The ontogeny of the biological role and production of erythropoietin

Umbilical Cord Erythroferrone Is Inversely Associated with Hepcidin, but Does Not Capture the Most Variability in Iron Status of Neonates Born to Teens Carrying Singletons and Women Carrying Multiples

BACKGROUND

The developing fetus requires adequate iron and produces its own hormones to regulate this process. Erythroferrone (ERFE) is a recently identified iron regulatory hormone, and normative data on ERFE concentrations and relations between iron status and other iron regulatory hormones at birth are needed.

OBJECTIVES

The objective of this study was to characterize cord ERFE concentrations at birth and assess interrelations between ERFE, iron regulatory hormones, and iron status biomarkers in 2 cohorts of newborns at higher risk of neonatal anemia.

METHODS

Umbilical cord ERFE concentrations were measured in extant serum samples collected from neonates born to women carrying multiples (age: 21-43 y; n = 127) or teens (age: 14-19 y; n = 164). Relations between cord blood ERFE and other markers of iron status or erythropoiesis in cord blood were assessed by linear regression and mediation analysis.

RESULTS

Cord ERFE was detectable in all newborns delivered between 30 and 42 weeks of gestation, and mean concentration at birth was 0.73 ng/mL (95% CI: 0.63, 0.85 ng/mL). Cord ERFE was on average 0.25 ng/mL lower in newborns of black as opposed to white ancestry (P = 0.04). Cord ERFE was significantly associated with transferrin receptor (β: 1.17, P < 0.001), ferritin (β: -0.27, P < 0.01), and hemoglobin (Hb) (β: 0.04, P < 0.05). However, cord hepcidin and the hepcidin:erythropoietin (EPO) ratio captured the most variance in newborn iron and hematologic status (>25% of variance explained).

CONCLUSIONS

Neonates born to teens and women carrying multiples were able to produce ERFE in response to neonatal cord iron status and erythropoietic demand. ERFE, however, did not capture significant variance in newborn iron or Hb concentrations. In these newborns, cord hepcidin and the hepcidin:EPO ratio explained the most variance in iron status indicators at birth.

Endogenous erythropoietin varies significantly with inflammation-related proteins in extremely premature newborns

INTRODUCTION

Erythropoietin, a pluripotent glycoprotein essential for erythropoiesis, fetal growth, and development, has recently been implicated in innate immune regulation. Data from the ELGAN Study allowed us to evaluate relationships between endogenous erythropoietin and 25 inflammation-related proteins in extremely premature newborns.

METHODS

We measured the concentrations of 25 inflammation-related proteins and of erythropoietin in blood spots collected on postnatal days 1, 7, and 14 from 936 infants born before 28 weeks gestation. We calculated the odds that infants with an inflammation-related protein in the highest quartile for gestational age and collection day had an erythropoietin concentration in the highest or lowest quartile.

RESULTS

The proportion of children with inflammation-associated protein concentrations in the top quartile tended to increase monotonically with increasing quartile of EPO concentrations on 2 of the 3 days assessed. To a large extent, on each of the 3 days assessed, the odds ratios for an erythropoietin concentration in the top quartile were significantly elevated among those with an inflammation-related protein concentration in the top quartile.

CONCLUSIONS

Our findings suggest that in very preterm newborns, circulating levels of endogenous erythropoietin vary significantly with circulating levels of inflammation-related proteins. Elevation of endogenous erythropoietin might not be an epiphenomenon, but instead might contribute to subsequent events, by either promoting or reducing inflammation, or by promoting an anti-injury or repair capability.

Analysis about the influence on the fetus infected with parvovirus B19 using amniotic erythropoietin and troponin-T

OBJECTIVE

We tried to identify the influence on the fetus infected with parvovirus B19 (PB19) and retrospectively analyze the severity of fetal infection.

METHODS

Twenty pregnant women who developed maternal PB19 infection were included in this study. A total of 20 amniotic fluid samples were collected for measurement of PB19-DNA, erythropoietin (Epo) and troponin-T (TnT).

RESULTS

Of the 5 fetuses with hydrops, 2 were rescued by fetal therapy. Significant differences between groups were found for Epo and TnT: Epo 107.1 ± 45.3 mU/ml and TnT 0.040 ± 0.028 ng/ml (mean ± standard deviation) for the symptomatic fetus group; and Epo 18.9 ± 13.7 mU/ml and TnT 0.008 ± 0.014 ng/ml for the asymptomatic fetus group (p = 0.043 for both variables). Setting Epo ≥50 mU/ml as the predictor of disease onset resulted in an Odds ratio of 56.0, with a 95 % confidence interval of 7.68-1,108.76.

CONCLUSION

The study has determined an amniotic Epo level of ≥50 mU/ml as a factor of the influence on the fetus infected with PB19. The measurement of amniotic Epo level combined with amniotic TnT level is effective for determining the severity of fetal hypoxia.

Increased fetal plasma and amniotic fluid erythropoietin concentrations: markers of intrauterine hypoxia

Tissue hypoxia is the major stimulus of erythropoietin (EPO) synthesis in fetuses and adults. Since EPO does not cross the placenta and is not stored, fetal plasma and amniotic fluid levels indicate EPO synthesis and elimination. Acutely, the rate and magnitude of the increase in plasma EPO levels correlate with the intensity of hypoxia. Amniotic fluid EPO levels correlate with cord plasma levels in normal and abnormal pregnancies, with fetal plasma EPO levels in humans averaging 2.6 times higher than the corresponding amniotic fluid EPO levels. Recent experimental and clinical studies demonstrate that EPO has neuroprotective effects related to its anti-apoptotic and vascular growth-promoting properties. Although under basal conditions the fetal kidneys are the main site of EPO production, during hypoxia recent experimental data indicate an important role of the placenta. Amniotic fluid EPO levels have been shown to increase exponentially during fetal hypoxia in preeclamptic, diabetic and Rh-immunized pregnancies, to correlate inversely with cord blood pH, pO(2) and base excess and to predict neonatal morbidities and NICU admission. As an indicator of chronic intrauterine hypoxia, fetal EPO measurements have increased our knowledge about the pathogenesis and importance of intrauterine growth restriction, macrosomia, diabetic pregnancy, prolonged pregnancy, meconium staining, fetal hemorrhage, fetal anemia, maternal smoking and alcohol consumption, abnormal fetal heart rate and abnormal Doppler flow patterns. While the clinical utility of fetal amniotic fluid and plasma EPO measurements in the management of high-risk pregnancies and their offspring is promising, adequately powered clinical trials are urgently needed.

Pharmacokinetic/Pharmacodynamic Analysis of Paradoxal Regulation of Erythropoietin Production in Acute Anemia

The regulatory mechanism responsible for a paradoxal, rapid drop in the erythropoietin (EPO) plasma level seen 2 to 4 days after acute, phlebotomy-induced anemia was investigated in seven adult sheep. To introduce acute anemia, each sheep underwent two phlebotomies where the hemoglobin (Hb) was reduced to 3 or 4 g/dl over 4 to 5 h. The phlebotomies were spaced 4 to 6 weeks apart in three animals, and 8 days apart in four other animals. EPO plasma levels, reticulocyte count, Hb, and p50 for oxygen-Hb dissociation were determined from frequent blood samplings throughout the study period. EPO's disposition pharmacokinetic (PK) and plasma clearance were determined from i.v. bolus injections of tracer amounts of a recombinant human EPO tracer. The controlled drop in Hb resulted in a rapid increase in plasma EPO to 836 +/- 52 mU/ml (mean +/- coefficient of variation percentage) that was followed by a paradoxical rapid drop 2 to 4 days after the phlebotomy while the animals were still very anemic (Hb = 4.3 +/- 15 g/dl). The rapid drop in plasma EPO level could not be explained by the up-regulated clearance (clearance increased by a factor of less than 2.5) or by physiological adaptation (no change in p50, p > 0.05, second phlebotomy to Hb = 3g/dl inadequately stimulated the EPO production). The PK/pharmacodynamic (PD) analysis supports the hypothesis of a limited sustained high EPO production rate in acute anemia, which indicates an apparent deficiency in the regulation of EPO production in acute anemia. The hypothesis was supported by a PK/PD feedback inhibition model that showed good agreement with the data (r = 0.973 +/- 1.57).

Mechanisms of erythropoietin-induced brain protection in neonatal hypoxia-ischemia rat model

Erythropoietin, a hemotopoietic growth factor, has brain protective actions. This study investigated the mechanisms of Recombinant Human EPO (rhEPO)-induced brain protection in neonates. An established rat hypoxia-ischemia model was used by ligation of the right common carotid artery of 7-day-old pups, followed by 90 minute of hypoxia (8% 02 and 92% N2) at 37 degrees C. Animals were divided into three groups: control, hypoxia-ischemia, and hypoxia-ischemia plus rhEPO treatment. In rhEPO treated pups, 300 units rhEPO was administered intraperitoneally 24 hours before hypoxia. rhEPO treatment (300 units) was administered daily for an additional 2 days. ELISA and immunohistochemistry examined the expression of EPO and EPOR. Brain weight, morphology, TUNEL assay, and DNA laddering evaluated brain protection. rhEPO abolished mortality (from 19% to 0%) during hypoxia insult, increased brain weight from 52% to 88%, reduced DNA fragmentation, and decreased TUNEL-positive cells. Real-time RT-PCR, Western blot, and immunohistochemistry revealed an enhanced expression of heat shock protein 27 (HSP27) in ischemic brain hemisphere. Double labeling of TUNEL with HSP27 showed most HSP27 positive cells were negative to TUNEL staining. rhEPO reduces brain injury, especially apoptotic cell death after neonatal hypoxia-ischemia, partially mediated by the activation of HSP27.

17Beta-estradiol decreases hypoxic induction of erythropoietin gene expression

Exposure to chronic hypoxia induces erythropoietin (EPO) production to facilitate oxygen delivery to hypoxic tissues. Previous studies from our laboratory found that ovariectomy (OVX) exacerbates the polycythemic response to hypoxia and treatment with 17beta-estradiol (E2-beta) inhibits this effect. We hypothesized that E2-beta decreases EPO gene expression during hypoxia. Because E2-beta can induce nitric oxide (NO) production and NO can attenuate EPO synthesis, we further hypothesized that E2-beta inhibition of EPO gene expression is mediated by NO. These hypotheses were tested in OVX catheterized rats treated with E2-beta (20 microg/day) or vehicle for 14 days and exposed to 8 or 12 h of hypoxia (12% O(2)) or normoxia. We found that E2-beta treatment significantly decreased EPO synthesis and gene expression during hypoxia. E2-beta treatment did not induce endothelial NO synthase (eNOS) expression in the kidney but potentiated hypoxia-induced increases in plasma nitrates. We conclude that E2-beta decreases hypoxic induction of EPO. However, this effect does not appear to be related to changes in renal eNOS expression.

Erythropoietin mRNA expression in pig embryos

To address whether altered erythropoietin (EPO) synthesis might be involved in prenatal pig mortality, studies were conducted to measure porcine embryonic EPO mRNA expression during early gestation (days 24-40). Three pig models differing in embryonic survival from days 24-40 were investigated: intact white crossbred gilts (INT), white crossbred gilts that were unilaterally hysterectomized-ovariectomized before puberty and whose pregnant uterus constituted a crowded environment (UHO), and prolific, intact Meishan gilts (ME). A partial cDNA for porcine EPO, developed via reverse transcription and polymerase chain reaction procedures was used to generate a 32P-labeled probe for use in Northern analyses. In an initial study, embryonic liver EPO mRNA was greatest on day 24, decreased by day 30 (P<0.01), and was barely detectable by day 40. EPO mRNA expression was not influenced by pig model. Placental EPO mRNA expression was detectable in only 4 of 53 placentae examined. In a second study at day 35 of gestation, embryonic liver EPO mRNA expression was measured in the same three pig models and in two embryos of divergent weights from each gilt. Meishan embryos had lower (P<0.01) plasma immunoassayable EPO concentrations (P=0.04) and higher survival rates (87+/-2.7%) at day 35 than did white crossbred embryos (75+/-5%). Liver EPO mRNA expression did not differ among animal models, nor did plasma EPO or tissue EPO mRNA expression differ between large and small embryos. There was no apparent relationship between embryonic development, measured as embryonic and placental size, and plasma EPO concentrations or liver EPO mRNA expression. These results indicate that at the gestational ages examined, the embryonic liver is one source of plasma erythropoietin and suggest that at the ages sampled, EPO is not a limiting factor in embryonic development.

Recombinant human erythropoietin treatment of postpartum anemia. Preliminary results

OBJECTIVES

The aim of this study was to investigate the efficacy of recombinant human erythropoietin (rHuEpo) in postpartum anemia.

STUDY DESIGN

At the University Hospital of Ioannina, rHuEpo was administrated subcutaneously to twenty anemic women (hemoglobin [Hb]<10 g/dl), for 15 days following delivery; all were given iron and folic acid per os. Twenty other women (the control group) with postpartum anemia (Hb<10 g/dl), received only iron and folic acid. The Mann-Whitney U-test was used for the comparison of hematological indices between the two groups, on days 1, 3, 5, 10, 15 and 40 postdelivery.

RESULTS

On day 3, reticulocyte counts were significantly higher in the women who received rHuEpo, as compared to the controls (P<0.05). The mean Hb value increased to >2 g/dl in the group undergoing rHuEpo therapy as compared to 0.7 g/dl in the control group on day 5 (P<0.05). Furthermore, two women in the control group required blood transfusions, while no transfusions were required by the rHuEpo group.

CONCLUSIONS

rHuEpo administration is useful for a more rapid amelioration of hematological indices in women with postpartum anemia. Further, the dose given in this study was not associated with significant side-effects.

Erythropoietin in obstetrics

Our objective was to discuss the role of erythropoietin in fetal erythropoiesis and to review its clinical uses in perinatal medicine. All relevant articles compiled through a MEDLINE search (years 1986-1997) were reviewed. Erythropoietin is essential for fetal erythropoiesis and is produced in response to hypoxia and anemia. Cord blood erythropoietin is purely fetal and reflects tissue oxygenation. It has been found to be increased in many complicated pregnancies with underlying fetal hypoxia. Erythropoietin could be used as a marker of fetal hypoxia because its concentration rises rapidly by increased production in response to hypoxia. Its measurement might enable more accurate timing of hypoxic injury. In addition, erythropoietin levels have been well correlated with perinatal brain damage and may facilitate treatment of high risk neonates. Erythropoietin has also been used successfully in anemia of prematurity, decreasing the transfusion requirement. However, studies are still needed to determine the optimal doses of erythropoietin and iron supplementations required for maximizing the red blood cell response. Erythropoietin has been examined as potential maternal therapy in various disorders during pregnancy. These include end-stage renal disease, severe antepartum iron deficiency anemia, and postpartum anemia. Erythropoietin has been found to be effective and well tolerated in these conditions. An additional promising use lies in the optimization of maternal red blood cell mass to allow autologous blood donation. This may be critical in cases where a large amount of bleeding might be anticipated, as with placenta previa. This would also minimize the donor transfusion-related hazards. Erythropoietin with its wide clinical applications could improve maternal and neonatal outcome.

Human Hematopoietic Progenitors Express Erythropoietin

Erythropoietin (EPO) is a factor essential for erythroid cell proliferation, differentiation, and survival. The production of EPO by the kidneys in response to hypoxia and anemia is well documented. To determine whether EPO is also produced by hematopoietic cells, we analyzed the expression of EPO in normal human hematopoietic progenitors and in their progeny. Undifferentiated CD34+lin− hematopoietic progenitors do not have detectable EPO mRNA. Differentiating CD34+ cells that are stimulated with recombinant human EPO in serum-free liquid cultures express both EPO and EPO receptor (EPOR). Because CD34+ cells represent a heterogeneous cell population, we analyzed individual burst-forming units–erythroid (BFU-E) and nonerythroid colony-forming unit–granulocyte-macrophage colonies for EPO mRNA. Only BFU-E colonies were positive for EPO mRNA. Lysates from pooled BFU-E colonies stained positively for EPO by immunoblotting. To further confirm the intrinsic nature of erythroid EPO, we replaced extrinsic EPO in erythroid colony cultures with EPO-mimicking peptide (EMP). We show EPO expression in the EMP-stimulated BFU-Es at both mRNA and protein levels. Stimulation of bone marrow mononuclear cells (BMMCs) with EMP upregulated EPO expression. Furthermore, we found EPO and EPOR mRNAs as well as EPO protein in K562 cells, a human erythroleukemia cell line. Stimulation of K562 cells with EMP upregulated EPO expression. We suggest that EPO of erythroid origin may have a role in the regulation of erythropoiesis.

Human Hematopoietic Progenitors Express Erythropoietin

Erythropoietin (EPO) is a factor essential for erythroid cell proliferation, differentiation, and survival. The production of EPO by the kidneys in response to hypoxia and anemia is well documented. To determine whether EPO is also produced by hematopoietic cells, we analyzed the expression of EPO in normal human hematopoietic progenitors and in their progeny. Undifferentiated CD34+lin− hematopoietic progenitors do not have detectable EPO mRNA. Differentiating CD34+ cells that are stimulated with recombinant human EPO in serum-free liquid cultures express both EPO and EPO receptor (EPOR). Because CD34+ cells represent a heterogeneous cell population, we analyzed individual burst-forming units–erythroid (BFU-E) and nonerythroid colony-forming unit–granulocyte-macrophage colonies for EPO mRNA. Only BFU-E colonies were positive for EPO mRNA. Lysates from pooled BFU-E colonies stained positively for EPO by immunoblotting. To further confirm the intrinsic nature of erythroid EPO, we replaced extrinsic EPO in erythroid colony cultures with EPO-mimicking peptide (EMP). We show EPO expression in the EMP-stimulated BFU-Es at both mRNA and protein levels. Stimulation of bone marrow mononuclear cells (BMMCs) with EMP upregulated EPO expression. Furthermore, we found EPO and EPOR mRNAs as well as EPO protein in K562 cells, a human erythroleukemia cell line. Stimulation of K562 cells with EMP upregulated EPO expression. We suggest that EPO of erythroid origin may have a role in the regulation of erythropoiesis.

Fetal plasma iron and restoration of red blood cell mass after hemorrhage of the ovine fetus

OBJECTIVE

Our purpose was to determine whether the restoration of fetal red blood cell mass after acute hemorrhage of 40% of the fetal blood volume is related to fetal plasma iron concentration.

STUDY DESIGN

Ten chronically catheterized ovine fetuses were monitored for 10 days beginning at 125 +/- 1 (SE) days of gestation. After a 3-day control period 40% of the fetal blood was removed over 2 hours at a rate of approximately 1 ml/min. Fetal plasma iron and erythropoietin concentrations, hematocrit, blood volume, and red blood cell mass were measured daily before and for 7 days after fetal hemorrhage. Statistical analysis was by analysis of variance, correlation, and regression.

RESULTS

Although blood volume was restored within 3 days of the hemorrhage (101.0% +/- 1.4% of prehemorrhage volume), red blood cell mass was not (81.8% +/- 2.8%). Only 6 of 10 fetuses restored their red blood cell mass to prehemorrhage levels by the end of the 7-day posthemorrhage period. On day 10 red blood cell mass correlated positively with prehemorrhage (r = 0.74, p = 0.015) and posthemorrhage (r = 0.69, p = 0.045) plasma iron concentration and negatively with posthemorrhage erythropoietin concentration (r = -0.68, p = 0.047).

CONCLUSION

Fetal plasma iron concentration is an important factor in restoration of fetal red blood cell mass after loss of blood. The negative correlation of erythropoietin concentration with posthemorrhagic red blood cell mass suggests that iron, not erythropoietin, may be the limiting factor in recovery from hemorrhage-induced anemia. Thus iron supplementation of the fetus may be of benefit in the treatment of some types of fetal anemia.