lead to myocardial infarction

In addition to new knowledge concerning the mechanisms whereby conventional risk factors act, other risk factors have been newly described, such as dietary antioxidants, lack of exercise, insulin resistance, excess iron stores, increased plasma angiotensin-converting enzyme, and left ventricular hypertrophy. An intact endothelium protects both by the formation of nitric oxide, which is a vasodilator and also an inhibitor of platelet aggregation and neutrophil adhesion, and by manufacturing tissue plasminogen activator. The acute thrombotic event occurs with a diurnal variation but may be precipitated by acute exertion, especially in untrained individuals, and reflects a balance between vasoconstrictory and vasodilatory stimuli from the vascular endothelium, as well as procoagulant versus anticoagulant effects of complex balancing systems. Increased risk of sudden cardiac death in the morning is thought to be a reflection of transient risk factors, such as a blood pressure increase, heart rate increase, and changes in coagulation factors, as well as changes in platelet aggregation. There is an apparent paradox between the acute effect of exercise in promoting sudden cardiac death and the chronic effect of exercise training in decreasing the risk of myocardial infarction. The explanation may be that chronic exercise training has an inhibitory effect on adrenergic discharge.

Gender does not influence acute myocardial infarction in adult dogs

Mechanisms responsible for the well-documented "protection" against myocardial ischemia and infarction in young women and subsequent loss of protection after menopause remain speculative. One possibility is that gender-related variables (such as endogenous hormone levels or regular loss of stored iron) alter the susceptibility of the heart to ischemia: if so, then premenopausal women when compared with men may manifest endogenous protection against acute myocardial ischemic injury. Using the canine model we therefore sought to determine whether gender influences acute myocardial ischemia and infarction. Retrospective analysis was performed on data compiled from 60 mature adult dogs subjected to 1 hour of coronary artery occlusion and > or = 4 hours of reperfusion. We first compared the incidence of lethal ventricular fibrillation in the male and female cohorts and then for survivors compared collateral blood flow during coronary occlusion (by injection of radioactive microspheres), infarct size (assessed by tetrazolium staining and expressed as a percentage of the myocardium at risk), and regional wall motion (by somomicrometry) in the infarct-related area. The incidence of lethal ventricular fibrillation was 23% in the male dogs and 19% in the female dogs (p = 0.70, difference not significant). For survivors, the area at risk of infarction was comparable in males and females (23 +/- 2% and 22% +/- 1% of the total left ventricular weight), and the groups were equally ischemic during coronary occlusion, with collateral blood flow to the ischemic subendocardium averaging 0.05 +/- 0.02 and 0.07 +/- 0.01 ml/min/g tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

The health effects of vitamin C supplementation: a review

A comprehensive review of the literature indicates that populations with long-term consumption of higher than RDA levels of vitamin C (> or = 60 mg/day) from foods and/or supplements have reduced risks of cancer at several sites, cardiovascular disease, and cataracts. The safety of higher than RDA intakes of vitamin C is confirmed in eight placebo-controlled, double-blind studies and six non-placebo clinical trials in which up to 10,000 mg of vitamin C was consumed daily for up to 3 years. There are no clinical data which suggest that vitamin C's enhancement of non-heme iron absorption in individuals with low iron status could be a critical factor in the possible increased risk of heterozygous hemochromatosis-related cardiovascular disease. In fact, the cumulative data do not confirm that iron status is related to risk of cardiovascular disease. Moreover, higher than RDA intakes of vitamin C have been associated with several indices of lowered cardiovascular disease risk including increases in HDL, and decreases in LDL oxidation, blood pressure and cardiovascular mortality.

Synthesis and iron(III) binding properties of 3-hydroxypyrid-4-ones derived from kojic acid

In an attempt to reduce the toxicity of the 3-hydroxypyrid-4-ones, the more hydrophilic derivatives of kojic acid were explored and compared to the standard, 1,2-dimethyl-3-hydroxypyrid-4-one, L1. The synthesis and iron(III) binding properties of these chelators are described. Neither these compounds nor the clinically effective 1,2-dimethyl-3-hydroxypyrid-4 one is able to completely remove all of the iron(III) from the Fe(III)EDTA complex in sodium acetate buffered solutions, when the 3-hydroxypyrid-4-one: Fe(III) ratio is 6:1. The ability of these compounds to enhance the urinary excretion of iron in rats indicates that the behavior of the 3-hydroxypyrid-4-ones derived from kojic acid is comparable to the analogous derivatives of maltol and ethyl maltol. The structure of the iron(III) complex of 3-hydroxy-6-hydroxymethyl-1-methylpyrid-4-one was determined by x-ray diffraction and found to be similar to the previously reported structure of the iron(III) complex of L1.

Iron-related damage in acute ischemic stroke

BACKGROUND AND PURPOSE

Although iron-mediated mechanisms are important in experimental brain injury after carotid occlusion, their clinical role in acute ischemic stroke has not been determined. We evaluated the influence of iron stores, measured as serum ferritin, on the outcome of acute cerebral infarct.

METHODS

Admission and fasting glycemia, glycosylated hemoglobin, serum cortisol, serum ferritin, and 24-hour urinary free cortisol levels were measured on the first day of hospitalization in 67 patients admitted with an acute ischemic stroke of less than 24 hours' duration. Patients were classified into two groups according to their Canadian Stroke Scale (CSS) score on day 30: good outcome group (alive and CSS score > 7 points) and poor outcome group (dead or CSS score < or = 7 points).

RESULTS

Thirty-three patients (49%) had good outcome and 34 (51%) poor outcome. Fasting glycemia (P = .001), serum cortisol (P < .001), and urinary free cortisol (P = .001) but not admission glycemia and glycosylated hemoglobin had higher levels in patients with poor outcome. Serum ferritin values were greater in the poor outcome group (218 +/- 156 micrograms/L versus 133 +/- 125 micrograms/L; P = .004), and a correlation between ferritin values and degree of worsening or improvement of the CSS score on day 30 was found (P = .002). Serum cortisol (odds ratio [OR], 6.7; 95% confidence interval [CI], 1.7 to 26), fasting glycemia (OR, 5.4; 95% CI, 1.2 to 24), and serum ferritin (OR, 4.6; 95% CI, 1.1 to 19) were independently related to poor outcome in a logistic regression analysis.

CONCLUSIONS

High serum ferritin levels within the first 24 hours of hospitalization for an acute ischemic stroke are related to a poor prognosis, independent of the stress response. More research is needed to determine the origin of increased serum ferritin levels and the therapeutic implications.

Iron stores are not associated with acute myocardial infarction

BACKGROUND

This study evaluated the relation between body iron stores and coronary artery disease. It has been suggested that total body iron stores are an independent risk factor for acute myocardial infarction (AMI).

METHODS AND RESULTS

Our study population consisted of 46,932 members of a prepaid health plan who were > or = 30 years old and who received a standard health check between 1969 and 1971. Blood collected during this examination was analyzed for serum iron and total iron-binding capacity. Transferrin saturation (TS), calculated as (serum iron/total iron-binding capacity) x 100, was categorized as low (< or = 10%), normal (11% to 61%), or elevated (> or = 62%). Hospital stays for AMI were identified from the health plan's computerized discharge records for its Northern California Region through December 31, 1991. Mean follow-up time was 14.1 years. During the follow-up period, 969 men and 871 women had an AMI-related hospital stay. Analysis of AMI-related hospital stays was performed overall and by sex. Age-adjusted incidence rates were obtained for each TS level, and proportional hazards regression models were used to assess the significance of TS as a risk factor for AMI, controlling for other known coronary disease risk factors. Our results did not show iron deficiency as defined by low TS to be protective against AMI. Subjects with increased iron stores indicated by TS > or = 62% had a relative risk for AMI of 1.3, which was not statistically significant.

CONCLUSIONS

Our observations do not support the hypothesis that coronary artery disease risk is related to iron stores.