Association between increased iron stores and impaired endothelial function in patients with hereditary hemochromatosis

Spatial and temporal dynamics of the endothelium

The endothelium is a highly metabolically active organ that is involved in many physiological processes, including the control of vasomotor tone, barrier function, leukocyte adhesion and trafficking, inflammation, and hemostasis. Endothelial cell phenotypes are differentially regulated in space and time. Endothelial cell heterogeneity has important implications for developing strategies in basic research, diagnostics and therapeutics. The goals of this review are to: (i) consider mechanisms of endothelial cell heterogeneity; (ii) discuss the bench-to-bedside gap in endothelial biomedicine; (iii) revisit definitions for endothelial cell activation and dysfunction; and (iv) propose new goals in diagnosis and therapy. Finally, these themes will be applied to an understanding of vascular bed-specific hemostasis.

Endothelial biomedicine: its status as an interdisciplinary field, its progress as a basic science, and its translational bench-to-bedside gap

The endothelium, a layer of endothelial cells lining the luminal surface of all blood vessels, functions as a highly metabolically active organ spatially distributed throughout the body. Despite enormous advances in our understanding of endothelial cell biology, little awareness of this organ reaches clinical practice. The present study aims to document the extent and scope of the bench-to-bedside gap in endothelial biomedicine, and to offer hypotheses to explain the gaping chasm. A PubMed search using keywords "endothelial cells" and "endothelium" yielded over 90,000 publications, increasing exponentially over the past decade. A Scirus search without date restriction returned journal results for the endothelium not greatly fewer than for the epithelium. A survey of representative vascular biology meetings revealed a high percentage of talks related to the endothelium. The number of grants awarded by the National Institutes of Health for studies in endothelial cell biology continues to steadily increase. At the bedside, however, few clinicians give consideration to the health of the endothelium. A survey of the major medical textbooks revealed a paucity of index entries for "endothelial cells" or "endothelium." The endothelium does not offer itself for inspection, palpation, percussion, and/or auscultation. No convenient blood tests measure endothelial function. The authors propose to explain the bench-to-bedside gap in endothelial biomedicine as a function of (1) historical constraints, (2) the unseen and diffuse nature of the cell layer, (3) the complexity of the system, and (4) its adaptability. Until the bench-to-bedside gap closes, the enormous potential of the endothelium as a diagnostic, preventive, and therapeutic target will remain largely untapped.

Oxidized low-density lipoprotein, iron stores, and haptoglobin polymorphism

BACKGROUND

In vitro experimental studies demonstrated that iron promotes free radical-induced low-density lipoprotein (LDL) oxidation.

OBJECTIVE

To test the hypothesis that circulating oxidized LDL (oxLDL) levels might be associated with body iron stores (serum ferritin) and iron-related genetic markers (hemochromatosis gene C282Y mutation, haptoglobin polymorphism).

METHODS

We investigated 381 (176 males, 205 females, age 45 +/- 6 years) healthy Caucasians. Serum oxLDL, assayed by a mAb-4E6-based enzyme-linked immunosorbent assay (ELISA), was expressed as oxLDL/LDL ratio to adjust for serum LDL-cholesterol concentration. Hemochromatosis gene C282Y mutation analysis was performed by a Taqman-based polymerase chain reaction (PCR) assay. Haptoglobin (Hp) phenotypes (Hp 1-1, Hp 2-1, Hp 2-2) were determined by starch gel electrophoresis.

RESULTS

In stepwise multivariate regression analysis, gender (P < 0.0001), current smoking (P < 0.0001), HDL-cholesterol (P = 0.0001), ferritin (P = 0.0051), body mass index (BMI) (P = 0.0063), and Hp phenotype (P = 0.0331) independently predicted oxLDL/LDL ratio in the total group. In men, smoking (P < 0.0001), ferritin (P = 0.0052), Hp phenotype (P = 0.0063), and HDL-cholesterol (P = 0.0127) were independent determinants of oxLDL/LDL ratio. In women, only body mass index (P < 0.0001), HDL-cholesterol (P = 0.0005), and smoking (P = 0.0025) were significantly associated with oxLDL/LDL ratio. The C282Y mutation (wild-type versus C282Y heterozygotes) was not associated with oxLDL/LDL ratio in both sexes.

CONCLUSION

Serum ferritin concentration and Hp polymorphism are independently associated with circulating oxLDL levels in males.

Implementation of an iron reduction protocol in patients with peripheral vascular disease: VA cooperative study no. 410: the Iron (Fe) and Atherosclerosis Study (FeAST)

BACKGROUND

Iron accumulates imperceptibly over time in adults because intake exceeds loss and because no physiologic mechanism exists for excreting levels that may be toxic. Levels of stored iron represented by the serum ferritin concentration have been implicated in the pathogenesis of vascular (and other) diseases, but the role of such stored iron remains controversial. Our hypothesis was that reduction in body iron stores to levels typical of children and premenopausal women (corresponding to ferritin levels of approximately 25 ng/mL) would alter morbidity and mortality rates in patients with advanced peripheral vascular disease.

METHODS AND RESULTS

A randomized, single-blinded, clinical trial of graded reduction of iron stores by controlled phlebotomy was undertaken in patients with advanced peripheral vascular disease. Details of implementation of the protocol for testing this unusual experimental intervention are reported.

CONCLUSIONS

A methodology is described for testing the concept that reduction of body iron stores (while avoiding iron deficiency) may alter disease outcomes. This methodology appears to be suitable for further testing to determine whether levels of iron stores presumed to be pathologic contribute to disease initiation or progression.

Dose-dependent effect of parenteral iron therapy on bleomycin-detectable iron in immune apheresis patients

BACKGROUND

Iron deficiency and anemia are commonly encountered in patients with autoimmune diseases undergoing immune apheresis. This makes erythropoietin and iron substitution necessary in most patients. However, intravenous iron therapy may result in an increase of potentially toxic nontransferrin-bound iron.

METHODS

We examined the effect of 50 mg or 100 mg of iron (III) sucrose on bleomycin-detectable iron (BDI) in immune apheresis patients. Six patients with autoimmune disorders and normal kidney function were enrolled. Before and after the injection of 50 mg or 100 mg of iron (III) sucrose, BDI was measured in serum samples at five different time points.

RESULTS

There was no BDI traceable before injection of iron (III) sucrose. BDI was present in serum of all patients after the administration of 100 mg of iron (III) sucrose in concentrations up to 0.49 micromol/L. In contrast, only one patient showed BDI at a concentration of 0.16 micromol/L after the administration of 50 mg of iron (III) sucrose.

CONCLUSION

We conclude that if parenteral iron is administered after apheresis treatment, despite the equal tolerability, use of 50 mg of iron (III) sucrose is superior to 100 mg of iron (III) sucrose in avoiding the formation of potentially toxic nontransferrin-bound iron.

Endothelium as an organ system

The endothelium is a highly dynamic cell layer that is involved in a multitude of physiologic functions, including the control of vasomotor tone, the trafficking of cells and nutrients, the maintenance of blood fluidity, and the growth of new blood vessels. Over the past several decades, advances in basic research of the endothelium have far outstripped those in the clinic. One explanation for this growing bench-to-bedside chasm relates to the inflexible and largely outdated nature of the present-day medical infrastructure. The constraints of medical subspecialization have created a conceptual blind spot, namely, the inability to appreciate the endothelium for what it is: a cell layer that is teeming with life, every bit as active as any other organ in the body. The overall goal of this review is to bring the endothelium "to life" and to argue that future breakthroughs in biomedicine are contingent on acceptance of the endothelium as a bona fide organ system.

Is blood donation induced low iron status associated with favourable levels of OxLDL, s-ICAM-1, sVCAM-1 and vWF-antigen in healthy men

The potential effect of iron depletion by blood donation and its relevance to cardiovascular diseases are still under debate. Markers of vascular integrity are increasingly applied in investigations of atherothrombotic diseases. In this study, we investigated whether a lower iron status through blood donation was associated with markers of vascular integrity (circulating oxidised LDL, sICAM-1, sVCAM-1 and vWF-antigen) by comparing healthy male voluntary donors to non-donors, taking into account differences in baseline characteristics. Two fasting blood samples were collected within 1 week from 41 donors and 39 non-donors. The iron status was estimated by measuring the concentration of plasma iron, ferritin, haemoglobin and hematocrit. The markers of iron status were all significantly lower in donors compared to non-donors, especially for ferritin concentrations. However, the lower iron status by blood donation was not reflected in the concentrations of OxLDL, sICAM-1, sVCAM-1 and vWF-antigen in men after adjustment for BMI and ratio total/HDL cholesterol. In order to avoid possible selection-bias related to donorship, we have additionally investigated the difference in marker concentrations within the non-donors, comparing low- and high-ferritin concentrations. This analysis suggests that ferritin concentration is not associated with in vivo LDL oxidation.

Association Between High Serum Ferritin Levels and Carotid Atherosclerosis in the Study of Health in Pomerania (SHIP)

BACKGROUND AND PURPOSE

Several studies have provided evidence for a relationship between body iron load and cardiovascular disease. We analyzed the association of serum ferritin levels with carotid atherosclerosis.

METHODS

We assessed intima-media thickness and plaque prevalence in the carotid arteries by high-resolution ultrasound among 2443 participants (1200 women; age, 45 to 79 years) in the Study of Health in Pomerania (SHIP), a population-based study in northeast Germany.

RESULTS

In multivariate analysis, serum ferritin levels were not independently associated with carotid intima-media thickness among women or men. In contrast, the relationship between serum ferritin levels and carotid plaque prevalence was significant among men (odds ratio per 1-SD increase of serum ferritin levels, 1.33; 95% confidence interval, 1.08 to 1.44) yet not among women (odds ratio, 1.29; 95% confidence interval, 0.98 to 1.75). However, both men and women showed a dose-response relation between serum ferritin levels and carotid atherosclerosis in which higher serum ferritin levels were associated with greater odds ratios for carotid plaque prevalence. Additionally, there was an interaction of serum ferritin levels with low-density lipoprotein (LDL) cholesterol (P=0.039) among men in which the association of serum ferritin levels with carotid plaque prevalence became stronger with increasing LDL cholesterol levels.

CONCLUSIONS

Our study identified a relationship between serum ferritin levels and carotid atherosclerosis that was potentiated by LDL cholesterol. This relationship adds support to the hypothesis of a link between iron and cardiovascular disease.

Impairment of Transendothelial Leukocyte Migration by Iron Complexes

ABSTRACT. Although iron sucrose and iron gluconate are generally well tolerated in patients who are treated for renal anemia, recent clinical studies and cell culture experiments suggested significant toxicity and long-term side effects arising from the use of these iron complexes. Because of the possible role of iron in infection or cardiovascular disease, it was theorized that parenteral iron compounds influence endothelial and PMN interactionin vitro. A well-established double-chamber method was used to assess the effect of different concentrations of iron sucrose and iron gluconate (1, 25, 50, and 100 μg/ml) on the transendothelial migration of PMN. Preincubation of PMN and endothelial cells as well as preincubation of PMN alone with 25, 50, or 100 μg/ml iron resulted in a significant decrease in PMN migration. In contrast, after incubation of the endothelial cells alone with iron, no reduction in the transendothelial migration of PMN was observed. Preincubation of PMN and/or endothelial cells with 1 μg/ml iron did not lead to any decrease in the rate of migrated PMN. The only significant change in experiments with 1 μg/ml was an increase in PMN migration after preincubation of endothelial cells and PMN with iron gluconate. A four-way ANOVA showed a significant effect of the iron concentration (P< 0.000001), of type of iron complex (P< 0.005), of the preincubation of endothelial cell (P< 0.001), and of the preincubation of PMN with iron (P< 0.000001) on PMN diapedesis. It is concluded that iron sucrose and iron gluconate cause a significant inhibition of transendothelial migration of PMN. E-mail: Guerkan.Sengoelge@univie.ac.at

Chronic iron administration increases vascular oxidative stress and accelerates arterial thrombosis

BACKGROUND

Iron overload has been implicated in the pathogenesis of ischemic cardiovascular events. However, the effects of iron excess on vascular function and the thrombotic response to vascular injury are not well understood.

METHODS AND RESULTS

We examined the effects of chronic iron dextran administration (15 mg over 6 weeks) on thrombosis, systemic and vascular oxidative stress, and endothelium-dependent vascular reactivity in mice. Thrombus generation after photochemical carotid artery injury was accelerated in iron-loaded mice (mean time to occlusive thrombosis, 20.4+/-8.5 minutes; n=10) compared with control mice (54.5+/-35.5 minutes, n=10, P=0.009). Iron loading had no effect on plasma clotting, vessel wall tissue factor activity, or ADP-induced platelet aggregation. Acute administration of dl-cysteine, a reactive oxygen species scavenger, completely abrogated the effects of iron loading on thrombus formation, suggesting that iron accelerated thrombosis through a pro-oxidant mechanism. Iron loading enhanced both systemic and vascular reactive oxygen species production. Endothelium-dependent vasorelaxation was impaired in iron-loaded mice, indicating reduced NO bioavailability.

CONCLUSIONS

Moderate iron loading markedly accelerates thrombus formation after arterial injury, increases vascular oxidative stress, and impairs vasoreactivity. Iron-induced vascular dysfunction may contribute to the increased incidence of ischemic cardiovascular events that have been associated with chronic iron overload.