Serum Iron Availability Research Articles

Impaired iron recycling from erythrocytes is an early hallmark of aging.

Aging affects iron homeostasis, as evidenced by tissue iron loading and anemia in the elderly. Iron needs in mammals are met primarily by iron recycling from senescent red blood cells (RBCs), a task chiefly accomplished by splenic red pulp macrophages (RPMs) via erythrophagocytosis. Given that RPMs continuously process iron, their cellular functions might be susceptible to age-dependent decline, a possibility that has been unexplored to date. Here, we found that 10- to 11-month-old female mice exhibit iron loading in RPMs, largely attributable to a drop in iron exporter ferroportin, which diminishes their erythrophagocytosis capacity and lysosomal activity. Furthermore, we identified a loss of RPMs during aging, underlain by the combination of proteotoxic stress and iron-dependent cell death resembling ferroptosis. These impairments lead to the retention of senescent hemolytic RBCs in the spleen, and the formation of undegradable iron- and heme-rich extracellular protein aggregates, likely derived from ferroptotic RPMs. We further found that feeding mice an iron-reduced diet alleviates iron accumulation in RPMs, enhances their ability to clear erythrocytes, and reduces damage. Consequently, this diet ameliorates hemolysis of splenic RBCs and reduces the burden of protein aggregates, mildly increasing serum iron availability in aging mice. Taken together, we identified RPM collapse as an early hallmark of aging and demonstrated that dietary iron reduction improves iron turnover efficacy.

Iron metabolism regulation in females and males exposed to simulated microgravity: results from the randomized trial Artificial Gravity Bed Rest—European Space Agency (AGBRESA)

Iron metabolism imbalance could contribute to physical deconditioning experienced by astronauts due to its essential role in energy metabolism, cellular respiration, and oxygen transport. In this clinical exploratory study, we wanted to determine whether artificial gravity (AG) training modulated iron metabolism, RBC indices, and body lean mass in healthy male and female participants exposed to head-down tilt (HDT) bed rest, the reference ground-based model of microgravity. We recruited 8 healthy female and 16 healthy male participants who were all exposed to HDT bed rest for 60 d. In addition, they were assigned to 3 experimental groups (n = 8/each): controls, continuous AG training in a short-arm centrifuge (1 × 30 min/d), and intermittent AG training (6 × 5 min/d). The iron metabolism responses to simulated microgravity of the AG training groups did not differ significantly from the responses of controls. Independently from AG, we found that both serum iron concentrations (+31.3%, P = 0.027) and transferrin saturation levels (+28.4%, P = 0.009) increased in males after 6 d of HDT bed rest, as well as serum hepcidin concentrations (+36.9%, P = 0.005). The increase of transferrin saturation levels persisted after 57 d of HDT bed rest (+13.5%, P = 0.026), suggesting that long-term exposure to microgravity sustainably increases serum iron availability in males, and consequently the risk of iron excess or misdistribution. In females, 6 and 57 d of HDT bed rest did not significantly change serum iron, transferrin saturation, or hepcidin levels. The data from this exploratory study suggest that 1) AG training does not influence the iron metabolism responses to microgravity; and 2) iron metabolism parameters, especially iron availability for cells, are significantly increased in males, but not in females, exposed to long-term simulated microgravity. Because of the small sample size of females, we nevertheless must be cautious before concluding that iron metabolism could differently respond to microgravity in females. This trial was registered at https://www.drks.de as DRKS00015677.

Serum iron availability, but not iron stores, is lower in naturally menstruating than in oral contraceptive athletes

ABSTRACT This study measured serum markers of iron status in naturally menstruating and oral contraceptive (OC) athletes during the main hormonal milieus of these two profiles to identify potential differences confounding the diagnosis of iron deficiency in female athletes. Resting blood samples were collected from 36 naturally menstruating athletes during the early-follicular phase (EFP), mid- late-follicular phase (MLFP) and mid-luteal phase (MLP) of the menstrual cycle. Simultaneously, blood samples were collected from 24 OC athletes during the withdrawal and active-pill phase of the OC cycle. Serum iron, ferritin, transferrin, transferrin saturation (TSAT), C-reactive protein (CRP), interleukin-6 and sex hormones were analyzed. Naturally menstruating athletes showed lower levels of TSAT, iron and transferrin than OC athletes when comparing the bleeding phase of both profiles (p<0.05) as well as when comparing all analyzed phases of the menstrual cycle to the active pill phase of the OC cycle (p<0.05). Interestingly, only lower transferrin was found during MLFP and MLP compared to the withdrawal phase of the OC cycle (p>0.05), with all other iron markers showing no differences (p>0.05). Intracycle variations were also found within both types of cycle, presenting reduced TSAT and iron during menstrual bleeding phases (p<0.05). In conclusion, in OC athletes, serum iron availability, but not serum ferritin, seems higher than in naturally menstruating ones. However, such differences are lost when comparing the MLFP and MLP of the menstrual cycle with the withdrawal phase of the OC cycle. This should be considered in the assessment of iron status in female athletes. Highlights Naturally menstruating athletes present lower TSAT, iron and transferrin in all analyzed phases of the menstrual cycle compared to OC athletes during their active pill phase. However, both the mid-late follicular and mid-luteal phases of the menstrual cycle do not differ from the withdrawal phase of the oral contraceptive cycle. Intracycle variations are found for TSAT and iron in both naturally menstruating and oral contraceptive athletes, which are mainly driven by a reduction in TSAT and iron during menstrual bleeding phases. As serum iron availability changes significantly as a function of the athlete's hormonal status, it should be considered in the assessment of the athlete’s iron status as well as standardise the phase of the menstrual cycle in which to assess iron markers to avoid misdiagnosis or misleading results. In contrast, the assessment of iron stores through serum ferritin is substantially stable and the athlete’s hormonal status does not seem to be of relevance for this purpose.

Hypoferremia is Associated With Increased Hospitalization and Oxygen Demand in COVID-19 Patients.

Iron metabolism might play a crucial role in cytokine release syndrome in COVID-19 patients. Therefore, we assessed iron metabolism markers in COVID-19 patients for their ability to predict disease severity. COVID-19 patients referred to the Heidelberg University Hospital were retrospectively analyzed. Patients were divided into outpatients (cohort A, n = 204), inpatients (cohort B, n = 81), and outpatients later admitted to hospital because of health deterioration (cohort C, n = 23). Iron metabolism parameters were severely altered in patients of cohort B and C compared to cohort A. In multivariate regression analysis including age, gender, CRP and iron-related parameters only serum iron and ferritin were significantly associated with hospitalization. ROC analysis revealed an AUC for serum iron of 0.894 and an iron concentration <6 μmol/l as the best cutoff-point predicting hospitalization with a sensitivity of 94.7% and a specificity of 67.9%. When stratifying inpatients in a low- and high oxygen demand group serum iron levels differed significantly between these two groups and showed a high negative correlation with the inflammatory parameters IL-6, procalcitonin, and CRP. Unexpectedly, serum iron levels poorly correlate with hepcidin. We conclude that measurement of serum iron can help predicting the severity of COVID-19. The differences in serum iron availability observed between the low and high oxygen demand group suggest that disturbed iron metabolism likely plays a causal role in the pathophysiology leading to lung injury.

Hypoferremia Predicts Hospitalization and Oxygen Demand in COVID-19 Patients

Background: Disease severity in COVID-19 patients is associated with cytokine release syndrome (CRS). Understanding factors linked to disease severity and identifying early markers that are predictive for the need of hospitalization or oxygen supplementation are highly relevant. Therefore we assessed iron metabolism markers in COVID-19 patients for their ability to predict disease severity. Methods: Patients tested positive for SARS-CoV-2 referred to the Heidelberg University Hospital were retrospectively analyzed. Patients were divided into outpatients never admitted to hospital (cohort A, n=204), inpatients (cohort B,n=81), and outpatients later admitted to hospital because of health deterioration (cohort C,n=23). Findings: Iron metabolism parameters were severely altered in patients of cohort B and C compared to cohort A. In multivariate regression analysis including age, gender, CRP and iron-related parameters only serum iron and ferritin were significantly associated with hospitalization. ROC analysis revealed an AUC for serum iron of 0.894 and an iron concentration <6µmol/l as the best cutoff-point predicting hospitalization. When stratifying inpatients in a low- and high oxygen demand group serum iron level differed significantly between these two groups and showed a high negative correlation with the inflammatory parameters IL-6, procalcitonin, and CRP. Unexpectedly, serum iron levels poorly correlate with the hepcidin. In addition, we analyzed the effect of immunomodulatory therapies on serum iron levels and observed a 1.8-, 2.0-, and 2.3-fold increase one day after treatment with anakinra, tocilizumab, and immunoglobulins, respectively. Interpretation: We conclude that measurement of serum iron can help predicting the severity of COVID-19. The differences in serum iron availability observed between the low and high oxygen demand group suggest that disturbed iron metabolism likely plays a causal role in the pathophysiology leading to lung injury. Funding Statement: MUM acknowledges funding from the Deutsche Forschungsgemeinschaft (SFB1036, SFB1118) and from the Federal Ministry of Education and Research (NephrESA project Nr 031L0191C). Declaration of Interests: There are no potential conflicts of interest. Ethics Approval Statement: The study was approved by the local ethics committee in Heidelberg (ethics approval number S148/2020) and was conducted in accordance with the Declaration of Helsinki.

Iron and stable ischemic heart disease - lessons from heart failure

Iron is an essential element for cardiomyocyte viability and contractility. Systemic iron deficiency, even without anemia, is reflected by iron deficiency in cardiomyocytes. As in other cells, there is here a complex, local and autonomous regulation of iron metabolism, based on two molecular systems: the hepcidin/ferroportin/transferrin receptor-1 axis; and the iron regulatory proteins-1,2 system. These molecular pathways allow cardiomyocytes to react to changes in serum iron availability. In mice, dietary manipulations of serum iron availability or cardio-specific deletions and mutations of regulatory genes for intracellular iron metabolism have clarified some aspects of the causal relationship between cardiomyocyte iron deficiency and the development of severe heart failure, prevented by intravenous iron treatment even without the occurrence of iron deficiency (sideropenic) anemia. The deleterious effects of iron deficiency and hypoxia on gene expression of the main regulators of intracellular iron and oxygen metabolism and on cardiac function are very similar in heart failure and in chronic stable ischemic heart disease, and conjure towards cardiomyocyte injury. We here hypothesize that in non-anemic patients with stable ischemic heart disease a chronic or acute serum iron deficiency can amplify the chronic activation of the cardiomyocyte hypoxia-inducible factor-1α. As a consequence, cardiac adaptative responses to chronic hypoxia/ischemia are significantly impaired, and cardiac dysfunction exacerbated. We hypothesize that, in such patients, iron replacement through forced iron supplementation may replete cardiomyocyte iron deficiency and improve ischemic heart disease. This hypothesis requires further experimental studies, but also, and already now, specific clinical trials.

Components of a new gene family of ferroxidases involved in virulence are functionally specialized in fungal dimorphism

Mucormycosis is an emerging angio-invasive infection caused by Mucorales that presents unacceptable mortality rates. Iron uptake has been related to mucormycosis, since serum iron availability predisposes the host to suffer this infection. In addition, iron uptake has been described as a limiting factor that determines virulence in other fungal infections, becoming a promising field to study virulence in Mucorales. Here, we identified a gene family of three ferroxidases in Mucor circinelloides, fet3a, fet3b and fet3c, which are overexpressed during infection in a mouse model for mucormycosis, and their expression in vitro is regulated by the availability of iron in the culture media and the dimorphic state. Thus, only fet3a is specifically expressed during yeast growth under anaerobic conditions, whereas fet3b and fet3c are specifically expressed in mycelium during aerobic growth. A deep genetic analysis revealed partially redundant roles of the three genes, showing a predominant role of fet3c, which is required for virulence during in vivo infections, and shared functional roles with fet3b and fet3c during vegetative growth in media with low iron concentration. These results represent the first described functional specialization of an iron uptake system during fungal dimorphism.

Elevated Levels of Estrogen Suppress Hepcidin Synthesis and Enhance Serum Iron Availability in Premenopausal Women.

Clinical and experimental observations have long suggested that elevated levels of estrogen associate with increased serum iron availability. Additionally, recent work has shown that estrogen can downregulate hepcidin synthesis in vitro. This study aims at assessing whether the ability of estrogen to downregulate hepcidin synthesis translates into changes in serum iron status. Hepcidin synthesis was evaluated in MCF-7, Hep-G2 and SKOV-3 cells treated with increasing concentrations of estrogen and cultured for up to 24 h post treatment. The correlation between levels of serum estrogen, hepcidin and iron was assessed using serum samples collected from 153 premenopausal women at random and samples collected from 6 women at days 1, 5, 10, 16, 21 and 28 of the monthly cycle. Estrogen-treated MCF-7 cells showed a significant reduction in hepcidin synthesis, especially at 20 nM/24 h E2 treatment. Hepcidin synthesis was also significantly reduced in Hep-G2 and SKOV-3 cells at 20 nM/24 h E2 treatment. In serum samples collected at random, estrogen (P=0.022; R=-0.213) and iron (P=0.028; R=-0.316) correlated negatively with hepcidin and positively with each other (P=0.033; R=0.319). An overall similar pattern was also observed in monthly cycle-timed samples. These findings suggest that elevated levels of estrogen reduce hepcidin synthesis as means of enhancing serum iron content in menstruating women.

Iron Parameters Determine the Prognosis of Critically Ill Patients.

Because iron is both an essential and toxic micronutrient influencing the development of microbial infections, we evaluated the usefulness of iron parameters as outcome predictors in ICU patients. Prospective clinical single-center non-interventional study. General internal medicine ICU; German University hospital. One hundred and twelve septic and 43 nonseptic ICU patients, 156 healthy blood donors. Serum iron parameters at admission were correlated with short and long term mortality in ICU subjects. Both hepcidin and ferritin concentrations were significantly elevated in ICU patients compared with blood donors and were the highest in septic patients. On the contrary, serum iron and transferrin levels were decreased in ICU subjects with lowest values among septic patients. Hepcidin values correlated with ferritin levels, and serum iron correlated strongly with transferrin saturation. A moderate correlation of hepcidin, ferritin, and transferrin with inflammatory parameters was noted. Both short- and long-term survivors displayed higher ferritin/transferrin levels and lower transferrin saturation. In Kaplan-Meier analyses, low iron levels (cutoff 10.5 μmol/mL), low transferrin saturation (cutoff 55%), and high serum transferrin concentrations (cutoff 1.6 g/L) were associated with short- and long-term survival. In the subgroup of septic ICU subjects, low iron levels and transferrin saturation went along with a nonlethal outcome. Our findings demonstrate that parameters of iron metabolism, particularly transferrin saturation, that reflect serum iron availability, are strong outcome predictors in ICU patients. These data suggest that a failure of iron homeostasis with increased iron availability in serum occurs in lethally ill ICU patients and should trigger prospective clinical trials evaluating the usefulness of iron-chelating therapy in critical illness and sepsis.

Increased hepcidin levels in high-altitude pulmonary edema.

Low iron availability enhances hypoxic pulmonary vasoconstriction (HPV). Considering that reduced serum iron is caused by increased erythropoiesis, insufficient reabsorption, or elevated hepcidin levels, one might speculate that exaggerated HPV in high-altitude pulmonary edema (HAPE) is related to low serum iron. To test this notion we measured serum iron and hepcidin in blood samples obtained in previously published studies at low altitude and during 2 days at 4,559 m (HA1, HA2) from controls, individuals with HAPE, and HAPE-susceptible individuals where prophylactic dexamethasone and tadalafil prevented HAPE. As reported, at 4,559 m pulmonary arterial pressure was increased in healthy volunteers but reached higher levels in HAPE. Serum iron levels were reduced in all groups at HA2. Hepcidin levels were reduced in all groups at HA1 and HA2 except in HAPE, where hepcidin was decreased at HA1 but unexpectedly high at HA2. Elevated hepcidin in HAPE correlated with increased IL-6 at HA2, suggesting that an inflammatory response related to HAPE contributes to increased hepcidin. Likewise, platelet-derived growth factor, a regulator of hepcidin, was increased at HA1 and HA2 in controls but not in HAPE, suggesting that hypoxia-controlled factors that regulate serum iron are inappropriately expressed in HAPE. In summary, we found that HAPE is associated with inappropriate expression of hepcidin without inducing expected changes in serum iron within 2 days at HA, likely due to too short time. Although hepcidin expression is uncoupled from serum iron availability and hypoxia in individuals developing HAPE, our findings indicate that serum iron is not related with exaggerated HPV.

Fully Human Anti-Hepcidin Antibodies Mobilize Iron and Treat Inflammatory Anemia in a Mouse Model.

Abstract 626Iron maldistribution has been associated with multiple diseases including atherosclerosis, diabetes, neurodegenerative disorders and the anemia of inflammation (AI). Hepcidin is a 25aa peptide that is the central mediator of iron homeostasis. It is produced in response to inflammation and is implicated in limiting the response to erythropoietin (EPO) even in the presence of adequate body iron stores. To further explore the role of hepcidin in inflammatory anemia, a novel EPO-resistant model of AI was developed in mice and the effects of a high affinity fully human anti-hepcidin antibody (12B9m; 2pM affinity) were examined.Since antibody 12B9m had low affinity for mouse hepcidin (10-20nM), human hepcidin (hHepc) knock-in mice were created. Strains were generated with either the mouse hepc1 gene or both hepc1 and 2 genes replaced with the single hHepc gene (HAMP). To induce inflammation and establish AI, mice were injected intraperitoneally with heat-killed Brucella abortus (BA: 3×108 particles/mouse): a procedure adapted from an inflammatory fatigue model. BA treatment led to increased serum levels of IL-6 (3818 ± 548 pg/ml versus <10 pg/ml in controls, p<0.0001) and hepcidin (216 ± 9 ng/ml versus 99 ± 6 ng/ml, p<0.0001) by 6 hours. Hypoferremia reached a nadir 3 days after BA treatment (total serum iron was 201 ±10 mg/dL versus 370 ± 19 mg/dL in controls, p<0.0001). Mice developed anemia, with hemoglobin (Hb) reaching a nadir 10-14 days after BA and returning to normal by day 28. Treatment with EPO (300 mg/kg 8 days after BA) had no effect on hemoglobin by day 14 (7.6 ± 0.4 g/dL in controls and 7.6 ± 0.5 g/dL with EPO; NS).Treatment with antibody 12B9m (5mg/mouse; n=6) increased serum iron at day 3 (907 ± 47 mg/dL versus 201 ± 10 mg/dL, p<0.0001) in AI mice, and restored response to EPO (day 14 Hb of 10.0 ± 0.4 g/dL versus 7.6 ± 0.5 g/dL for control antibody treatment; p<0.001, n=5). Early iron-dependent red cell parameters such as reticulocyte MCV were also increased (71.5 ± 5.2 fL versus 56.7 ±1.9 fL; p<0.05, n=5/group), presumably due to the increased iron availability. In a larger study, 12B9m treatment alone (without EPO co-administration) led to a significant increase in Hb (10.0 ± 0.5 g/dL versus 8.0 ± 0.3 g/dL for control antibody treatment; p<0.001, n=14/group).Treatment with 12B9m did not affect inflammatory cytokine induction (e.g., IL-6 levels at 6 hours post-BA of 4996 ± 487 pg/ml versus 3818 ± 548 pg/ml in the control antibody group: NS), indicating that neutralization of hepcidin alone was sufficient to allow an effective response to EPO.These data indicated that antibodies which neutralize hepcidin may treat AI by increasing serum iron availability for erythropoiesis. The ability to manipulate iron uptake and redistribution in vivo may also offer promise in other diseases where iron maldistribution is involved. Disclosures:Cooke:Amgen: Employment. Augustic:Amgen: Employment. Sloan:Amgen: Employment. Tran:Amgen: Employment. Arvedson:Amgen: Employment. Juan:Amgen: Employment. Sasu:Amgen: Employment.

Impact of Serum Iron Availability on Hemoglobin and Hemdoynamics in Patients with Advanced Heart Failure

Impact of Serum Iron Availability on Hemoglobin and Hemdoynamics in Patients with Advanced Heart Failure

Impact of Serum Iron Availability on Haemoglobin and Haemdoynamics in Patients with Advanced Heart Failure

Impact of Serum Iron Availability on Haemoglobin and Haemdoynamics in Patients with Advanced Heart Failure

The Epidemiology of Hemoglobin Levels in Patients With Type 2 Diabetes

Anemia is a common finding in patients with diabetes, for whom it constitutes an additional burden. The aim of this study is to clarify the natural history of anemia in patients with type 2 diabetes and describe factors that predict a decrease in hemoglobin (Hb) levels. A 5-year prospective cohort study was designed as a follow-up of 503 individuals with type 2 diabetes in a single diabetes clinic. In addition to standard management, a full blood count was obtained at each routine visit. No intervention was undertaken to modify Hb levels. At baseline, 12% of patients had anemia, and an additional 13% developed anemia during follow-up. Overall Hb levels decreased by -0.07 +/- 0.01 g/dL/y, suggesting that anemia is the end point of a process that begins more than 10 years previously with the initiation of vascular damage. The greatest decreases in Hb levels were seen in patients with macroalbuminuria, renal impairment, or established macrovascular disease at baseline (all P < 0.01). In patients with microvascular disease, decreasing Hb levels tracked with decreasing glomerular filtration rates (GFRs). Patients with an estimated GFR greater than 90 mL/min/1.73 m2 (>1.5 mL/s) or normoalbuminuria had stable Hb levels during the 5-year follow-up. In patients with anemia in our cohort who were managed conservatively, Hb levels decreased by 0.09 +/- 0.03 g/dL/y. This decrease was associated with HbA1c levels, but not renal function. This study defines the natural history of Hb levels in patients with type 2 diabetes. Early identification of anemia may be achieved by means of annual or biannual screening in high-risk groups with nephropathy, advanced age, or macrovascular disease. These data are important for developing a rational response to the prevention and management of anemia.