Early effects of erythropoietin on serum hepcidin and serum iron bioavailability in healthy volunteers

Indirect biomarkers of blood doping: A systematic review

The detection of blood doping represents a current major issue in sports and an ongoing challenge for antidoping research. Initially focusing on direct detection methods to identify a banned substance or its metabolites, the antidoping effort has been progressively complemented by indirect approaches. The longitudinal and individual monitoring of specific biomarkers aims to identify nonphysiological variations that may be related to doping practices. From this perspective, the identification of markers sensitive to erythropoiesis alteration is key in the screening of blood doping. The current Athlete Biological Passport implemented since 2009 is composed of 14 variables (including two primary markers, i.e., hemoglobin concentration and OFF score) for the hematological module to be used for indirect detection of blood doping. Nevertheless, research has continually proposed and investigated new markers sensitive to an alteration of the erythropoietic cascade and specific to blood doping. If multiple early markers have been identified (at the transcriptomic level) or developed directly in a diagnostics' kit (at a proteomic level), other target variables at the end of the erythropoietic process (linked with the red blood cell functions) may strengthen the hematological module in the future. Therefore, this review aims to provide a global systematic overview of the biomarkers considered to date in the indirect investigation of blood doping.

Contemporary blood doping-Performance, mechanism, and detection

Blood doping is prohibited for athletes but has been a well-described practice within endurance sports throughout the years. With improved direct and indirect detection methods, the practice has allegedly moved towards micro-dosing, that is, reducing the blood doping regime amplitude. This narrative review evaluates whether blood doping, specifically recombinant human erythropoietin (rhEpo) treatment and blood transfusions are performance-enhancing, the responsible mechanism as well as detection possibilities with a special emphasis on micro-dosing. In general, studies evaluating micro-doses of blood doping are limited. However, in randomized, double-blinded, placebo-controlled trials, three studies find that infusing as little as 130 ml red blood cells or injecting 9 IU × kg bw-1 rhEpo three times per week for 4 weeks improve endurance performance ~4%-6%. The responsible mechanism for a performance-enhancing effect following rhEpo or blood transfusions appear to be increased O2 -carrying capacity, which is accompanied by an increased muscular O2 extraction and likely increased blood flow to the working muscles, enabling the ability to sustain a higher exercise intensity for a given period. Blood doping in micro-doses challenges indirect detection by the Athlete Biological Passport, albeit it can identify ~20%-60% of the individuals depending on the sample timing. However, novel biomarkers are emerging, and some may provide additive value for detection of micro blood doping such as the immature reticulocytes or the iron regulatory hormones hepcidin and erythroferrone. Future studies should attempt to validate these biomarkers for implementation in real-world anti-doping efforts and continue the biomarker discovery.

mTOR Inhibitors Induce Erythropoietin Resistance in Renal Transplant Recipients

Aim

To elucidate the role of mTOR inhibitors on iron, hepcidin and erythropoietin-mediated regulation of hemopoiesis in stable renal transplant recipients (RTR).

Background

Impaired hemopoiesis is common following renal transplantation managed using mTOR inhibitors. The mechanisms responsible are uncertain but include direct effects on iron, hepcidin or erythropoietin-mediated hemopoiesis.

Methods

We conducted a single center prospective case-control study of 26 adult RTR with stable allograft function. RTR received stable mTOR dosing (cases, 11/26 [42%]) or stable tacrolimus dosing (controls, 15/26 [58%]). Baseline demographics, full blood count, renal function, iron studies, hepcidin-25, Interleukin-6 (IL-6) and erythropoietin (EPO) levels were determined.

Results

There were no differences in age, gender or allograft function. Mean daily sirolimus dose for cases was 1.72 mg, with mean trough level of 8.46 ng/mL. Mean daily tacrolimus dose for controls was 4.3 mg, with mean trough level of 5.8 ng/mL. There were no differences in mean hemoglobin (143 vs. 147 g/L; p = 0.59), MCV (88 vs. 90 fL; p = 0.35), serum ferritin (150 vs. 85.7 μg/L; p = 0.06), transferrin saturation (26 vs. 23.3%; p = 0.46), IL-6 (11 vs. 7.02 pg/ml; p = 0.14) or hepcidin-25 (3.62 vs. 3.26 nM; p = 0.76) between the groups. EPO levels were significantly higher in the group receiving mTOR therapy (16.8 vs. 8.49 IU/L; p = 0.028). On logistic regression analysis EPO level was the only variable that had a significant impact providing an odds ratio of 0.84 (95%CI 0.66–0.98). The area under the receiver operator characteristic curve (ROC) for the analysis was 0.77 (95%CI 0.54–0.94) with p = 0.04.

Conclusion: Higher levels of EPO in the absence of deranged iron biochemistry or hepcidin-25 levels suggest that EPO resistance rather than impaired iron metabolism may contribute to the impaired hemopoiesis previously demonstrated in RTR on mTOR therapy.

Effects of altitude and recombinant human erythropoietin on iron metabolism: a randomized controlled trial

Current markers of iron deficiency (ID), such as ferritin and hemoglobin, have shortcomings, and hepcidin and erythroferrone (ERFE) could be of clinical relevance in relation to early assessment of ID. Here, we evaluate whether exposure to altitude-induced hypoxia (2,320 m) alone, or in combination with recombinant human erythropoietin (rHuEPO) treatment, affects hepcidin and ERFE levels before alterations in routine ID biomarkers and stress erythropoiesis manifest. Two interventions were completed, each comprising a 4-wk baseline, a 4-wk intervention at either sea level or altitude, and a 4-wk follow-up. Participants (n = 39) were randomly assigned to 20 IU·kg body wt^-1 rHuEPO or placebo injections every second day for 3 wk during the two intervention periods. Venous blood was collected weekly. Altitude increased ERFE (P ≤ 0.001) with no changes in hepcidin or routine iron biomarkers, making ERFE of clinical relevance as an early marker of moderate hypoxia. rHuEPO treatment at sea level induced a similar pattern of changes in ERFE (P < 0.05) and hepcidin levels (P < 0.05), demonstrating the impact of accelerated erythropoiesis and not of other hypoxia-induced mechanisms. Compared with altitude alone, concurrent rHuEPO treatment and altitude exposure induced additive changes in hepcidin (P < 0.05) and ERFE (P ≤ 0.001) parallel with increases in hematocrit (P < 0.001), demonstrating a relevant range of both hepcidin and ERFE. A poor but significant correlation between hepcidin and ERFE was found (R² = 0.13, P < 0.001). The findings demonstrate that hepcidin and ERFE are more rapid biomarkers of changes in iron demands than routine iron markers. Finally, ERFE and hepcidin may be sensitive markers in an antidoping context.

A Perspective on Erythropoietin as a Potential Adjuvant Therapy for Acute Lung Injury/Acute Respiratory Distress Syndrome in Patients with COVID-19

The novel coronavirus 2019-nCoV (SARS-CoV-2) infection that emerged in China in December 2019 has rapidly spread to become a global pandemic. This article summarizes the potential benefits of erythropoietin (EPO) in alleviating SARS-CoV-2 pathogenesis which is now called COVID-19. As with other coronavirus infection, the lethality of COVID-19 is associated with respiratory dysfunction due to overexpression of proinflammatory cytokines induced by the host immune responses. The resulting cytokine storm leads to the development of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Erythropoietin, well known for its role in the regulation of erythropoiesis, may have protective effects against ALI/ARDS induced by viral and other pathogens. EPO exerts antiapoptotic and cytoprotective properties under various pathological conditions. With a high safety profile, EPO promotes the production of endothelial progenitor cells and reduce inflammatory processes through inhibition of the nuclear factor-κB (NF-κB) and JAK-STAT3 signaling pathways. Thus, it may be considered as a safe drug candidate for COVID-19 patients if given at the early stage of the disease. The potential effects of erythropoietin on different aspects of ALI/ARDS associated with SARS-CoV-2 infection are reviewed.

Erythropoietic regulators of iron metabolism

Erythropoiesis is the predominant consumer of iron in humans and other vertebrates. By decreasing the transcription of the gene encoding the iron-regulatory hormone hepcidin, erythropoietic activity stimulates iron absorption, as well as the release of iron from recycling macrophages and from stores in hepatocytes. The main erythroid regulator of hepcidin is erythroferrone (ERFE), synthesized and secreted by erythroblasts in the marrow and extramedullary sites. The production of ERFE is induced by erythropoietin (EPO) and is also proportional to the total number of responsive erythroblasts. ERFE acts on hepatocytes to suppress the production of hepcidin, through an as yet unknown mechanism that involves the bone morphogenetic protein pathway. By suppressing hepcidin, ERFE facilitates iron delivery during stress erythropoiesis but also contributes to iron overload in anemias with ineffective erythropoiesis. Although most of these mechanisms have been defined in mouse models, studies to date indicate that the pathophysiology of ERFE is similar in humans. ERFE antagonists and mimics may prove useful for the prevention and treatment of iron disorders.

Erythropoietin as a performance-enhancing drug: Its mechanistic basis, detection, and potential adverse effects

Erythropoietin (EPO) is the main hormone regulating red blood cell (RBC) production. The large-scale production of a recombinant human erythropoietin (rHuEPO) by biotechnological methods has made possible its widespread therapeutic use as well as its misuse in sports. Since the marketing of the first epoetin in 1989, the development has progressed to the third-generation analogs. However, the production of rHuEPO is costly, and the frequent administration of an injectable formula is not optimal for compliance of therapeutic patients. Hence, pharmaceutical industries are currently developing alternative approaches to stimulate erythropoiesis, which might offer new candidates for doping purposes. The hypoxia inducible factors (HIF) pathway is of particular interest. The introduction of new erythropoiesis-stimulating agents (ESAs) for clinical use requires subsequent development of anti-doping methods for detecting the abuse of these substances. The detection of ESAs is based on two different approaches, namely, the direct detection of exogenous substances and the indirect detection, for which the effects of the substances on specific biomarkers are monitored. Omics technologies, such as ironomics or transcriptomics, are useful for the development of new promising biomarkers for the detection of ESAs. Finally, the illicit use of ESAs associates with multiple health risks that can be irreversible, and an essential facet of anti-doping work is to educate athletes of these risks. The aim of this review is to provide an overview of the evolution of ESAs, the research and implementation of the available detection methods, and the side effects associated with the misuse of ESAs.

Relationship between the Ingestion of a Polyphenol-Rich Drink, Hepcidin Hormone, and Long-Term Training

The effects of polyphenol-rich foods on the iron status of athletes, as well as the effect of physical training on the hormone hepcidin, implicated in iron metabolism, are not clear. We investigated the influence on iron metabolism of a long-term training intervention of 120 days, measuring the hepcidin concentration in the plasma of 16 elite triathletes, and the effect of the ingestion of 200 mL of either aronia-citrus juice or a placebo drink for 45 days, in a crossover design. The highest plasma hepcidin concentrations were observed at the beginning of the study (116 ± 63 nM) and levels steadily decreased until the end of the intervention (final value 10 ± 7.5 nM). Long-term training might reduce inflammation and, hence, could be responsible for the decrease in hepcidin in triathletes. Polyphenols from aronia-citrus juice did not interfere in iron absorption, as we did not observe significant differences between the intake of the placebo drink or juice with regard to hepcidin levels. Further studies are required to ascertain the time and conditions necessary to restore hepcidin levels, which reflect the iron status of triathletes.

Joint Model of Iron and Hepcidin During the Menstrual Cycle in Healthy Women

Hepcidin regulates serum iron levels, and its dosage is used in differential diagnostic of iron-related pathologies. We used the data collected in the HEPMEN (named after HEPcidin during MENses) study to investigate the joint dynamics of serum hepcidin and iron during the menstrual cycle in healthy women. Ninety menstruating women were recruited after a screening visit. Six fasting blood samples for determination of iron-status variables were taken in the morning throughout the cycle, starting on the second day of the period. Non-linear mixed effect models were used to describe the evolution of iron and hepcidin. Demographic and medical covariates were tested for their effect on model parameters. Parameter estimation was performed using the SAEM algorithm implemented in the Monolix software. A general pattern was observed for both hepcidin and iron, consisting of an initial decrease during menstruation, followed by a rebound and stabilising during the second half of the cycle. We developed a joint model including a menstruation-induced decrease of both molecules at the beginning of the menses and a rebound effect after menses. Iron stimulated the release of hepcidin. Several covariates, including contraception, amount of blood loss and ferritin, were found to influence the parameters. The joint model of iron and hepcidin was able to describe the fluctuations induced by blood loss from menstruation in healthy non-menopausal women and the subsequent regulation. The HEPMEN study showed fluctuations of iron-status variables during the menstrual cycle, which should be considered when using hepcidin measurements for diagnostic purposes in women of child-bearing potential.

Iron and oxygen sensing: a tale of 2 interacting elements?

Iron and oxygen metabolism are intimately linked with one another.

The Role of the Multiple Hormonal Dysregulation in the Onset of "Anemia of Aging": Focus on Testosterone, IGF-1, and Thyroid Hormones

Anemia is a multifactorial condition whose prevalence increases in both sexes after the fifth decade of life. It is a highly represented phenomenon in older adults and in one-third of cases is "unexplained." Ageing process is also characterized by a "multiple hormonal dysregulation" with disruption in gonadal, adrenal, and somatotropic axes. Experimental studies suggest that anabolic hormones such as testosterone, IGF-1, and thyroid hormones are able to increase erythroid mass, erythropoietin synthesis, and iron bioavailability, underlining a potential role of multiple hormonal changes in the anemia of aging. Epidemiological data more consistently support an association between lower testosterone and anemia in adult-older individuals. Low IGF-1 has been especially associated with anemia in the pediatric population and in a wide range of disorders. There is also evidence of an association between thyroid hormones and abnormalities in hematological parameters under overt thyroid and euthyroid conditions, with limited data on subclinical statuses. Although RCTs have shown beneficial effects, stronger for testosterone and the GH-IGF-1 axis and less evident for thyroid hormones, in improving different hematological parameters, there is no clear evidence for the usefulness of hormonal treatment in improving anemia in older subjects. Thus, more clinical and research efforts are needed to investigate the hormonal contribution to anemia in the older individuals.

Regulation of Hepcidin-25 by Short- and Long-Acting rhEPO May Be Dependent on Ferritin and Predict the Response to rhEPO in Hemodialysis Patients

Background/Aims

We examined whether regulation of hepcidin-25 by short- or long-acting recombinant human erythropoietin (rhEPO) is dependent on ferritin and predicts the response to rhEPO in hemodialysis (HD) patients.

Methods

Two studies with rhEPO were performed in 9 HD patients with a 2-year interval. Serum hepcidin-25 was measured at 0-18 h after intravenous epoetin-β (EPO) or methoxy polyethylene glycol-epoetin-β (PEG-EPO) administration and on days 3-7 after PEG-EPO. Hemoglobin (Hb), serum ferritin, transferrin, C-reactive protein (CRP), and interleukin (IL)-6 were analyzed before hepcidin measurement and 6 months after rhEPO. Based on the serum ferritin levels before hepcidin measurement, the patients in the two studies with EPO or PEG-EPO were combined into low (11; serum ferritin of <15.0 ng/ml) and high ferritin groups (7; serum ferritin of ≥15.0 ng/ml). The response of hepcidin-25 to rhEPO and the effect of rhEPO on anemia were compared between the groups.

Results

The serum hepcidin-25 levels rose at 6-9 h and returned to the baseline at 18 h after EPO. They rose at 6-9 h, returned to the baseline at 18 h, and decreased on day 5-7 after PEG-EPO. Serum hepcidin-25 levels were low (<5.0 ng/ml) in the low ferritin group, but rose at 6-9 h after rhEPO in the high ferritin group. Serum transferrin levels were similar, and CRP and IL-6 were normal in both groups. Hb tended to increase in the low ferritin group, but it significantly decreased in the high ferritin group after rhEPO.

Conclusion

Regulation of hepcidin-25 by rhEPO may be dependent on ferritin, affecting the response to rhEPO in HD patients.

Serum hepcidin levels and muscle iron proteins in humans injected with low- or high-dose erythropoietin

Inhibition of hepcidin expression by erythropoietic signals is of great physiological importance; however, the inhibitory pathways remain poorly understood. To investigate (i) the direct effect of erythropoietin (Epo) and (ii) the contribution of putative mediators on hepcidin repression, healthy volunteers were injected with a single dose of Epo, either low (63 IU/kg, n = 8) or high (400 IU/kg, n = 6). Low-dose Epo provoked hepcidin down-modulation within 24 h; the effect was not immediate as hepcidin circadian variations were still present following injection. High-dose Epo induced no additional effect on the hepcidin response, that is hepcidin diurnal fluctuations were not abolished in spite of extremely high Epo levels. We did not find significant changes in putative mediators of hepcidin repression, such as transferrin saturation, soluble transferrin receptor, or growth differentiation factor 15. Furthermore, the potential hepcidin inhibitor, soluble hemojuvelin, was found unaltered by Epo stimulation. This finding was consistent with the absence of signs of iron deficiency observed at the level of skeletal muscle tissue. Our data suggest that hepcidin repression by erythropoietic signals in humans may not be controlled directly by Epo, but mediated by a still undefined factor.

Testosterone administration inhibits hepcidin transcription and is associated with increased iron incorporation into red blood cells

Testosterone administration increases hemoglobin levels and has been used to treat anemia of chronic disease. Erythrocytosis is the most frequent adverse event associated with testosterone therapy of hypogonadal men, especially older men. However, the mechanisms by which testosterone increases hemoglobin remain unknown. Testosterone administration in male and female mice was associated with a greater increase in hemoglobin and hematocrit, reticulocyte count, reticulocyte hemoglobin concentration, and serum iron and transferrin saturation than placebo. Testosterone downregulated hepatic hepcidin mRNA expression, upregulated renal erythropoietin mRNA expression, and increased erythropoietin levels. Testosterone-induced suppression of hepcidin expression was independent of its effects on erythropoietin or hypoxia-sensing mechanisms. Transgenic mice with liver-specific constitutive hepcidin over-expression failed to exhibit the expected increase in hemoglobin in response to testosterone administration. Testosterone upregulated splenic ferroportin expression and reduced iron retention in spleen. After intravenous administration of transferrin-bound (58) Fe, the amount of (58) Fe incorporated into red blood cells was significantly greater in testosterone-treated mice than in placebo-treated mice. Serum from testosterone-treated mice stimulated hemoglobin synthesis in K562 erythroleukemia cells more than that from vehicle-treated mice. Testosterone administration promoted the association of androgen receptor (AR) with Smad1 and Smad4 to reduce their binding to bone morphogenetic protein (BMP)-response elements in hepcidin promoter in the liver. Ectopic expression of AR in hepatocytes suppressed hepcidin transcription; this effect was blocked dose-dependently by AR antagonist flutamide. Testosterone did not affect hepcidin mRNA stability. In conclusion, testosterone inhibits hepcidin transcription through its interaction with BMP/Smad signaling. Testosterone administration is associated with increased iron incorporation into red blood cells.

SPR detection of human hepcidin-25: a critical approach by immuno- and biomimetic-based biosensing

The human hepcidin-25 hormone has a key role in iron regulation in blood. The clinical relevance of this hepatic ~2.8 kDa cysteine-rich peptide is rapidly increasing, since altered levels can be associated with inflammatory events and iron dysfunctions, such as hereditary hemochromatosis and iron overload. Moreover, hepcidin has also attracted the anti-doping field for its possible role as indirect marker of erythropoietin blood doping. Methods currently reported are based on immunoassays (ELISA and RIA), or various types of mass spectroscopy (MS)-based protocols, semi-quantitative or quantitative. Despite the great effort in optimizing robust and simple assays measuring hepcidin in real matrices, at present this challenge remains still an open issue. To explore the possibility to face hepcidin detection through the development of affinity-based biosensors, we set up a comparative study by surface plasmon resonance (SPR) technology. An immuno-based, on anti-hepcidin-25 IgG, and a biomimetic-based, on a synthetic peptide corresponding to the hepcidin-binding site on ferroportin (HBD), biosensors were developed. Here we report behaviors and analytical performances of the two systems, discussing limits and potentialities.