J. J. M. Marx

Ferric saccharate induces oxygen radical stress and endothelial dysfunction in vivo

Background u2002Intravenous iron supplementation is used widely in haemodialysis patients. However, nontransferrin‐bound iron (NTBI), which increases after intravenous supplementation of ferric saccharate, has been suggested to act as a catalytic agent in oxygen radical formation in vitro and may thus contribute to endothelial impairment in vivo.

Non‐transferrin‐bound iron is present in serum of hereditary haemochromatosis heterozygotes

Hereditary haemochromatosis (HH) is a common autosomal recessive disease. Recently, HH heterozygosity has been identified as an independent risk factor for myocardial infarction and cardiovascular mortality. Iron may play an important role in atherogenesis by catalyzing peroxidation of low‐density‐lipoprotein (LDL), an essential step in atherogenesis. In iron overload conditions, non‐transferrin‐bound iron (NTBI) is found in serum, which can catalyze lipid peroxidation. We investigated whether sera of HH heterozygotes contain more NTBI than sera of normal controls.

Listeria monocytogenes meningitis and decreased phagocytosis associated with iron overload.

A patient with Listeria monocytogenes meningitis was found to have idiopathic haemochromatosis and monocytes with reduced phagocytic capacity. The phagocytic function recovered completely after a series of therapeutic phlebotomies. In-vitro iron had a deleterious effect on the phagocytic capacity of monocytes and granulocytes. These findings show that iron overload in the host can increase susceptibility to L monocytogenes infection not only by increasing the virulence of the organism but also by reducing the phagocytic capacity of the monocytes.

Nontransferrin‐bound iron in the plasma of haemodialysis patients after intravenous iron saccharate infusion

Background Many haemodialysis patients treated with recombinant human erythropoietin (r‐HuEPO) receive intravenous iron supplementation on a regular basis. It has been shown previously that this may result in a transient ‘oversaturation’ of transferrin.

Iron and inflammatory bowel disease

Both anaemia of iron deficiency and anaemia of chronic disease are frequently encountered in inflammatory bowel disease. Anaemia of iron deficiency is mostly due to inadequate intake or loss of iron. Anaemia of chronic disease probably results from decreased erythropoiesis, secondary to increased levels of proinflammatory cytokines, reactive oxygen metabolites and nitric oxide.

Inhibition of Human Immunodeficiency Virus Type 1 Replication in Human Mononuclear Blood Cells by the Iron Chelators Deferoxamine, Deferiprone, and Bleomycin

Replication of human immunodeficiency virus type 1 (HIV-1) can be influenced by iron. Hence, decreasing the availability of iron may inhibit HIV-1 replication. Deferoxamine and deferiprone, both forming catalytically inactive iron-chelator complexes, and bleomycin, by use of which iron catalyzes oxidative nucleic acid destruction, were investigated. Expression of p24 antigen in human monocyte-derived macrophages and peripheral blood lymphocytes (PBL) was reduced by all 3 iron chelators. In PBL, p24 reduction was mirrored by a decrease in proliferation after incubation with deferoxamine or deferiprone, suggesting that viral inhibition is closely linked to a decrease in cellular proliferation. In contrast, clinically relevant bleomycin concentrations reduced p24 levels by approximately 50% without affecting proliferation. When deferoxamine and the nucleoside analogue dideoxyinosine were used in combination, they acted synergistically in inhibiting HIV-1 replication. These observations suggest that iron chelators with different mechanisms of action could be of additional benefit in antiretroviral combination therapy.

Serum Ferritin Is a Risk Factor for Stroke in Postmenopausal Women

Background and Purpose— Iron is an essential element for the human body. It has, however, been suggested that excessive iron stores may increase the risk of vascular disease. So far, epidemiologic studies on stroke are sparse. Methods— We studied the association between iron status and stroke risk in a population-based cohort of 11 471 Dutch postmenopausal women between 49 and 70 years of age. Women were included between 1993 and 1997 and followed up until January 1, 2000, for cerebrovascular events. We conducted a case-cohort study by using all stroke cases (n=63) and a random sample of the baseline cohort (n=1134). Serum ferritin, serum iron, and transferrin saturation were measured as markers of iron status. A weighted Cox proportional-hazards model was used to estimate crude and multivariate-adjusted hazard ratios for tertiles of different iron parameters in relation to stroke. Results— In a multivariate model, the highest tertile of serum ferritin concentration was associated with an increased risk of stroke (hazard ratio [HR], 1.45; 95% confidence interval [CI], 0.87 to 2.42) compared with the lowest tertile. For ischemic stroke, the increase was more pronounced (HR, 2.23; 95% CI, 1.05 to 4.73) and reached statistical significance. Conclusions— Neither serum iron nor transferrin saturation was associated with an increased stroke risk. However, higher serum ferritin concentrations in postmenopausal women are associated with an increased risk of ischemic stroke.

Endothelial activation and induction of monocyte adhesion by nontransferrin-bound iron present in human sera

Nontransferrin‐bound iron (NTBI) has been detected in iron overload diseases. This form of iron may exert pro‐oxidant effects and modulate cellular function and inflammatory response. The present study has aimed to investigate the effects of serum NTBI on monocyte adherence to endothelium. Measured by a recently developed high‐throughput fluorescence‐based assay, serum NTBI was found to be higher in both homozygotes of HFE C282Y mutation of hereditary hemochromatosis (7.9±0.6 μM, n=9, P<0.001) and heterozygotes (4.0±0.5 μM, n=8, P<0.001), compared with controls (1.6±0.2 μM, n=21). The effects of these sera on monocyte adhesion and endothelial activation were examined. Adhesion of normal human monocytes to C282Y homozygote‐ and heterozygote‐serum‐treated human umbilical vein endothelial cells was higher (25.0±0.9 and 22.1±0.7%, respectively) compared with controls (17.6±0.5%, both P<0.001). For the three groups combined, the expression of adhesion molecules, ICAM‐1, VCAM‐1, and Eselectin, was positively correlated to NTBI levels but not to the inflammatory marker C‐reactive protein. Furthermore, accumulation of intracellular labile iron and oxidative radicals within the cells due to NTBI was evidenced. Finally, counteraction of NTBI‐induced endothelial activation was observed using iron chelators. These findings therefore identify a physiological function of NTBI in monocyte‐endothelial interactions that may also contribute to the development of atherosclerosis and neurodegenerative diseases.

Non–Transferrin-Bound Iron and Risk of Coronary Heart Disease in Postmenopausal Women

Background— Epidemiological studies aimed at correlating coronary heart disease (CHD) with serum ferritin levels have thus far yielded inconsistent results. We hypothesized that a labile iron component associated with non–transferrin-bound iron (NTBI) that appears in individuals with overt or cryptic iron overload might be more suitable for establishing correlations with CHD. Methods and Results— We investigated the relation of NTBI, serum iron, transferrin saturation, and serum ferritin with risk of CHD and acute myocardial infarction (AMI). The cohort used comprised a population-based sample of 11 471 postmenopausal women aged 49 to 70 years at enrollment in 1993 to 1997. During a median follow-up of 4.3 years (quartile limits Q1 to Q3: 3.3 to 5.4), 185 CHD events were identified, including 66 AMI events. We conducted a case-cohort study using all CHD cases and a random sample from the baseline cohort (n=1134). A weighted Cox proportional hazards model was used to estimate hazard ratios for tertiles of iron variables in relation to CHD and AMI. Adjusted hazard ratios of women in the highest NTBI tertile (range 0.38 to 3.51) compared with the lowest (range −2.06 to −0.32) were 0.84 (95% confidence interval 0.61 to 1.16) for CHD and 0.47 (95% confidence interval 0.31 to 0.71) for AMI. The results were similar for serum iron, transferrin saturation, and serum ferritin. Conclusions— Our results show no excess risk of CHD or AMI within the highest NTBI tertile compared with the lowest but rather seem to demonstrate a decreased risk. Additional studies are warranted to confirm our findings.

Intracellular Labile Iron Modulates Adhesion of Human Monocytes to Human Endothelial Cells

Objective—Elevated iron stores and high plasma iron concentration have been linked to an increased risk of atherosclerosis. Iron may thereby affect the interaction of monocytes to endothelium, an initial event in the formation of atherosclerotic plaques. Methods and Results—Addition of 10 &mgr;mol/L non–transferrin-bound iron to the incubation medium caused a 2-fold increase in monocyte adhesion to human umbilical vein endothelial cells (HUVECs). A concordant increase in the expression of the following adhesion molecules was observed: vascular cell adhesion molecule-1, intercellular adhesion molecule-1, and endothelial selectin on HUVECs as well as very late antigen-4, and lymphocyte function–associated antigen-1 on monocytes. The inclusion of either deferiprone or salicylaldehyde isonicotinoylhydrazone counteracted these effects. Intracellular iron chelation by deferoxamine was completed only after 10 hours of incubation, shown by reversal of iron-quenched intracellular calcein signal, and concurrently the effects of iron were blunted. The membrane-impermeable chelator, diethylenetriamine pentaaceticacid, failed to negate iron effects, even after 48 hours of treatment. Furthermore, only membrane-permeable superoxide or hydroxyl radical scavengers were capable of preventing HUVEC activation by iron. Conclusions—Non–transferrin-bound iron increases the level of intracellular labile iron, which promotes monocyte recruitment to endothelium and may thereby contribute to the pathogenesis of atherosclerosis. Iron-induced adhesion molecule expression was observed, and this event may involve the production of oxygen radicals.