Serum Hepcidin and Macrophage Iron Correlate With MCP-1 Release and Vascular Damage in Patients With Metabolic Syndrome Alterations

Elevated Hepcidin Expression in Human Carotid Atheroma: Sex-Specific Differences and Associations with Plaque Vulnerability

Hepcidin is upregulated by increased body iron stores and inflammatory cytokines. It is associated with cardiovascular events, arterial stiffness, and increased iron accumulation in human atheroma with hemorrhage. However, it is unknown whether the expression of hepcidin in human carotid plaques is related to plaque severity and whether hepcidin expression differs between men and women. Carotid samples from 58 patients (38 males and 20 females) were immunostained with hepcidin, macrophages, ferritin, and transferrin receptor. Immunocytochemistry of hepcidin was performed on THP-1 macrophages exposed to iron or 7betahydroxycholesterol. Hepcidin expression significantly increases with the progression of human atherosclerotic plaques. Plaques of male patients have significantly higher levels of hepcidin. Expressions of hepcidin are significantly correlated with the accumulation of CD68-positive macrophages and transferrin receptor 1 (TfR1) and apoptosis. In vitro, hepcidin is significantly increased in macrophages exposed to iron and moderately increased following 7-oxysterol treatment. In the cultured cells, suppression of hepcidin protected against macrophage cell death, lysosomal membrane permeabilization, and oxidative stress. Hepcidin may play a crucial role in the development and progression of atherosclerosis. The differential expression of hepcidin in male and female patients and its significant correlations with plaque severity, highlight the potential of hepcidin as a biomarker for risk stratification and therapeutic targeting in atherosclerosis.

Moderate physical activity against effects of short-term PM2.5 exposure on BP via myokines-induced inflammation

Exposure to PM2.5 increases blood pressure (BP) and cardiovascular morbidity and mortality. We conducted a randomized controlled panel study in Shijiazhuang, China among 55 healthy college students randomly assigned to either the control (CON) or SPORTS group with intervention of 2000 m jogging in 20 min for 3 times in 4 days, and 3-round health examinations from November 15, 2020 to December 6, 2020. We aimed to evaluate whether moderate physical activity (PA) protected BP health against PM2.5 exposure and explore potential mechanisms through myokines and inflammation. Individual PM2.5 exposure was calculated based on outdoor and indoor PM2.5 concentration monitoring data as well as time-activity diary of each subject. In the CON group, the exposure-response curve for SBP was linear with a threshold concentration of approximately 31 μg/m3, while an increment of SBP level was 4.38 mm Hg (95%CI: 0.17 mm Hg, 8.59 mm Hg) at lag03 for each 10-μg/m3 increase in PM2.5, using linear mixed-effect models. For inflammatory indicators, PM2.5 exposure was associated with significant increases in eosinophil counts and proportion in CON group, but decreases in MCP-1 and TNF-α in SPORTS group. Meanwhile, higher myokines including CLU and IL-6 were observed in SPORTS group compared to the CON group. Further mediation analyses revealed that eosinophil counts mediated the elevated BP in CON group, whereas MCP-1 and TNF-α were also crucial mediating cytokines for the SPORTS group, as well as CLU and IL-6 acted as mediators on BP and inflammation indicators in SPORTS group. This study suggests that moderate PA could counteract the elevated BP induced by PM2.5 exposure via myokines-suppressed inflammation pathways.

Dietary iron overload enhances Western diet induced hepatic inflammation and alters lipid metabolism in rats sharing similarity with human DIOS

Hepatic iron overload is often concurrent with nonalcoholic fatty liver disease (NAFLD). Dysmetabolic iron overload syndrome (DIOS) is characterized by an increase in the liver and body iron stores and metabolic syndrome components. Increasing evidences suggest an overlap between NAFLD with iron overload and DIOS; however, the mechanism how iron is involved in their pathogenesis remains unclear. Here we investigated the role of iron in the pathology of a rat model of NAFLD with iron overload. Rats fed a Western (high-fat and high-fructose) diet for 26 weeks represented hepatic steatosis with an increased body weight and dyslipidemia. Addition of dietary iron overload to the Western diet feeding further increased serum triglyceride and cholesterol, and enhanced hepatic inflammation; the affected liver had intense iron deposition in the sinusoidal macrophages/Kupffer cells, associated with nuclear translocation of NFκB and upregulation of Th1/M1-related cytokines. The present model would be useful to investigate the mechanism underlying the development and progression of NAFLD as well as DIOS, and to elucidate an important role of iron as one of the "multiple hits" factors.

Vascular Aging and Damage in Patients with Iron Metabolism Disorders

Vascular aging is a physiological, multifactorial process that involves every type of vessel, from large arteries to microcirculation. This manifests itself as impaired vasomotor function, altered secretory phenotype, deteriorated intercellular transport function, structural remodeling, and aggravated barrier function between the blood and the vascular smooth muscle layer. Iron disorders, particularly iron overload, may lead to oxidative stress and, among other effects, vascular aging. The elevated transferrin saturation and serum iron levels observed in iron overload lead to the formation of a non-transferrin-bound iron (NTBI) fraction with high pro-oxidant activity. NTBI can induce the production of reactive oxygen species (ROS), which induce lipid peroxidation and mediate iron-related damage as the elements of oxidative stress in many tissues, including heart and vessels' mitochondria. However, the available data make it difficult to precisely determine the impact of iron metabolism disorders on vascular aging; therefore, the relationship requires further investigation. Our study aims to present the current state of knowledge on vascular aging in patients with deteriorated iron metabolism.

Short-term ozone exposure and metabolic status in metabolically healthy obese and normal-weight young adults: A viewpoint of inflammatory pathways

Unhealthy metabolic status increases risks of cardiovascular and other diseases. This study aims to explore whether there is a link between O₃ and metabolic health indicators through a viewpoint of inflammatory pathways. 49 metabolically healthy normal-weight (MH-NW) and 39 metabolically healthy obese (MHO) young adults aged 18-26 years were recruited from a panel study with three visits. O₃ exposure were estimated based on fixed-site environmental monitoring data and time-activity diary for each participant. Compared to MH-NW people, MHO people were more susceptible to the adverse effects on metabolic status, including blood pressure, glucose, and lipid indicators when exposed to O₃. For instance, O₃ exposure was associated with significant decreases in high-density lipoprotein cholesterol (HDL-C), and increases in C-peptide and low-density lipoprotein cholesterol (LDL-C) among MHO people, while only weaker changes in HDL-C and LDL-C among MH-NW people. Mediation analyses indicated that leptin mediated the metabolic health effects in both groups, while eosinophils and MCP-1 were also important mediating factors for the MHO people. Although both with a metabolically healthy status, compared to normal-weight people, obese people might be more susceptible to the negative effects of O₃ on metabolic status, possibly through inflammatory indicators such as leptin, eosinophils, and MCP-1.

Does iron overload in metabolic syndrome affect macrophage profile? A case control study

AIMS

Dysmetabolic iron overload syndrome (DIOS) is common but the clinical relevance of iron overload is not understood. Macrophages are central cells in iron homeostasis and inflammation. We hypothesized that iron overload in DIOS could affect the phenotype of monocytes and impair macrophage gene expression.

METHODS

This study compared 20 subjects with DIOS to 20 subjects with metabolic syndrome (MetS) without iron overload, and 20 healthy controls. Monocytes were phenotyped by Fluorescence-Activated Cell Sorting (FACS) and differentiated into anti-inflammatory M2 macrophages in the presence of IL-4. The expression of 38 genes related to inflammation, iron metabolism and M2 phenotype was assessed by real-time PCR.

RESULTS

FACS showed no difference between monocytes across the three groups. The macrophagic response to IL-4-driven differentiation was altered in four of the five genes of M2 phenotype (MRC1, F13A1, ABCA1, TGM2 but not FABP4), in DIOS vs Mets and controls demonstrating an impaired M2 polarization. The expression profile of inflammatory genes was not different in DIOS vs MetS. Several genes of iron metabolism presented a higher expression in DIOS vs MetS: SCL11A2 (a free iron transporter, +76 %, p = 0.04), SOD1 (an antioxidant enzyme, +27 %, p = 0.02), and TFRC (the receptor 1 of transferrin, +59 %, p = 0.003).

CONCLUSIONS

In DIOS, macrophage polarization toward the M2 alternative phenotype is impaired but not associated with a pro-inflammatory profile. The up regulation of transferrin receptor 1 (TFRC) in DIOS macrophages suggests an adaptive role that may limit iron toxicity in DIOS.

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.

In-depth review: is hepcidin a marker for the heart and the kidney?

Iron is an essential trace element involved in oxidation-reduction reactions, oxygen transport and storage, and energy metabolism. Iron in excess can be toxic for cells, since iron produces reactive oxygen species and is important for survival of pathogenic microbes. There is a fine-tuning in the regulation of serum iron levels, determined by intestinal absorption, macrophage iron recycling, and mobilization of hepatocyte stores versus iron utilization, primarily by erythroid cells in the bone marrow. Hepcidin is the major regulatory hormone of systemic iron homeostasis and is upregulated during inflammation. Hepcidin metabolism is altered in chronic kidney disease. Ferroportin is an iron export protein and mediates iron release into the circulation from duodenal enterocytes, splenic reticuloendothelial macrophages, and hepatocytes. Systemic iron homeostasis is controlled by the hepcidin-ferroportin axis at the sites of iron entry into the circulation. Hepcidin binds to ferroportin, induces its internalization and intracellular degradation, and thus inhibits iron absorption from enterocytes, and iron release from macrophages and hepatocytes. Recent data suggest that hepcidin, by slowing or preventing the mobilization of iron from macrophages, may promote atherosclerosis and may be associated with increased cardiovascular disease risk. This article reviews the current data regarding the molecular and cellular pathways of systemic and autocrine hepcidin production and seeks the answer to the question whether changes in hepcidin translate into clinical outcomes of all-cause and cardiovascular mortality, and cardiovascular and renal end-points.

Relationship between serum hepcidin levels and cardiovascular disease in patients with maintenance hemodialysis

Background

To investigate the serum level of hepcidin and its relationship with cardiovascular disease (CVD) in maintenance hemodialysis (MHD) patients.

Methods

Blood was obtained from 75 MHD patients before undergoing hemodialysis and 20 healthy controls. Serum hepcidin, advanced oxidation protein products (AOPP) and interleukin (IL)-6 were measured by enzyme-linked immunosorbant assay (ELISA). Spearman correlation, and binary logistic regression linear regression analyses were used to assess the relationship between serum hepcidin and other parameters.

Results

The serum level of hepcidin, AOPP and IL-6 was significantly up-regulated in MHD patients compared with the control (P < 0.05). Furthermore, serum hepcidin levels in patients with CVD were higher than those in patients without CVD (P < 0.05). In all MHD patients, serum hepcidin level was correlated positively with erythropoietin (EPO) dose per week (ρ = 0.251, P = 0.030), EPO resistance index (ρ = 0.268, P = 0.020), ferritin (ρ = 0.814, P < 0.001), transferin saturation (TSAT, ρ = 0.263, P = 0.023), AOPP (ρ = 0.280, P = 0.049), high sensitive C reactive protein (ρ = 0.151, P = 0.006), IL-6 (ρ = 0.340, P = 0.003) and left ventricular mass index (LVMI, ρ = 0.290, P = 0.033). Moreover, it was negatively correlated with serum pre-albumin (ρ = -0.266, P = 0.021), total iron-binding capacity (TIBC, ρ = -0.458, P < 0.001), unsaturated iron-binding capacity (UIBC, ρ = -0.473, P < 0.001) and transferrin (ρ = -0.487, P < 0.001). Linear regression analysis showed that ferritin (β = 0.708, P < 0.001), TIBC (β = -0.246, P = 0.032) and IL-6 (β = 0.209, P = 0.041) were independently associated with hepcidin. Results of binary logistic regression analysis suggested that higher serum hepcidin level (>249.2 ng/mL) was positively and independently related to CVD (OR = 1.32, 95% CI [1.20-9.56], P = 0.043).

Conclusions

Serum hepcidin level is associated with CVD in MHD patients, indicating that hepcidin may be a novel biomarker and therapeutic target for CVD.

The role of hepcidin and iron homeostasis in atherosclerosis

Atherosclerotic cardiovascular disease is a major burden on global health and a leading cause of death worldwide. The pathophysiology of this chronic disease is complex, involving inflammation, lipoprotein oxidation and accumulation, plaque formation, and calcification. In 1981, Dr. Jerome Sullivan formulated the 'Iron Hypothesis', suggesting that higher levels of stored iron promote cardiovascular diseases, whereas iron deficiency may have an atheroprotective effect. This hypothesis has stimulated research focused on clarifying the role of iron in the development of atherosclerosis. However, preclinical and clinical studies have produced contradictory results and the observation that patients with hemochromatosis do not appear to have an increased risk of atherosclerosis seemed incongruous with Sullivan's initial hypothesis. The 'paradox' of systemic iron overload not being accompanied by an increased risk for atherosclerosis led to a refinement of the iron hypothesis focusing on intracellular macrophage iron. More recent in vitro and animal studies have elucidated the complex signaling pathways regulating iron, with a particular focus on hepcidin, the master regulator of body iron homeostasis. Bone morphogenetic protein (BMP) signaling is the major pathway that is required for induction of hepcidin expression in response to increasing levels of iron. Strong links between iron homeostasis, BMP signaling, inflammation and atherosclerosis have been established in both mechanistic and human studies. This review summarizes the current understanding of the role of iron homeostasis and hepcidin in the development of atherosclerosis and discusses the BMP-hepcidin-ferroportin axis as a novel therapeutic target for the treatment of cardiovascular disease.

The multifaceted role of iron in renal health and disease

Iron is an essential element that is indispensable for life. The delicate physiological body iron balance is maintained by both systemic and cellular regulatory mechanisms. The iron-regulatory hormone hepcidin assures maintenance of adequate systemic iron levels and is regulated by circulating and stored iron levels, inflammation and erythropoiesis. The kidney has an important role in preventing iron loss from the body by means of reabsorption. Cellular iron levels are dependent on iron import, storage, utilization and export, which are mainly regulated by the iron response element-iron regulatory protein (IRE-IRP) system. In the kidney, iron transport mechanisms independent of the IRE-IRP system have been identified, suggesting additional mechanisms for iron handling in this organ. Yet, knowledge gaps on renal iron handling remain in terms of redundancy in transport mechanisms, the roles of the different tubular segments and related regulatory processes. Disturbances in cellular and systemic iron balance are recognized as causes and consequences of kidney injury. Consequently, iron metabolism has become a focus for novel therapeutic interventions for acute kidney injury and chronic kidney disease, which has fuelled interest in the molecular mechanisms of renal iron handling and renal injury, as well as the complex dynamics between systemic and local cellular iron regulation.

The association between Hepcidin and arterial stiffness in a community-dwelling population

Background

An association of hepcidin with cardiovascular (CV) disease and atherosclerosis has been reported in different patient groups. However, it has not been well described clinically the association between hepcidin and arterial stiffness. In this study,We analysed the possible mechanism of Hepcidin and arterial stiffness.

Methods

This article related measurements of plasma hepcidin and arterial stiffness (carotid–femoral pulse wave velocity [PWV]) in a community-based sample.

Results

After a median follow-up interval of 4.8 years, multiple linear regression analysis revealed that hepcidin was independently associated with carotid–femoral PWV (β = 1.498, P < 0.001). In a multivariable linear regression analysis, HDL3-C levels were negatively and independently associated with hepcidin at baseline (β = − 0.857, P = 0.024). HDL2-C was not associated with hepcidin at baseline (β = − 1.121, P = 0.133).

Conclusions

We found an association between baseline hepcidin and follow-up arterial stiffness that was independent of age, gender and other vascular risk factors. We also identified an association between hepcidin and HDL3-C at baseline, which indicates that the HDL3-C level may reflect the change in cholesterol efflux from peripheral arteries and partly explain the relationship between hepcidin and the change of arterial stiffness.

Balance of cardiac and systemic hepcidin and its role in heart physiology and pathology

Hepcidin is the main regulator of iron metabolism in tissues. Its serum levels are mostly correlated with the levels of hepcidin expression from the liver, but local hepcidin can be important for the physiology of other organs as well. There is an increasing evidence that this is the case with cardiac hepcidin. This has been confirmed by studies with models of ischemic heart disease and other heart pathologies. In this review the discussion dissects the role of cardiac hepcidin in cellular homeostasis. This review is complemented with examination of the role of systemic hepcidin in heart disease and its use as a biochemical marker. The relationship between systemic vs local hepcidin in the heart is important because it can help us understand how the fine balance between the actions of two hepcidins affects heart function. Manipulating the axis systemic/cardiac hepcidin could serve as a new therapeutic strategy in heart diseases.

Relation between high serum hepcidin-25 level and subclinical atherosclerosis and cardiovascular mortality in hemodialysis patients

OBJECTIVE

In hemodialysis (HD) patients, cardiovascular disease (CVD) is the major cause of mortality and morbidity. In atherosclerotic diseases, iron gets accumulated in the arterial wall. Hepcidin is an important hormone in iron metabolism. Furthermore, hepcidin is associated with atherosclerotic disease. Therefore, this study aims to investigate the relation of serum hepcidin-25 (SH-25) and sub-clinic atherosclerosis measured by carotid intima-media thickness (CIMT) and mortality in HD patients.

METHODS

We enrolled 82 HD patients in a cross-control study. We measured SH-25 using ELISA kit and CIMT using high-resolution real-time ultrasonography. After 4 years of first assessment, we investigated the relation between all-cause and cardiovascular mortality and SH-25 and CIMT.

RESULTS

Two patients were excluded because of renal transplantation. The survivors were younger (53.7±15.1 vs. 65.2±15.5; p<0.05) and CIMT was lower (0.83±0.2 vs. 0.95±0.2; p<0.05); however, there was no significant difference in SH-25 levels between the groups (29.1±13 vs. 32.4±22.4; p=0.767). The patients who died of CVD were significantly older (63.7±16.1 vs. 53.7±15.1; p<0.05) and had significantly higher CIMT (0.94±0.2 vs. 83±0.2; p<0.05). The SH-25 levels were statistically significantly higher in patients who died of CVD (40.3±25 vs. 29.1±13; p<0.05). Linear regression analysis showed a positive correlation between CIMT and SH-25 in the study population and in those who died from CVD (r=0.41; p<0.05 and r=0.606; p<0.05, respectively).

CONCLUSION

This study suggests that hepcidin is effective in cardiovascular mortality and pathophysiology of subclinical atherosclerosis in HD patients.

Associations of plasma hepcidin with mortality risk in patients with coronary artery disease

Background

Increased blood hepcidin may be associated with the presence and promotion of atherosclerosis, the association of hepcidin with mortality among coronary artery disease (CAD) patients remains unknown. We sought to assess the relationship of hepcidin and all-cause and cardiovascular disease (CVD) mortality among CAD patients with and without acute coronary syndrome (ACS).

Methods and Results

This study included 759 patients with ACS and 526 patients with stable CAD. After an average follow-up of 4.1 years, 154 deaths were recorded, 114 were due to CVD. After adjusting for CVD risk factors and inflammatory markers, the plasma hepcidin was positively associated with all-cause and CVD mortality in the ACS patients, the multivariable-adjusted hazard ratios (HRs) across tertiles of hepcidin were 1.00, 2.18 (95% CI 1.23-3.94), and 2.82 (95% CI 1.59-5.12) for all-cause mortality (P_trend=0.006), and 1.00, 2.20 (95% CI 1.12-4.05), and 2.64 (95% CI 1.41-5.65) for CVD mortality (P_trend=0.01). The C-index and net reclassification improvement when including hepcidin in traditional CVD models were 1.6% and 21.5% for all-cause mortality, 1.4% and 23.5% for CVD mortality, respectively, (P<0.001).

Conclusions

Plasma hepcidin was positively associated with mortality in ACS patients. Hepcidin may be a potential biomarker for risk prediction in ACS patients.

The role of iron in the pathogenesis of atherosclerosis

Ferritin and increased iron stores first appeared on the list of cardiovascular risk factors more than 30 years ago and their causal role in the pathogenesis of atherosclerosis has been heavily discussed since the early 1990s. It seems that besides traditional factors such as hyperlipoproteinemia, hypertension, diabetes mellitus, obesity, physical inactivity, smoking and family history, high iron stores represent an additional parameter that could modify individual cardiovascular risk. The role of iron in the pathogenesis of atherosclerosis was originally primarily associated with its ability to catalyze the formation of highly reactive free oxygen radicals and the oxidation of atherogenic lipoproteins. Later, it became clear that the mechanism is more complex. Atherosclerosis is a chronic fibroproliferative inflammatory process and iron, through increased oxidation stress as well as directly, can control both native and adaptive immune responses. Within the arterial wall, iron affects all of the cell types that participate in the atherosclerotic process (monocytes/macrophages, endothelial cells, vascular smooth muscle cells and platelets). Most intracellular iron is bound in ferritin, whereas redox-active iron forms labile iron pool. Pro-inflammatory and anti-inflammatory macrophages within arterial plaque differ with regard to the amount of intracellular iron and most probably with regard to their labile iron pool. Yet, the relation between plasma ferritin and intracellular labile iron pool has not been fully clarified. Data from population studies document that the consumption of meat and lack of physical activity contribute to increased iron stores. Patients with hereditary hemochromatosis, despite extreme iron storage, do not show increased manifestation of atherosclerosis probably due to the low expression of hepcidin in macrophages.

Patients with acute myeloid leukemia can be subclassified based on the constitutive cytokine release of the leukemic cells; the possible clinical relevance and the importance of cellular iron metabolism

OBJECTIVE

Acute myeloid leukaemia (AML) is a heterogeneous malignancy; we studied how the constitutive cytokine release by the AML cells varies among patients.

METHODS

We investigated the constitutive release of 28 mediators during in vitro culture for 79 consecutive patients.

RESULTS

Constitutive cytokine release profiles differed among patients, and hierarchical clustering identified three subsets with high, intermediate and low release, respectively. The high-release subset showed high levels of most mediators, usually monocytic differentiation as well as altered mRNA expression of proteins involved in intracellular iron homeostasis and molecular trafficking; this subset also included 4 out of 6 patients with inv(16). Spontaneous in vitro apoptosis did not differ among the subsets. For the high-release patients, cytokines were released both by CD34⁺ and CD34^- cells. The mRNA and released protein levels showed statistically significant correlations only for eleven of the cytokines. The overall survival after intensive anti-leukemic therapy was significantly higher for high-release compared with low-release patients. Pharmacological targeting of iron metabolism (iron chelation, transferrin receptor blocking) altered the cytokine release profile.

CONCLUSIONS

Subclassification of AML patients based on the constitutive cytokine release may be clinically relevant and a part of a low-risk (i.e. chemosensitive) AML cell phenotype.

"Pumping iron"-how macrophages handle iron at the systemic, microenvironmental, and cellular levels

Macrophages reside in virtually every organ. First arising during embryogenesis, macrophages replenish themselves in the adult through a combination of self-renewal and influx of bone marrow-derived monocytes. As large phagocytic cells, macrophages participate in innate immunity while contributing to tissue-specific homeostatic functions. Among the key metabolic tasks are senescent red blood cell recycling, free heme detoxification, and provision of iron for de novo hemoglobin synthesis. While this systemic mechanism involves the shuttling of iron between spleen, liver, and bone marrow through the concerted function of defined macrophage populations, similar circuits appear to exist within the microenvironment of other organs. The high turnover of iron is the prerequisite for continuous erythropoiesis and tissue integrity but challenges macrophages’ ability to maintain cellular iron homeostasis and immune function.

This review provides a brief overview of systemic, microenvironmental, and cellular aspects of macrophage iron handling with a focus on exciting and unresolved questions in the field.

Comparison of coronary heart disease risk among four diagnostic definitions of metabolic syndrome

PURPOSE

Metabolic syndrome (MetS) is now well known as one of the major risk factors for coronary heart disease (CHD). Currently, there are several methods used to define MetS. The aim of this study was to determine to what extent current MetS definition reflects CHD risk using the probability of CHD in 10 years based on Framingham risk score algorithms.

METHODS

A total of 7575 adults, aged 16-93 years (2532 men and 5043 women), were recruited. We conducted a cross-sectional health survey in China using MetS criteria from four different definitions: modified National Cholesterol Education Program-Adult Treatment Panel III (NCEP-ATP III), International Diabetes Federation (IDF), Chinese and Japanese.

RESULTS

Differences in the prevalence of MetS by each definition were small in males (22.9-25.9 %), whereas in females, MetS was three times more prevalent using the IDF definition (29.1 %) versus the Japanese definition (9.7 %). Framingham risk scores in participants with MetS were significantly higher than in those without MetS by all definition criteria (p < 0.001). The CHD risk scores for participants with MetS by each definition showed similar values in males (range 11.5-12.1 %) with no significant differences among definitions. Conversely, in females with MetS the risk score for CHD was low (range 3.5-4.3 %) by each MetS definition.

CONCLUSIONS

These findings suggest that further studies are required to establish appropriate criteria of MetS in females.

Iron Together with Lipid Downregulates Protein Levels of Ceruloplasmin in Macrophages Associated with Rapid Foam Cell Formation

AIM

Iron accumulation in foam cells was previously shown to be involved in atherogenesis. However, the mechanism for iron accumulation was not clarified. Ceruloplasmin (Cp) is an important factor in cellular iron efflux and was found to be downregulated in atherosclerotic plaques in our previous study. The current study is to investigate the role of Cp in atherosclerosis.

METHODS

We used RAW264.7 cells, a well-accepted cell model of atherosclerosis, which were treated with lipopolysaccharides (LPS), ferric ammonium citrate (FAC) or deferoxamine, and oxidized low density lipoprotein (ox-LDL) to detect the regulation of Cp and its influence in iron efflux and lipid accumulation using biochemical and histological assays.

RESULTS

Our results showed that the Cp protein level increased after 200-μM FAC treatment in LPS-activated RAW264.7 cells. Ox-LDL treatment (50 μg/ml) moderately reduced both mRNA and protein levels and ferroxidase activity of Cp (p＜0.05). No significant difference was observed in the expression of ferritin and ferroportin, two important iron-related proteins for iron storage and efflux, respectively, after ox-LDL treatment. However, co-treatment with ox-LDL and FAC drastically reduced the expression of Cp. Accordingly, the ferroxidase activities simultaneously decreased, whereas the protein levels of Ft and Fpn1 significantly increased, indicating further iron accumulation. Moreover, co-treatment with FAC and ox-LDL enhanced the accumulation of cholesterol compared with ox-LDL-only treatment to trigger apoptosis.

CONCLUSION

Our findings suggest that physiological interaction of iron and lipid obstructs iron efflux and accelerates the lipid accumulation in macrophages during foam cell formation, which implicates the role of iron in the pathology of atherosclerosis.

Correlates of serum hepcidin levels and its association with cardiovascular disease in an elderly general population

BACKGROUND

The expression of the key iron regulatory hormone hepcidin is regulated by iron availability, inflammation, hormones, hypoxia, and anaemia. Increased serum concentrations of hepcidin have recently been linked to atherosclerosis. We studied demographic, haematologic, biochemical, and dietary correlates of serum hepcidin levels and its associations with incident cardiovascular disease and with carotid atherosclerosis.

METHODS

Serum hepcidin concentrations were measured by tandem mass spectrometry in samples taken in 2000 from 675 infection-free participants of the prospective population-based Bruneck study (age, mean±standard deviation, 66.0±10.2; 48.1% male). Blood parameters were measured by standard methods. Dietary intakes of iron and alcohol were surveyed with a food frequency questionnaire. Carotid atherosclerosis (365 cases) was assessed by ultrasound and subjects were observed for incident stroke, myocardial infarction, or sudden cardiac death (91 events) until 2010.

RESULTS

Median (interquartile range) hepcidin levels were 2.27 nM (0.86, 4.15). Most hepcidin correlates were in line with hepcidin as an indicator of iron stores. Independently of ferritin, hepcidin was related directly to physical activity (p=0.024) and fibrinogen (p<0.0001), and inversely to alcohol intake (p=0.006), haemoglobin (p=0.027), and γ-glutamyltransferase (p<0.0001). Hepcidin and hepcidin-to-ferritin ratio were not associated with prevalent carotid atherosclerosis (p=0.43 and p=0.79) or with incident cardiovascular disease (p=0.62 and p=0.33).

CONCLUSIONS

In this random sample of the general community, fibrinogen and γ-glutamyltransferase were the most significant hepcidin correlates independent of iron stores, and hepcidin was related to neither atherosclerosis nor cardiovascular disease.

Monocyte Chemoattractant Protein-1 and Large Artery Structure and Function in Young Individuals: The African-PREDICT Study

To better understand hypertension development, the authors determined whether monocyte chemoattractant protein-1 (MCP-1) is associated with arterial stiffness (pulse wave velocity [PWV]) and carotid intima-media wall thickness (cIMT) in a young apparently healthy black and white population (N=403, aged 20-30 years). Carotid-femoral PWV, central systolic blood pressure, and cIMT were measured, and MCP-1, reactive oxygen species, inflammatory markers (interleukin 6, tumor necrosis factor α), and endothelial activation (intercellular adhesion molecule, vascular cell adhesion molecule) were determined from blood samples. Although carotid-femoral PWV and cIMT were similar between blacks and whites, black men and women showed higher central systolic blood pressure, MCP-1, and reactive oxygen species than whites (all P<.05). In addition, black women had higher brachial blood pressure and interleukin 6 (all P<.001). A consistent positive association only in black women between cIMT and MCP-1 in multiple regression analyses was found (R²=0.151, β=0.248; P=.021). In this model, cIMT was also independently associated with vascular cell adhesion molecule (β=0.251; P=.022). The authors found elevated central systolic blood pressure and MCP-1 in young blacks, where cIMT was independently associated with MCP-1 in black women.

Intravenous Iron Carboxymaltose as a Potential Therapeutic in Anemia of Inflammation

Intravenous iron supplementation is an effective therapy in iron deficiency anemia (IDA), but controversial in anemia of inflammation (AI). Unbound iron can be used by bacteria and viruses for their replication and enhance the inflammatory response. Nowadays available high molecular weight iron complexes for intravenous iron substitution, such as ferric carboxymaltose, might be useful in AI, as these pharmaceuticals deliver low doses of free iron over a prolonged period of time. We tested the effects of intravenous iron carboxymaltose in murine AI: Wild-type mice were exposed to the heat-killed Brucella abortus (BA) model and treated with or without high molecular weight intravenous iron. 4h after BA injection followed by 2h after intravenous iron treatment, inflammatory cytokines were upregulated by BA, but not enhanced by iron treatment. In long term experiments, mice were fed a regular or an iron deficient diet and then treated with intravenous iron or saline 14 days after BA injection. Iron treatment in mice with BA-induced AI was effective 24h after iron administration. In contrast, mice with IDA (on iron deficiency diet) prior to BA-IA required 7d to recover from AI. In these experiments, inflammatory markers were not further induced in iron-treated compared to vehicle-treated BA-injected mice. These results demonstrate that intravenous iron supplementation effectively treated the murine BA-induced AI without further enhancement of the inflammatory response. Studies in humans have to reveal treatment options for AI in patients.

Hepcidin and iron metabolism associated with cardiometabolic risk factors in children: A case-control study

BACKGROUND AND AIMS

Iron metabolism plays a crucial role in the development of cardiometabolic disease; however, the association between cardiometabolic risk factors (CMRFs) and hepcidin as well as other iron parameters remains unclear in children. The aims of this study were to compare the circulating hepcidin levels and iron metabolism between children with and without CMRFs and to investigate the association between those iron parameters and CMRFs.

METHODS AND RESULTS

A case-control study was conducted among 1126 children aged 7-14 years in the case group (n = 563) with CMRFs and the healthy control group (n = 563). Iron parameters, lipids, and anthropometric characteristics were evaluated. The information on demographics, diet, and physical activities was either children reported or parent reported. Compared with the healthy controls, children with CMRFs had higher levels of hepcidin and lower levels of serum iron, transferrin, and soluble transferrin receptor (sTfR; P < 0.001). Besides, the odds ratios (ORs) for low levels of high-density lipoprotein (HDL) were 2.03, 0.21, and 0.33 in children with higher hepcidin, transferrin, and sTfR levels (P < 0.05). Furthermore, ORs for cardiometabolic risk were 0.50 (95% confidence interval (CI): 0.30-0.85, P < 0.05), 0.22 (95% CI: 0.12, 0.42, P < 0.01) and 0.19 (95% CI: 0.10, 0.36, P < 0.01) in children with higher serum iron, transferrin, and sTfR levels, respectively.

CONCLUSION

The levels of hepcidin were higher, while those of iron, transferrin, and sTfR were lower in children with CMRF. Hepcidin was positively associated with the risk of low HDL levels, whereas transferrin and sTfR levels negatively correlated with the risk of low HDL levels. In addition, serum iron, transferrin, and sTfR levels were negatively associated with cardiometabolic risk.

Vascular Damage in Patients with Nonalcoholic Fatty Liver Disease: Possible Role of Iron and Ferritin

Non Alcoholic Fatty Liver Disease (NAFLD) is the most common chronic liver disease in Western countries. Recent data indicated that NAFLD is a risk factor by itself contributing to the development of cardiovascular disease independently of classical known risk factors. Hyperferritinemia and mild increased iron stores are frequently observed in patients with NAFLD and several mechanisms have been proposed to explain the role of iron, through oxidative stress and interaction with insulin metabolism, in the development of vascular damage. Moreover, iron depletion has been shown to decrease atherogenesis in experimental models and in humans. This review presents the recent evidence on epidemiology, pathogenesis, and the possible explanation of the role of iron and ferritin in the development of cardiovascular damage in patients with NAFLD, and discusses the possible interplay between metabolic disorders associated with NAFLD and iron in the development of cardiovascular disease.

Iron gene expression profile in atherogenic Mox macrophages

RATIONALE

The role of macrophage iron in the physiopathology of atherosclerosis is an open question that needs to be clarified. In atherosclerotic lesions, recruited macrophages are submitted to cytokines and oxidized lipids which influence their phenotype. An important phenotypic population driven by oxidized phospholipids is the Mox macrophages which present unique biological properties but their iron phenotype is not well described.

OBJECTIVE

To investigate the effect of Mox polarization by oxidized LDL (oxLDL) on macrophage iron metabolism in the absence or presence of proinflammatory stimuli.

METHODS

Bone marrow-derived macrophages were treated with different sources of LDL and/or LPS/IFNγ (M1 activator). Expression of ferroportin (Slc40a1, alias Fpn), heme oxygenase-1 (Hmox1), H- and L-ferritin (Fth1 and Ftl1), hepcidin (Hamp), ceruloplasmin (Cp) and interleukine-6 (Il6) was followed by quantitative PCR. FPN and HMOX1 protein expression was analyzed by immunofluorescence and in-cell-Western blotting.

RESULTS

Mox macrophages expressed increased Hmox1 and Fth1 levels with basal FPN protein levels despite the significant increase of Fpn mRNA. Upregulation of Hmox1 and Fpn mRNA was specific to LDL oxidative modification and mediated by NRF2. The downregulation of both Cp isoforms and the upregulation of Hamp expression observed in Mox macrophages suggest that FPN mediated iron export could be compromised. Simultaneous exposure to oxLDL and LPS/IFNγ leads to a mixed Mox/M1 phenotype that is closer to M1.

CONCLUSION

A microenvironment rich in oxLDL and proinflammatory cytokines could promote macrophage iron retention and lipid accumulation profiles, a specific cell phenotype that likely contributes to lesion development and plaque instability in atherosclerosis.

Serum Ferritin Relates to Carotid Intima-Media Thickness in Offspring of Fathers With Higher Serum Ferritin Levels

OBJECTIVE

Body iron status has been linked to atherosclerosis in adults. The purposes of our study were to determine (1) the association between circulating ferritin levels and carotid intima-media thickness (cIMT) in a cohort of apparently healthy children and (2) the association between cIMT and parental ferritin levels.

APPROACH AND RESULTS

Circulating ferritin levels (microparticle enzyme immunoassay), metabolic parameters, and cIMT (ultrasonography) were analyzed cross-sectionally in a cohort of 692 healthy white children with a mean age of 8 ± 2 years (52% girls and 48% boys). In consecutive 123 children from the cross-sectional sample, the same serum assessments were also performed at baseline in their parents, and the cIMT was repeated after 3 years of follow-up in the children at a mean age of 11 ± 2 years (53% girls and 47% boys). Weak but significant positive associations were evident between children's circulating ferritin levels and cIMT (r=0.123; P=0.001) and with the change in cIMT 3 years later a tendency was also observed (r=0.185; P=0.048). In multiple regression analyses, circulating ferritin levels contributed independently to cIMT variance (β=0.090; P=0.026; R(2)=10%) and cIMT change variance (β=0.216; P=0.019; R(2)= 3.4%) after controlling for body mass index, high-sensitivity C-reactive protein, age, sex, and low-density lipoprotein-cholesterol levels. This association was, however, remarkably significant (β=0.509; P=0.001; R(2)= 20.4%) in children whose fathers had ferritin levels above the median value (122.5 ng/mL).The latter association remained significant after correction for multiple testing. Maternal's ferritin levels showed no interaction in this association.

CONCLUSIONS

These results suggest a paternal-specific effect on cIMT partially reflected by father's ferritin levels.

4'-O-β-D-glucosyl-5-O-methylvisamminol, an active ingredient of Saposhnikovia divaricata, attenuates high-mobility group box 1 and subarachnoid hemorrhage-induced vasospasm in a rat model

Background

High-mobility group box 1 (HMGB1) was observed to be an important extracellular mediator involved in vascular inflammation associated with subarachnoid hemorrhage (SAH). This study is of interest to examine the efficacy of 4′-O-β-d-glucosyl-5-O-methylvisamminol (4OGOMV), C₂₂H₂₈O₁₀, on the alternation of cytokines and HMGB1 in an animal model.

Methods

A rodent double hemorrhage SAH model was employed. Administration with 4OGOMV was initiated 1 h after animals were subjected to SAH. Basilar arteries (BAs) were harvested and cortexes examined for HMGB1 mRNA, protein expression (Western blot) and monocyte chemoattractant protein-1 (MCP-1) immunostaining. Cerebrospinal fluid samples were collected to examine IL-1β, IL-6, IL-8 and MCP-1 (rt-PCR).

Results

Morphological findings revealed endothelial cell deformity, intravascular elastic lamina torture, and smooth muscle necrosis in the vessels of SAH groups. Correspondently, IL-1β, IL-6 and MCP-1 in the SAH-only and SAH-plus vehicle groups was also elevated. 4OGOMV dose-dependently reduced HMGB1 protein expression when compared with the SAH groups.(p < 0.01) Likewise, 400 μg/kg 4OGOMV reduced IL-1β, MCP-1 and HMGB1 mRNA levels as well as MCP-1(+) monocytes when compared with the SAH groups..

Conclusion

4OGOMV exerts its neuro-protective effect partly through the dual effect of inhibiting IL-6 and MCP-1 activation and also reduced HMGB1 protein, mRNA and MCP-1(+) leukocytes translocation. This study lends credence to validating 4OGOMV as able to attenuate pro-inflammatory cytokine mRNA, late-onset inflammasome, and cellular basis in SAH-induced vasospasm.

Is hepcidin-25 a predictor of atherosclerosis in hemodialysis patients?

Atherosclerotic cardiovascular disease is an important cause of mortality and morbidity in hemodialysis patients. Iron accumulation in arterial wall macrophages is increased in atherosclerotic lesions. Hepcidin is a key hepatic hormone regulating iron balance. It inhibits iron release from macrophages and iron absorption from enterocytes by binding and inactivating the cellular iron exporter ferroportin. The aim of this study is to investigate the relation of hepcidin-25, iron parameters, and atherosclerosis measured by carotid intima media thickness (CIMT) in hemodialysis patients. Eighty-two hemodialysis patients were enrolled in this cross-sectional study. Predialysis blood samples were centrifuged at 1500 g and 4°C for 10 minutes and stored at -80°C for the measurement of hepcidin-25. DRG hepcidin enzyme-linked immunosorbent assay kit was used for the measurement of hepcidin-25. Ultrasonographical B-mode imaging of bilateral carotid arteries was performed with a high-resolution real-time ultrasonography (Mindray DC7). Mean age of the study population was 57.90 ± 16.08 years and 43.9% were men. Total study population was grouped into two according to median value of hepcidin-25. There was no difference between groups with respect to age, dialysis vintage, and C-reactive protein. CIMT was found to be statistically significantly higher in low hepcidin-25 group. In correlation analysis, CIMT was found to be correlated with age (P < 0.01, R = 0.33) and hepcidin-25 (P < 0.01, R = 0.46). In linear regression analysis, age (β = 0.31) and hepcidin-25 (β = 0.44) were found to be the determinants of CIMT in hemodialysis patients. Our results implicate that hepcidin may take part in pathophysiology of atherosclerosis and cardiovascular disease in hemodialysis patients.

Iron Stores, Hepcidin, and Aortic Stiffness in Individuals with Hypertension

Background & Aims

Iron accumulation within the arterial wall has been hypothesized to promote atherosclerosis progression. Aim of this study was to evaluate whether the hormone hepcidin and iron stores are associated with arterial stiffness in subjects with essential hypertension.

Methods

Circulating hepcidin, ferritin, and mutations in the hemochromatosis gene were compared between subjects included in the first vs. third tertile (n=284 each) of carotid-femoral pulse wave velocity (PWV) in an unselected cohort of patients with arterial hypertension.

Results

At univariate logistic regression analysis, high PWV was associated with higher ferritin levels (p=0.010), but lower hepcidin (p=0.045), and hepcidin ferritin/ratio (p<0.001). Hemochromatosis mutations predisposing to iron overload were associated with high PWV (p=0.025). At multivariate logistic regression analysis, high aortic stiffness was associated with older age, male sex, lower BMI, higher systolic blood pressure and heart rate, hyperferritinemia (OR 2.05, 95% c.i. 1.11-3.17 per log ng/ml; p=0.022), and lower circulating hepcidin concentration (OR 0.29, 95% c.i. 0.16-0.51 per log ng/ml; p<0.001). In subgroup analyses, high PWV was associated with indices of target organ damage, including micro-albuminuria (n=125, p=0.038), lower ejection fraction (n=175, p=0.031), cardiac diastolic dysfunction (p=0.004), and lower S wave peak systolic velocity (p<0.001). Ferritin was associated with cardiac diastolic dysfunction, independently of confounders (p=0.006).

Conclusions

In conclusion, hyperferritinemia is associated with high aortic stiffness and cardiac diastolic dysfunction, while low circulating hepcidin with high aortic stiffness.

Deferoxamine but not dexrazoxane alleviates liver injury induced by endotoxemia in rats

The purpose of the present study was to compare the activity of two different clinically available iron chelators on the development of acute liver injury after administration of the bacterial endotoxin (lipopolysaccharide [LPS]) in rats. Lipopolysaccharide was administered either alone or after pretreatment with dexrazoxane (DEX) or deferoxamine (DFO). Control groups received only saline or its combination with either chelator. After 8 h, untreated LPS rats developed liver injury, with signs of inflammation and oxidative stress. Lipopolysaccharide reduced plasma iron concentrations in association with increased production of hepcidin and the reduced liver expression of ferroportin. Administration of chelating agents to LPS animals showed distinct effects. Although both drugs were able to reduce liver iron content, together with corresponding changes in hepcidin and ferroportin expressions, only DFO showed a protective effect against liver injury despite relatively small liver concentrations. In sharp contrast, DEX failed to improve any hallmark of liver injury and even worsened the GSH/GSSG ratio, the indicator of oxidative stress in the tissue. High-performance liquid chromatography-mass spectrometry analysis showed marked liver accumulation of iron-chelating metabolite of DEX (ADR-925), whereas the parent compound was undetectable. Further downregulation of transporters involved in bile formation was observed after DFO in the LPS group as well as in healthy animals. Neither chelator imposed significant liver injury in healthy animals. In conclusion, we demonstrated marked differences in the modulation of endotoxemic liver impairment between two iron chelators, implicating that particular qualities of chelating agents may be of crucial importance.

Iron and noncontrast magnetic resonance T2* as a marker of intraplaque iron in human atherosclerosis

OBJECTIVE

Iron has been implicated in atherogenesis and plaque destabilization, whereas less is known about iron-related proteins in this disease. We compared ex vivo quantities with in vivo vessel wall T2*, which is a noncontrast magnetic resonance relaxation time that quantitatively shortens with increased tissue iron content. We also tested the hypothesis that patients with carotid atherosclerosis have abnormal T2* times vs controls that would help support a role for iron in human atherosclerosis.

METHODS

Forty-six patients undergoing carotid endarterectomy and 14 subjects without carotid disease were prospectively enrolled to undergo carotid magnetic resonance imaging. Ex vivo measurements were performed on explanted plaque and 17 mammary artery samples.

RESULTS

Plaques vs normal arteries had higher levels of ferritin (median, 7.3 [interquartile range (IQR), 4-13.8] vs 1.0 [IQR, 0.6-1.3] ng/mg; P < .001) and oxidized low-density lipoprotein (median, 0.17 [IQR, 0.12-0.30] vs 0.01 [IQR, 0.003-0.03] ng/mg; P < .001) as well as hepcidin (median, 8.7 [IQR, 4.6-12.4] vs 2.6 [IQR, 1.3-7.0] ng/mL; P = .03); serum hepcidin levels did not distinguish atherosclerosis patients from controls (median, 40.6 [IQR, 18.8-88.6] vs 33.9 [IQR, 17.6-55.2]; P = .42). Shorter in vivo T2* paralleled larger plaque volume (ρ = -.44; P = .01), and diseased arteries had shorter T2* values compared with controls (median, 17.7 ± 4.3 vs 23.0 ± 2.4 ms; P < .001).

CONCLUSIONS

Diseased arteries have greater levels of iron-related proteins ex vivo and shorter T2* times in vivo. Further studies should help define the role of T2* as a biomarker of iron and atherosclerosis.

Serum hepcidin predicts uremic accelerated atherosclerosis in chronic hemodialysis patients with diabetic nephropathy

BACKGROUND

Hepcidin, as a regulator of body iron stores, has been recently discovered to play a critical role in the pathogenesis of anemia of chronic disease. Atherosclerotic cardiovascular disease is the most common complication and the leading cause of death in chronic hemodialysis (CHD) patients. In the current study, we aimed to explore the relationship between serum hepcidin and uremic accelerated atherosclerosis (UAAS) in CHD patients with diabetic nephropathy (CHD/DN).

METHODS

A total of 78 CHD/DN and 86 chronic hemodialyzed nondiabetic patients with chronic glomerulonephritis (CHD/non-DN) were recruited in this study. The level of serum hepcidin-25 was specifically measured by liquid chromatography-tandem mass spectrometry. Serum levels of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were measured by enzyme-linked immunosorbent assay.

RESULTS

High serum level of hepcidin-25 was seen in CHD patients. Serum hepcidin-25 in CHD/DN was significantly higher than that in CHD/non-DN patients. Serum hepcidin-25 was positively correlated with ferritin, high-sensitivity C-reactive protein (hs-CRP), TNF-α, and IL-6 in CHD/DN patients. CHD/DN patients exhibited higher common carotid artery intima media thickness (CCA-IMT), hs-CRP, and hepcidin-25 levels than that in CHD/non-DN patients. Moreover, in CHD/DN patients, CCA-IMT was positively correlated with serum hepcidin, hs-CRP, and low-density lipoprotein-cholesterol. On multiple regression analysis, serum hepcidin and hs-CRP level exhibited independent association with IMT in CHD/DN patients.

CONCLUSIONS

These findings suggest possible linkage between iron metabolism and hepcidin modulation abnormalities that may contribute to the development of UAAS in CHD/DN patients.

Particulate matter phagocytosis induces tissue factor in differentiating macrophages

Airborne exposure to particulate matter with diameter < 10 mcM (PM10) has been linked to an increased risk of thromboembolic events, but the mechanisms are not completely understood. The aim of this study was to evaluate the effect of PM10 phagocytosis on the release of procoagulant molecules in human differentiating macrophages, and that of PM10 inhalation in an experimental model in rats. Human monocytes were separated from the peripheral blood by the lymphoprep method, differentiated in vitro and treated with standard PM10 or vehicle. Sprague-Dawley rats were instilled intratracheally with PM10 or vehicle alone. The outcome was expression of proinflammatory genes and of tissue factor (TF). In human differentiating macrophages, PM10 exposure upregulated inflammatory genes, but most consistently induced TF mRNA and protein levels, but not TF protein inhibitor, resulting in increased TF membrane expression and a procoagulant phenotype. Differentiation towards the anti-inflammatory M2 phenotype inhibited PM10 -mediated TF expression. TF induction required phagocytosis of PM10 , whereas phagocytosis of inert particles was less effective. PM10 phagocytosis was associated with a gene expression profile consistent with intracellular retention of iron, inducing oxidative stress. Both PM10 and iron activated the stress kinases ERK1/2 pathway, involved in the induction of TF expression. In rats, alveolar exposure to PM10 was associated with pulmonary recruitment of inflammatory cells and resulted in local, but not systemic, induction of TF expression, which was sufficient to increase circulating TF levels. In conclusion, TF induction by differentiating lung macrophages, activated following phagocytosis, contributes to the increased risk of thromboembolic complications associated with PM10 exposure.

Mutual interaction between iron homeostasis and obesity pathogenesis

Obesity is identified as an important medical problem. One of the pathologic conditions observed in obesity is systemic iron deficiency and hypoferremia. Along with a large number of studies indicating disturbed iron homeostasis in obesity, recent data indicate a cause-effect relationship between iron status and obesity-related pathologies. The primary objective of the article is to consider two aspects of the iron-obesity interplay: (1) the mechanisms leading to impaired iron balance, and (2) the pathways of iron participation in obesity-related pathogenesis. While considering disturbance of iron homeostasis in obesity, a number of potential mechanisms of hypoferremia are proposed. At the same time, the inflammation of obesity and obesity-related hepcidin and lipocalin 2 hyperproduction seem to be the most probable reasons of obesity-related hypoferremia. Oversecretion of these proteins leads to iron sequestration in reticuloendothelial system cells. The latter also leads to increased adipose tissue iron content, thus producing preconditions for adverse effects of local iron overload. Being a redox-active metal, iron is capable of inducing oxidative stress as well as endoplasmic reticulum stress, inflammation and adipose tissue endocrine dysfunction. Iron-mediated mechanisms of toxicity may influence aspects of obesity pathogenesis possibly even leading to obesity aggravation. Thus, a mutual interaction between disturbance in iron homeostasis and obesity pathogenesis is proposed. All sides of this interaction should be considered to design new therapeutic approaches to the treatment of disturbed iron homeostasis in obesity.

Macrophages: central regulators of iron balance

Macrophages are important to immune function and also actively participate in iron homeostasis. The involvement of splenic and liver macrophages in the processing of effete erythrocytes and the subsequent return of iron to the circulation is well established, and the molecular details of iron recycling have been characterized recently. Another important aspect regarding iron handling by macrophages is their capacity to act as immune cells, which involves the inflammatory response, as well as other pathological conditions in which macrophages are central. This review discusses the latest advances in macrophage iron trafficking and the pathophysiological consequences of altered iron homeostasis in these cells.

Chelation of dietary iron prevents iron accumulation and macrophage infiltration in the type I diabetic kidney

We previously reported that the functional deletion of p21, a cyclin-dependent kinase inhibitor, in mice attenuated renal cell senescence in streptozotocin (STZ)-induced type 1 diabetic mice. In the present study, we investigated the effect of iron chelation on renal cell senescence and inflammation in the type 1 diabetic kidney. STZ-treated mice showed increase in iron accumulation, tubular cell senescence and macrophage infiltration at week 28 in the kidney. Administering deferasirox, which removes only dietary iron, significantly attenuated iron accumulation in proximal tubules and the number of infiltrating F4/80-positive cells without effecting blood glucose, hematocrit or hemoglobin levels. In contrast however, deferasirox did not influence renal cell senescence. The lack of p21 decreased the renal tubular iron accumulation and did not change tubular cell senescence. Interestingly, the STZ-treated animals showed an increase in p16, another cyclin-dependent kinase inhibitor. The results suggest that type 1 diabetes increases renal tubular iron accumulation and macrophage infiltration through a p21-dependent mechanism, and that the chelation of dietary iron attenuates these responses.

The interplay among iron metabolism, endothelium and inflammatory cascade in dysmetabolic disorders

PURPOSE

Metabolic syndrome (MetS) is considered as a proinflammatory and prothrombotic state with atherogenic risk factors including dyslipidemia, obesity and glucose intolerance. Oxidative stress is a unifying basis of several disorders including diabetes mellitus (DM) and MetS. We therefore designed this cross-sectional study to investigate the potential interaction among iron metabolism, inflammation and endothelial plexus in MetS and DM patients.

METHODS

A total of 62 patients [median age 54 (23-76) years; male/female 16/46] and 18 healthy controls [median age 38 (30-64) years; male/female 6/12] were included in the study. Patient population was classified as MetS (n = 30) and DM (n = 32).

RESULTS

Leukocyte count (p = 0.002) and osteopontin (OPN) levels (p = 0.008) were significantly higher, while C-reactive protein (CRP) (p = 0.056) and IL-6 (p = 0.059) represented a relative increase in the patient group. Leptin, endothelin 1 (ET1), hepcidin, nitric oxide synthase (NOS), erythrocyte sedimentation rate (ESR), iron, transferrin saturation (TS) and ferritin levels were not significantly different between the patient and control groups. Endothelin 1 was found to be higher in the DM group compared to MetS group (p = 0.15, p = 0.049). Leukocyte count, leptin, hepcidin, OPN, NOS, IL-6, ESR, CRP, iron, TS and ferritin levels were not different between DM and MetS groups. A positive correlation was demonstrated between leptin and OPN (p = 0.001, r = 0.360), ferritin and hepcidin (p < 0.01, r = 0.633), IL-6 and CRP (p = 0.023, r = 0.319), leptin and NOS (p = 0.005, r = 0.309) and OPN and NOS (p < 0.001, r = 0.803). There was a negative correlation between hepcidin and NOS (p = 0.009, r = -0.289). When the study cohort was divided into two particular groups based on median ferritin and hepcidin levels, hepcidin (p = 0.002), ALT (p = 0.001) and LDL (p = 0.049) levels were higher in the high-ferritin group. Nitric oxide synthase levels (p = 0.033) were lower, whereas ferritin levels (p = 0.004) were higher in the high-hepcidin group.

CONCLUSION

Mechanisms involved in the vicious circle of MetS including inflammation, endothelial vasculature and iron metabolism remain to be elucidated. The role of iron metabolism in this complex interaction should be confirmed with further studies.

High fat diet subverts hepatocellular iron uptake determining dysmetabolic iron overload

Increased serum ferritin associated with mild hepatic iron accumulation, despite preserved upregulation of the iron hormone hepcidin, is frequently observed in patients with dysmetabolic overload syndrome (DIOS). Genetic factors and Western diet represent predisposing conditions, but the mechanisms favoring iron accumulation in DIOS are still unclear. Aims of this study were to assess the effect a high-fat diet (HFD) on hepatic iron metabolism in an experimental model in rats, to further characterize the effect of free fatty acids on iron metabolism in HepG2 hepatocytes in vitro, and to assess the translational relevance in patients with fatty liver with and without iron accumulation. Despite decreased uptake of dietary iron, rats fed HFD accumulated more hepatic iron than those fed regular diet, which was associated with steatosis development. Hepatic iron accumulation was paralleled by induction of ferritin, in the presence of preserved upregulation of hepcidin, recapitulating the features of DIOS. HFD was associated with increased expression of the major iron uptake protein Transferrin receptor-1 (TfR-1), consistently with upregulation of the intracellular iron sensor Iron regulated protein-1 (IRP1). Supplementation with fatty acids induced TfR-1 and IRP1 in HepG2 hepatocytes, favoring intracellular iron accumulation following exposure to iron salts. IRP1 silencing completely abrogated TfR-1 induction and the facilitation of intracellular iron accumulation induced by fatty acids. Hepatic TfR-1 mRNA levels were upregulated in patients with fatty liver and DIOS, whereas they were not associated with liver fat nor with inflammation. In conclusion, increased exposure to fatty acids subverts hepatic iron metabolism, favoring the induction of an iron uptake program despite hepatocellular iron accumulation.

Hepcidin levels in chronic hemodialysis patients: a critical evaluation

Altered systemic iron metabolism is a key element of uremia, and functional iron deficiency mainly related to subclinical inflammation makes it difficult to maintain proper control of anemia in chronic hemodialysis patients (CHD). In the last decade, the hepatic hormone hepcidin has been progressively recognized as the master regulator of circulating iron levels through the modulation of cellular iron fluxes in response to iron stores, as well as to erythroid and inflammatory stimuli. Hepcidin is cleared by the kidney and progression of renal disease has been associated to increased serum hepcidin levels. This, in turn, reduces iron availability for erythropoiesis, suggesting anti-hepcidin strategies for improving anemia control. Moreover, hepcidin has been recently implicated in the pathogenesis of long-term complications of dialysis, like accelerated atherosclerosis. Initial studies almost invariably reported a sustained increase of serum hepcidin in chronic hemodialysis patients. Noteworthy, such studies included relatively few patients and controls that were poorly matched for major determinants of serum hepcidin at population level, i.e., age and gender. More recent data based on accurately matched larger series challenge the view that hepcidin is intrinsically increased in hemodialysis patients, showing a marked inter- and intra-individual variability of hormone levels. Here we take a critical look to the data published so far on hepcidin levels in CHD, analyze the reasons underlying the discrepancies in available studies and the hepcidin variability in CHD, and point out the need for further studies in large series of well-characterized CHD patients and controls.

Serum ferritin is an important inflammatory disease marker, as it is mainly a leakage product from damaged cells

"Serum ferritin" presents a paradox, as the iron storage protein ferritin is not synthesised in serum yet is to be found there. Serum ferritin is also a well known inflammatory marker, but it is unclear whether serum ferritin reflects or causes inflammation, or whether it is involved in an inflammatory cycle. We argue here that serum ferritin arises from damaged cells, and is thus a marker of cellular damage. The protein in serum ferritin is considered benign, but it has lost (i.e. dumped) most of its normal complement of iron which when unliganded is highly toxic. The facts that serum ferritin levels can correlate with both disease and with body iron stores are thus expected on simple chemical kinetic grounds. Serum ferritin levels also correlate with other phenotypic readouts such as erythrocyte morphology. Overall, this systems approach serves to explain a number of apparent paradoxes of serum ferritin, including (i) why it correlates with biomarkers of cell damage, (ii) why it correlates with biomarkers of hydroxyl radical formation (and oxidative stress) and (iii) therefore why it correlates with the presence and/or severity of numerous diseases. This leads to suggestions for how one might exploit the corollaries of the recognition that serum ferritin levels mainly represent a consequence of cell stress and damage.

Effects of iron overload on chronic metabolic diseases

Iron can affect the clinical course of several chronic metabolic diseases such as type 2 diabetes, obesity, non-alcoholic fatty liver disease, and atherosclerosis. Iron overload can affect major tissues involved in glucose and lipid metabolism (pancreatic β cells, liver, muscle, and adipose tissue) and organs affected by chronic diabetic complications. Because iron is a potent pro-oxidant, fine-tuned control mechanisms have evolved to regulate entry, recycling, and loss of body iron. These mechanisms include the interplay of iron with transferrin, ferritin, insulin, and hepcidin, as well as with adipokines and proinflammatory molecules. An imbalance of these homoeostatic mechanisms results in systemic and parenchymal siderosis that contributes to organ damage (such as β-cell dysfunction, fibrosis in liver diseases, and atherosclerotic plaque growth and instability). Conversely, iron depletion can exert beneficial effects in patients with iron overload and even in healthy frequent blood donors. Regular assessment of iron balance should be recommended for patients with chronic metabolic diseases, and further research is needed to produce guidelines for the identification of patients who would benefit from iron depletion.

Atherogenesis and iron: from epidemiology to cellular level

Iron accumulates in human atherosclerotic lesions but whether it is a cause or simply a downstream consequence of the atheroma formation has been an open question for decades. According to the so called "iron hypothesis," iron is believed to be detrimental for the cardiovascular system, thus promoting atherosclerosis development and progression. Iron, in its catalytically active form, can participate in the generation of reactive oxygen species and induce lipid-peroxidation, triggering endothelial activation, smooth muscle cell proliferation and macrophage activation; all of these processes are considered to be proatherogenic. On the other hand, the observation that hemochromatotic patients, affected by life-long iron overload, do not show any increased incidence of atherosclerosis is perceived as the most convincing evidence against the "iron hypothesis." Epidemiological studies and data from animal models provided conflicting evidences about the role of iron in atherogenesis. Therefore, more careful studies are needed in which issues like the source and the compartmentalization of iron will be addressed. This review article summarizes what we have learnt about iron and atherosclerosis from epidemiological studies, animal models and cellular systems and highlights the rather contributory than innocent role of iron in atherogenesis.

The role of vitamin D in regulating the iron-hepcidin-ferroportin axis in monocytes

Chronic kidney disease affects 40% of adults aged 65 and older. Anemia of CKD is present in 30% of patients with CKD and is associated with increased cardiovascular risk, decreased quality of life, and increased mortality. Hepcidin-25 (hepcidin), the key iron regulating hormone, prevents iron egress from macrophages and thus prevents normal recycling of the iron needed to support erythropoiesis. Hepcidin levels are increased in adults and children with CKD. Vitamin D insufficiency is highly prevalent in CKD and is associated with erythropoietin hyporesponsiveness. Recently, hepcidin levels were found to be inversely correlated with vitamin D status in CKD. The aim of this study was to investigate the role of vitamin D in the regulation of hepcidin expression in vitro and in vivo. This study reports that 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), the hormonally active form of vitamin D, is associated with decreased hepcidin and increased ferroportin expression in lipopolysaccharide (LPS) stimulated THP-1 cells. 1,25(OH)₂D₃ also resulted in a dose-dependent decrease in pro-hepcidin cytokines, IL-6 and IL-1β, release in vitro. Further, we show that high-dose vitamin D therapy impacts systemic hepcidin levels in subjects with early stage CKD. These data suggest that improvement in vitamin D status is associated with lower systemic concentrations of hepcidin in subjects with CKD. In conclusion, vitamin D regulates the hepcidin-ferroportin axis in macrophages which may facilitate iron egress. Improvement in vitamin D status in patients with CKD may reduce systemic hepcidin levels and may ameliorate anemia of CKD.

Out of balance--systemic iron homeostasis in iron-related disorders

Iron is an essential element in our daily diet. Most iron is required for the de novo synthesis of red blood cells, where it plays a critical role in oxygen binding to hemoglobin. Thus, iron deficiency causes anemia, a major public health burden worldwide. On the other extreme, iron accumulation in critical organs such as liver, heart, and pancreas causes organ dysfunction due to the generation of oxidative stress. Therefore, systemic iron levels must be tightly balanced. Here we focus on the regulatory role of the hepcidin/ferroportin circuitry as the major regulator of systemic iron homeostasis. We discuss how regulatory cues (e.g., iron, inflammation, or hypoxia) affect the hepcidin response and how impairment of the hepcidin/ferroportin regulatory system causes disorders of iron metabolism.