Evaluation of the stability of human erythropoietin in samples for radioimmunoassay

One to one comparison of cell-free synthesized erythropoietin conjugates modified with linear polyglycerol and polyethylene glycol

With more than 20 Food and Drug Administration (FDA)-approved poly (ethylene glycol) (PEG) modified drugs on the market, PEG is the gold standard polymer in bioconjugation. The coupling improves stability, efficiency and can prolong blood circulation time of therapeutic proteins. Even though PEGylation is described as non-toxic and non-immunogenic, reports accumulate with data showing allergic reactions to PEG. Since PEG is not only applied in therapeutics, but can also be found in foods and cosmetics, anti-PEG-antibodies can occur even without a medical treatment. Hypersensitivity to PEG thereby can lead to a reduced drug efficiency, fast blood clearance and in rare cases anaphylactic reactions. Therefore, finding alternatives for PEG is crucial. In this study, we present linear polyglycerol (LPG) for bioconjugation as an alternative polymer to PEG. We report the conjugation of LPG and PEG by click-chemistry to the glycoprotein erythropoietin (EPO), synthesized in a eukaryotic cell-free protein synthesis system. Furthermore, the influence of the polymers on EPOs stability and activity on a growth hormone dependent cell-line was evaluated. The similar characteristics of both bioconjugates show that LPGylation can be a promising alternative to PEGylation.

Erythropoietin production by the kidney and the liver in response to severe hypoxia evaluated by Western blotting with deglycosylation

The detection of erythropoietin (Epo) protein by Western blotting has required pre‐purification of the sample. We developed a new Western blot method to detect plasma and urinary Epo using deglycosylation. Epo in urine and tissue, and erythropoiesis‐stimulating agents (ESAs) in urine were directly detected by our Western blotting. Plasma Epo and ESAs were not detected by direct application but were detected by our Western blotting after deglycosylation. The broad bands of Epo and ESAs were shifted to 22 kDa by deglycosylation except for PEG‐bound epoetin β pegol. The 22 kDa band from an anemic patient's urine was confirmed by Liquid Chromatography/Mass Spectrometry (LC/MS) to contain human Epo. Severe hypoxia (7% O_2, 4 hr) caused a 400‐fold increase in deglycosylated Epo expression in rat kidneys, which is consistent with the increases in both Epo gene expression and plasma Epo concentration. Immunohistochemistry showed Epo expression in nephrons but not in interstitial cells under control conditions, and hypoxia increased Epo expression in interstitial cells but not in tubules. These data show that intrinsic Epo and all ESAs can be detected by Western blot either directly in urine or after deglycosylation in blood, and that the kidney but not the liver is the main site of Epo production in control and severe hypoxia. Our method will make the tests for Epo doping and detection easy.

Intensive Predeposit-Hemodilution Autologous Blood Donation and IOBS Increase in Erythropoietic Levels in Patients Undergoing Hip Arthroplasty

Erythropoietin (EPO) plasma levels were monitored during the perioperative period in 61 consecutive patients (22 males - 39 females), aged 62.5 ± 9.5 years, scheduled for hip arthroplasty. All patients underwent intraoperative blood salvage (IOBS) and were subdivided into three different groups according to their hemoglobin levels (Hb) 24 hours postoperatively (group A: Hb < 8 g/dl; group B: Hb between 8-9 g/dl; group C: HB ≥ 9 g/dl). Seventy-two hours after surgery EPO levels were significantly different in group A (135 ± 68) compared to group C (54.3 ± 32), with a positive correlation (p < 0.01) between Hb and EPO levels. On the basis of these results we suggest that a programmed autologous red blood cell collection aimed at obtaining the lowest hemoglobin values during the first 24 hours after surgery, may be of clinical utility in preventing homologous blood needs.

Acute normobaric hyperoxia transiently attenuates plasma erythropoietin concentration in healthy males: evidence against the 'normobaric oxygen paradox' theory

AIM

The purpose of the present study was to evaluate the 'normobaric oxygen paradox' theory by investigating the effect of a 2-h normobaric O(2) exposure on the concentration of plasma erythropoietin (EPO).

METHODS

Ten healthy males were studied twice in a single-blinded counterbalanced crossover study protocol. On one occasion they breathed air (NOR) and on the other 100% normobaric O(2) (HYPER). Blood samples were collected Pre, Mid and Post exposure; and thereafter, 3, 5, 8, 24, 32, 48, 72 and 96 h, and 1 and 2 weeks after the exposure to determine EPO concentration.

RESULTS

The concentration of plasma erythropoietin increased markedly 8 and 32 h after the NOR exposure (approx. 58% and approx. 52%, respectively, P ≤ 0.05) as a consequence of its natural diurnal variation. Conversely, the O(2) breathing was followed by approx. 36% decrement of EPO 3 h after the exposure (P ≤ 0.05). Moreover, EPO concentration was significantly lower in HYPER than in the NOR condition 3, 5 and 8 h after the breathing intervention (P ≤ 0.05).

CONCLUSION

In contrast to the 'normobaric oxygen paradox' theory, the present results indicate that a short period of normobaric O(2) breathing does not increase the EPO concentration in aerobically fit healthy males. Increased O(2) tension suppresses the EPO concentration 3 and 5 h after the exposure; thereafter EPO seems to change in a manner consistent with natural diurnal variation.

Storage and preparation of samples for erythropoietin radioimmunoassay

The evaluation of a radioimmunoassay for erythropoietin developed using recombinant material as immunogen and radiotracer is presented. A series of serum samples prepared and stored under varying conditions showed that immunoreactive erythropoietin levels were stable at room temperature for at least 10 days and at -20 degrees C for 5 months. The optimum time for separating sera from samples was between 6 and 24 h after venepuncture. Serum EPO values were significantly higher than those measured in heparin or potassium EDTA plasma.

Erythropoietin in cerebrospinal fluid: age-related reference values and relevance in neurological disease

We aimed to establish age-related reference values for Erythropoietin (EPO) in cerebrospinal fluid (CSF) and to evaluate concentrations in neurological diseases. CSF and serum EPO was measured in controls with tension-type headache (CTTH), in patients with ALS, dementia and depression using ELISA technique. Stability experiments showed CSF EPO to be stable for two and a half months and over two thaw/freeze cycles. A positive correlation of CSF EPO with age was found (P<0.01). We found a CSF/serum EPO concentration ratio of 0.126, pointing towards an intrathecal synthesis of EPO. The ALS group showed significantly lowered CSF EPO compared to age-matched CTTH (P<0.012), whereas the dementia and depression group showed no significant differences compared to CTTH.The establishment of age-related reference values in a large cohort of controls will improve the interpretation of future CSF EPO evaluations in neurological diseases.

Pharmacokinetic-pharmacodynamic modelling of recombinant human erythropoietin in athletes : a population approach

OBJECTIVE

To develop a pharmacokinetic model able to take into account the negative feedback loop of endogenous erythropoietin production observed after repeated administration of recombinant human erythropoietin (rHuEPO), and to propose a pharmacokinetic-pharmacodynamic model capable of assessing and quantifying the relationship between changes in: (i) serum soluble transferrin receptor (sTfR) levels, (ii) reticulocyte haematocrit (RetHct), and (iii) percentage macrocytes (%Macro) secondary to repeated administration of rHuEPO.

SUBJECTS AND METHODS

Eighteen trained athletes (three females and 15 males) participated in this study. They received subcutaneous injections of rHuEPO-α 50 U/kg bodyweight for 26 days (days 1, 3, 5, 9, 10, 12, 15, 17, 19, 22, 24 and 26) with iron supplementation. Venous blood samples were collected before, during and after rHuEPO treatment for determination of serum erythropoietin concentrations, haematological parameters (RetHct, %Macro) and sTfR levels. Population pharmacokinetic-pharmacodynamic calculations were performed using NONMEM® software.

RESULTS

The serum erythropoietin concentration-time profile was compatible with a one-compartment open model and first-order input rate. The mean half-lives calculated from the first and the terminal log-linear parts of the curves were 5.2 and 35.8 hours, respectively. After subcutaneous administration of rHuEPO, the terminal part of the curve should correspond to the absorption rather than the elimination phase ('flip-flop' phenomenon). The total clearance divided by bio-availability was 4.33 L/h. The pharmacodynamic relationship based on a sigmoid E(max) model can be reasonably used to relate changes observed in haematological and biochemical markers after rHuEPO administration to changes in serum erythropoietin concentrations. rHuEPO induces a delayed increase in sTfR levels, RetHct and %Macro. The half-life (t1/2) k(0) (equilibration delay) values were 10.2 days for sTfR, 2 days for RetHct and 10.2 days for %Macro. The pharmaco-kinetic-pharmacodynamic approach developed in this study allowed below-base-line decreases in RetHct levels (i.e. from days 10-26 after the end of rHuEPO treatment) to be taken into account. A negative-feedback loop of red blood cell production further to high haemoglobin and haematocrit values could explain this decrease.

CONCLUSIONS

The approach described here may provide an additional tool in the war against drug abuse by athletes; indeed, the model could be useful for simulating pharmacokinetic-pharmacodynamic relationships according to different rHuEPO dosage schedules.

Amniotic fluid erythropoietin concentrations differentiate between acute and chronic causes of fetal death

BACKGROUND

Increased fetal plasma erythropoietin concentration is an indicator of chronic fetal hypoxia. Amniotic fluid erythropoietin levels correlate highly significantly with fetal erythropoietin levels before labor. We studied AF erythropoietin levels after fetal death in order to determine whether this could differentiate between stillbirths from acute or chronic causes.

METHODS

Amniotic fluid was obtained after fetal death for erythropoietin measurement following fetal death in 21 pregnancies. Two of the pregnancies had twins, of which one infant was born alive. All 22 stillborn fetuses had an autopsy. None had malformations. Without prior knowledge of the results of the erythropoietin analyzes, the causes of fetal death were divided into acute, chronic or unknown groups.

RESULTS

Eight pregnancies had an acute cause of fetal death (e.g. cord complication or placental abruption), eight pregnancies had a chronic cause (intrauterine growth restriction or erythroblastosis) and in five pregnancies the cause of fetal death could not be determined. In all eight pregnancies with an acute cause of fetal death, AF erythropoietin levels were normal (< 20 mU/mL). In contrast, six of the eight pregnancies with a chronic cause had AF erythropoietin levels above normal (range from 49.9 mU/mL to 391 mU/mL). In the five pregnancies with an unknown cause of fetal death, AF erythropoietin levels were normal in three and elevated in two.

CONCLUSIONS

Elevated AF erythropoietin levels, identified after fetal death, suggest that the fetus died from a chronic hypoxic event, whereas normal AF erythropoietin levels suggest that the fetus died from an acute event.

Effect of recombinant human erythropoietin on cerebral ischemia following experimental subarachnoid hemorrhage

Erythropoietin exerts a neuroprotective effect during cerebral ischemia. We investigated the effect of systemic administration of recombinant human erythropoietin in a rabbit model of subarachnoid hemorrhage-induced acute cerebral ischemia. The animals were divided into three groups: group 1, subarachnoid hemorrhage; group 2, subarachnoid hemorrhage plus placebo; group 3, subarachnoid hemorrhage plus recombinant human erythropoietin (each group, n=8). Experimental subarachnoid hemorrhage was produced by injecting autologous blood into the cisterna magna. Treatment with recombinant human erythropoietin and placebo was started 5 min after subarachnoid hemorrhage and was continued every 8 h for 24 h. Before the animals were killed, erythropoietin concentration was measured in the cerebrospinal fluid. The rabbits were killed 24 h after subarachnoid hemorrhage and ischemic brain injury was histologically evaluated. In group 3, the concentration of erythropoietin in the cerebrospinal fluid was significantly increased and a significant reduction in cortical necrotic neuron count was also observed. These findings may encourage the use of erythropoietin in the treatment of cerebral ischemia that often occurs in the early stage of subarachnoid hemorrhage.

Capillary/myocyte mismatch in the heart in renal failure--a role for erythropoietin?

BACKGROUND

Chronic renal failure is characterized by remodeling of the heart with left ventricular hypertrophy (increasing oxygen demand) and capillary deficit leading to capillary/myocyte mismatch (decreasing oxygen supply). Erythropoietin (Epo) has known angiogenic properties causing endothelial cell activation, migration and sprouting, mediated at least in part via the JAK/STAT (Janus kinase/signal transducers and activators of transcription) pathway. In uraemic cardiac hypertrophy the presence of diminished capillary supply implies that capillary growth does not keep pace with development of hypertrophy. To investigate whether this was due to a deficit of the angiogenic hormone Epo we examined whether Epo levels are altered and whether an increase in haematocrit by administration of rhEpo influences capillary supply, i.e. capillary/myocyte mismatch in experimental renal failure.

METHOD

Male Spraque-Dawley rats were either subjected to partial renal ablation or sham operation. Only modest amounts of renal tissue were removed so that the rats were not anemic. Subgroups of rats received either human (rh)Epo alone or in combination with unspecific antihypertensive treatment (dihydralazine plus furosemide) in order to control the Epo induced rise in blood pressure. Capillary supply was measured stereologically as capillary length per volume myocardium using the orientator method.

RESULTS

Capillary length density was reduced by approximately 25% after partial renal ablation (3237+/-601 vs 4293+/-501 mm/mm(3) in controls). It was not statistically different in animals with partial renal ablation+rhEpo+antihypertensive treatment (3620+/-828 mm/mm(3)) compared to partial ablation alone.

CONCLUSION

The study shows that lack of Epo does not cause, or contribute to, the deficit of capillary growth in the hypertrophied left ventricle of rats with renal failure. In addition, a rise in haematocrit is not accompanied by beneficial effects on alterations of cardiovascular structure in experimental renal failure.

Important role of nondiagnostic blood loss and blunted erythropoietic response in the anemia of medical intensive care patients

OBJECTIVE

To determine incidence, severity, characteristics, and causes of anemia and transfusion requirements in medical intensive care patients.

DESIGN AND SETTING

Open prospective clinical study in a 24-bed medical intensive care unit in a tertiary-care university hospital.

PATIENTS

Patients (N = 96) treated in the intensive care unit for >3 days.

INTERVENTIONS

None.

MEASUREMENTS

Parameters of erythropoiesis and red blood cell metabolism, including hemoglobin, reticulocyte counts, serum iron, transferrin, ferritin, haptoglobin, vitamin B12, folic acid, and erythropoietin concentrations were determined serially. Diagnostic blood loss and red blood cell transfusions were recorded, and the total blood loss was estimated from changes in hemoglobin concentrations and the amount of hemoglobin transfused.

MAIN RESULTS

The median hemoglobin concentration was 12.1 g/dL at admission and 11.2 g/dL at the end of the intensive care unit stay. A total of 74 patients (77%) suffered from anemia and received 257 red blood cell units, approximately half of which were given within the first 5 days. Three patients who received 19 red blood cell units were admitted with acute gastrointestinal bleeding, but in the remainder, a median total blood loss of 128 mL/d was not (n = 60) or not solely (n = 11) a result of overt bleeding. Diagnostic blood loss declined from a median of 41 mL on day 1 to <20 mL after 3 wks and contributed 17% (median) to total blood loss. Acute renal failure, fatal outcome, and simplified acute physiology score >38 on admission were associated with a 5.8-, 7.0-, and 2.8-fold increase in total blood loss. Reticulocyte counts and erythropoietin concentrations were inappropriately low for the degree of anemia, and plasma transferrin saturation was mostly <20%.

CONCLUSIONS

Anemia is frequent and results in a high requirement for red blood cell transfusions in the medical intensive care setting. A major proportion of blood loss is not caused by overt bleeding or diagnostic blood sampling but, rather, may result from various other reasons, e.g., occult gastrointestinal bleeding and renal replacement therapy. The erythropoietic response to anemia is blunted, probably as a consequence of an inappropriate increase in erythropoietin production and diminished iron availability. (Crit Care Med 1999; 27:2630-2639)

Effects of erythropoietin administration in training athletes and possible indirect detection in doping control

PURPOSE

This study investigated the effects of repeated subcutaneous injection of rHuEpo (50 IU x kg(-1)) in athletes and proposes a method based on the measurement in blood samples of the sTfR/serum protein ratio to determine if the observed values of this marker are related to rHuEpo abuse.

METHODS

Serum erythropoietin concentrations, and hematological and biochemical parameters were evaluated, during treatment and for 25 d posttreatment in nine training athletes. Moreover, the effect of rHuEpo administrations on the maximum oxygen uptake (VO2max) and ventilatory threshold (VT) of these athletes was also studied. Threshold values for sTfr and the sTfr/serum protein ratio were determined from 233 subjects (185 athletes, 15 athletes training at moderately high altitude, and 33 subjects living at >3000 m).

RESULTS

Significant changes in reticulocytes, hemoglobin (Hb) concentration, hematocrit (Hct), sTfr, and sTfr/serum proteins were observed during and after rHuEpo treatment. The maximal heart rate of 177 beats x min(-1) at the beginning of the study was significantly higher than the value of 168 beats x min(-1) after 26 d of rHuEpo administration. Compared with the values measured at baseline, the VT measured after rHuEpo administration occurred at a statistically significant high level of oxygen uptake.

CONCLUSIONS

When oxygen uptake measured at the VT was expressed as a percentage of V02 max, the values obtained were also significantly higher. The increased values of Tfr and sTfr/serum proteins, respectively, above 10 microg x mL(-1) and 153, indicated the probable intake of rHuEpo.

Are current methods of measurement of erythropoietin (EPO) in human plasma or serum adequate for the diagnosis of polycythaemia vera and the assessment of EPO deficiency?

Current methodology for the immunoassay of erythropoietin (EPO) in human plasma or serum is reviewed, with an emphasis on measurement of EPO concentrations in the low and normal ranges, analytical interference and blood sampling requirements. In only 2 out of 8 research or in-house immunoassays reported since 1987 was there evidence that patients with polycythaemia vera (PV) could be identified, PV being an EPO-independent form of polycythaemia in which EPO concentrations are low in untreated cases. The same was true for only 1 out of 13 currently available kit methods. Remarkable differences in sample stability have been observed with different methods. Measurement of EPO in serum is recommended in most published articles. However, only EDTA plasma seems to be acceptable for the one generally available method with proven high diagnostic sensitivity for PV. It is concluded that most EPO assay methods have not been shown to be adequate for the measurement of the low EPO concentrations, and thus have poor diagnostic sensitivity for PV. It is inferred that they might not be appropriate to assess states of EPO deficiency. Only when a sufficiently sensitive diagnostic method becomes generally available will it be possible to define the various causes of low EPO concentrations. As in other fields of polypeptide hormone measurement, further developments in the field of EPO assay may be expected to be important in diagnostic medicine.

Fetuses from preeclamptic mothers show reduced hepatic erythropoiesis

The fetal liver is the main hematopoietic organ during intrauterine life. Morphometrical studies were performed on liver sections to detect changes occurring with intrauterine growth retardation and preeclampsia. Compared with the controls (n = 10), fetuses from preeclamptic mothers showed a severe reduction of erythroid cells by 60% on average (n = 18). Closer examination revealed that the erythroid cells at early stages of differentiation were more affected (80% reduction) than at later stages (55%). Seven out of 18 fetuses from preeclamptic mothers did not show growth retardation but exhibited severely reduced hepatic erythropoiesis. We suggest that the prime factor for impaired red blood cell production is preeclampsia itself rather than intrauterine growth retardation. Regulation of erythropoiesis in utero might depend on the interaction of many hematopoietic growth factors, and preeclampsia might alter the balance. To test this notion, we quantitated erythropoietin in fetal blood and various cytokines in the amniotic fluid. An elevation of erythropoietin and interleukin (IL)-3 levels was seen in babies born under the conditions of preeclampsia, whereas the concentrations of granulocyte/macrophage-colony-stimulating factor (CSF), granulocyte-CSF, and IL-1 beta were reduced, and the levels of IL-6 and IL-8 remained constant. With preeclampsia, a discrepancy between elevation of erythrocyte numbers in peripheral blood and depression of hematopoiesis at the main production site, the fetal liver, is seen. Concomitantly, there is elevation of some but reduction of other hematopoietic cytokines. We envision that during the course of preeclampsia quantitation of hematopoietic growth factors might allow to predict the deterioration of in utero life conditions.

Evidence against a major role of adenosine in oxygen-dependent regulation of erythropoietin in rats

This in vivo study investigated whether adenosine (ADO) plays a role in oxygen-dependent production of erythropoietin (EPO). Exposure of rats to 0.075% carbon monoxide (CO) for four hours was used as a stimulus for EPO production. To inhibit potential effects of ADO, rats were treated with the non-specific ADO antagonist theophylline, the selective ADO A1 receptor blockers DPCPX and KW-3902, the selective ADO A2 receptor blocker DMPX, and AOPCP, an inhibitor of 5'-ectonucleotidase, an ADO generating enzyme that is expressed on the surface of EPO producing cells. To stimulate ADO receptor activity, animals were treated with the selective ADO A1 and A2 receptor agonists CHA and CGS 21680, the ADO reuptake inhibitors dipyridamole and soluflazine and the ADO desaminase inhibitor EHNA. At doses known to interfere with ADO signal transmission in vivo, none of these substances either influenced EPO serum levels in normoxic rats or affected the approximately 30-fold rise in EPO serum levels and the increase in renal EPO mRNA after exposure to carbon monoxide. Continuous administration of theophylline to normoxic rats for seven days did not alter hematocrit, hemoglobin or EPO serum levels. Taken together, these experiments do not support the hypothesis that ADO plays an important role in the regulation of EPO production.

Detection of erythropoietin in human liquor: intrinsic erythropoietin production in the brain

Until now, erythropoietin (EPO) was thought to be produced exclusively in fetal liver and adult kidney and to regulate mammalian erythropoiesis. However, we recently showed that steady state levels of EPO mRNA could be induced up to 100-fold in primary mouse astrocytes cultured under hypoxic conditions, and also reported the presence of mRNA for EPO and its receptor in the brain of mouse, monkey and human. In extending these studies on humans we now show that immunoreactive EPO is present in ventricular cerebrospinal fluid (CSF) of 5 patients with traumatic brain injuries: EPO was found in 15 out of 15 CSF samples. There was no correlation between the serum EPO concentration and the concentration in the CSF. However, EPO concentrations in CSF correlated with the degree of blood-brain-barrier dysfunction. This suggests that EPO does not cross the intact blood-brain-barrier, implying that EPO is produced in the brain itself, most probably by astrocytes in an oxygen-dependent manner. In view that neuronal cells carry the EPO receptor, we propose that EPO acts in a paracrine fashion in the central nervous system and might function as a protective factor against hypoxia-induced damage of neurons.

Erythropoietin production in rats with post-ischemic acute renal failure

To study the role of erythropoietin (Epo) in the pathogenesis of anemia in acute renal failure (ARF), organ Epo mRNA was measured by RNase protection assay in rats with ARF induced by a one hour-occlusion of the left renal artery. Hematocrit was significantly decreased two hours, 24 hours and one week after renal artery occlusion. A significant reduction in serum haptoglobin at two hours and an increase in serum LDH at 24 hours indicated that hemolysis was the likely cause of the initial fall in hematocrit. However, despite the reduced hematocrit, serum Epo concentrations were not significantly different from controls, suggesting that the anemia is maintained because of lack of an appropriate Epo response. Right renal Epo mRNA levels were not significantly different in all groups, but Epo mRNA levels in post-ischemic kidneys were 50 to 67% lower than in contralateral kidneys. However, Epo mRNA in the post-ischemic kidney was increased sixfold by acute hemorrhage, a rise comparable to the ninefold increase observed in contralateral kidneys. In ARF rats exposed to 7.5% O2 for four hours, right kidney Epo mRNA increased 200-fold over normoxic levels, to a value similar to sham-operated hypoxic controls. Epo mRNA in the post-ischemic kidney also increased 200-fold, to 50% of the level in the contralateral kidney. Hepatic Epo mRNA levels were elevated to comparable levels in both groups. In this ARF model, mild anemia is associated with relative Epo deficiency. In the post-ischemic kidney, a substantial capacity for Epo production is retained but the sensitivity of the Epo response to blood oxygen availability is significantly reduced.

Erythropoietin gene expression in human, monkey and murine brain

The haematopoietic growth factor erythropoietin is the primary regulator of mammalian erythropoiesis and is produced by the kidney and the liver in an oxygen-dependent manner. We and others have recently demonstrated erythropoietin gene expression in the rodent brain. In this work, we show that cerebral erythropoietin gene expression is not restricted to rodents but occurs also in the primate brain. Erythropoietin mRNA was detected in biopsies from the human hippocampus, amygdala and temporal cortex and in various brain areas of the monkey Macaca mulatta. Exposure to a low level of oxygen led to elevated erythropoietin mRNA levels in the monkey brain, as did anaemia in the mouse brain. In addition, erythropoietin receptor mRNA was detected in all brain biopsies tested from man, monkey and mouse. Analysis of primary cerebral cells isolated from newborn mice revealed that astrocytes, but not microglia cells, expressed erythropoietin. When incubated at 1% oxygen, astrocytes showed >100-fold time-dependent erythropoietin mRNA accumulation, as measured with the quantitative reverse transcription-polymerase chain reaction. The specificity of hypoxic gene induction in these cells was confirmed by quantitative Northern blot analysis showing hypoxic up-regulation of mRNA encoding the vascular endothelial growth factor, but not of other genes. These findings demonstrate that erythropoietin and its receptor are expressed in the brain of primates as they are in rodents, and that, at least in mice, primary astrocytes are a source of cerebral erythropoietin expression which can be up-regulated by reduced oxygenation.

Hypoxia, a novel inducer of acute phase gene expression in a human hepatoma cell line

Transcriptional regulation of gene expression by hypoxia is an important, but yet only marginally characterized mechanism by which organisms adapt to low oxygen concentrations. The human hepatoma cell line HepG2 is a widely used model for studying hypoxic induction of the hematopoietic growth factor erythropoietin. In an attempt to identify additional genes expressed in HepG2 cells during hypoxia, we differentially screened a cDNA library derived from hypoxic (1% O2) HepG2 cells using probes isolated from either normoxic (21% O2) or hypoxic cells. Two genes were identified, one encoding aldolase, a member of the glycolytic enzymes, and the other encoding alpha 1-antitrypsin which belongs to the family of the acute phase (AP) responsive proteins. Whereas hypoxic induction of glycolytic enzymes is well established, oxygen-dependent regulation of AP genes has not been reported so far. AP proteins are liver-derived plasma proteins whose production during inflammation is either up-regulated (positive AP reactants) or down-regulated (negative AP reactants). In the present study, we demonstrate that on the mRNA level hypoxic stimulation of HepG2 cells led to (i) an induction of the positive AP reactants alpha 1-antitrypsin, alpha 1-antichymotrypsin, complement C3, haptoglobin, and alpha 1-acid glycoprotein; (ii) a down-regulation of the negative AP reactant albumin; (iii) an up-regulation of the negative AP reactant transferrin; and (iv) unchanged levels of the positive AP reactants alpha- and beta-fibrinogen as well as hemopexin. Cycloheximide inhibited hypoxic up-regulation of AP mRNAs demonstrating that de novo protein synthesis is required for hypoxic induction. Nuclear run-on assays indicate that the hypoxic increase in AP mRNAs is mainly due to transcriptional regulation. The hypoxic response was compared to AP stimulation by interleukin 6. The results suggest that the adaptive response to hypoxia overlaps with, but is not identical with, the AP response mediated by interleukin 6.

Modulation of erythropoietin formation by changes in blood volume in conscious dogs

1. A possible influence of the filling of the circulatory system on the plasma concentration of erythropoietin, which is the major regulator of erythrocyte formation, was investigated in conscious dogs. 2. Over an experimental period of 5 h, the animals were subjected to either haemorrhage (hypovolaemia), blood volume expansion (hypervolaemia), or exchange transfusion of blood with dextran (isovolaemic anaemia). 3. A reduction of blood volume by 20% induced by haemorrhage increased plasma erythropoietin levels approximately 1.5-fold in the absence of significant changes in haematocrit. 4. An expansion of blood volume by 12% induced by an intravenous infusion of dextran did not change plasma erythropoietin levels, although the haematocrit decreased by 0.04. 5. A reduction of the haematocrit by 0.12 in the absence of changes in blood volume induced by an isovolaemic exchange transfusion (dextran vs. blood) increased plasma erythropoietin levels approximately 3-fold. 6. Total renal oxygen supply did not change in any of the three experimental protocols. 7. These data indicate that in dogs the erythropoietin production rate is modulated by changes in blood volume, and suggest a possible role of erythropoietin in the regulation of blood volume.

Localization of specific erythropoietin binding sites in defined areas of the mouse brain

The main physiological regulator of erythropoiesis is the hematopoietic growth factor erythropoietin (EPO), which is induced in response to hypoxia. Binding of EPO to the EPO receptor (EPO-R), a member of the cytokine receptor superfamily, controls the terminal maturation of red blood cells. So far, EPO has been reported to act mainly on erythroid precursor cells. However, we have detected mRNA encoding both EPO and EPO-R in mouse brain by reverse transcription-PCR. Exposure to 0.1% carbon monoxide, a procedure that causes functional anemia, resulted in a 20-fold increase of EPO mRNA in mouse brain as quantified by competitive reverse transcription-PCR, whereas the EPO-R mRNA level was not influenced by hypoxia. Binding studies on mouse brain sections revealed defined binding sites for radioiodinated EPO in distinct brain areas. The specificity of EPO binding was assessed by homologous competition with an excess of unlabeled EPO and by using two monoclonal antibodies against human EPO, one inhibitory and the other noninhibitory for binding of EPO to EPO-R. Major EPO binding sites were observed in the hippocampus, capsula interna, cortex, and midbrain areas. Functional expression of the EPO-R and hypoxic upregulation of EPO suggest a role of EPO in the brain.

Lack of permeability of the human placenta for erythropoietin

Measurements of erythropoietin in fetal blood obtained by cordocentesis or in umbilical cordblood and maternal blood have shown a lack of correlation indicating an independent regulation of EPO concentration in fetal and maternal compartments. There is a good correlation between amniotic fluid EPO concentration in fetal blood levels. Fetal EPO concentration therefore might serve as an indicator of chronic fetal hypoxia with fetal EPO production being responsive to tissue hypoxia early on in pregnancy. The lack of human placental permeability for EPO was further investigated using a dual in vitro perfusion system of an isolated cotyledon in freshly delivered term placentae. With recirculation of both circuits trace amounts of EPO (0.04% of the amount added to the maternal compartment) were transferred to the fetal side during 4-5 hours of perfusion. This transfer is comparable to the rate determined in the same experiments for albumine, and the biological significance of this very slow transfer is questionable. A very low rate of diffusion across the human placenta has also been shown for dextran, horseradish peroxidase and heparin using an in vitro perfusion system. The only exception among macromolecules are immunoglobulines G, which towards the end of pregnancy are transferred by an Fc-receptor mediated transcellular mechanism from the mother to the fetus. It is concluded, that there is no easy exchange of EPO across the human placenta between maternal and fetal compartments. Changes in EPO concentration in the fetal compartment therefore could serve as indicator of fetal hypoxia. A therapeutic application of EPO in the mother for the treatment of chronic anemia would not have any effect on fetal tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythropoiesis in the postpartum period

The puerperium is a time of immense physiological changes for the female organism. Erythropoiesis plays one of the central roles in these processes. The aim of this investigation was to describe physiological erythropoiesis in healthy women during the puerperium. Blood samples were taken just before delivery and on days 1, 2, 3, 4 and 14 postpartum. In addition to the usual parameters such as hemoglobin, hematocrit, platelets, leucocytes, ferritin, CRP, endogenous erythropoietin, etc., the absolute and the percentage reticulocyte counts-both the total and for the subpopulations-were determined by flow cytometry. The mean Hb values decreased in the first 24 hours postpartum by 0.8 g/dl and then rose to 0.2 g/dl more than the initial value on day 14. The reticulocytes reflected erythropoietic stimulation with an increase from day 0 to day 1 of 2.1% (79.1 x 10(9)/1) and a continual decrease thereafter. The hematological parameters followed a characteristic course in the puerperium. For the reticulocytes and the subpopulations, a definite erythropoietic stimulation was evident even before delivery, as was an increase in the erythropoietic activity in the early puerperium.

Pharmacokinetics of recombinant human erythropoietin in children treated with continuous ambulatory peritoneal dialysis

In children treated by continuous ambulatory peritoneal dialysis (CAPD) renal anaemia is preferably treated by intraperitoneal administration of erythropoietin, since subcutaneous administration is painful and frightening for the child. Pharmacokinetics of erythropoietin were studied in three groups of children treated by CAPD. In group subcutaneous (SC) (n = 5) erythropoietin was administered subcutaneously, whereas in group intraperitoneal 1 (IP1) (n = 8) and intraperitoneal 2 (IP2) (n = 8) erythropoietin was given intraperitoneally during a 12-h dwell. Group IP1 received erythropoietin in 20 ml/kg of dialysis fluid, while in group IP2 the hormone was added to only 50 ml of dialysate, irrespective of body weight. The median area under the curve (AUC) was 4064 mU.h/ml (range 2647-24357) in group SC, 1698 (570-5514) in group IP1 and 3577 (1225-6555) in group IP2. In comparison to group SC the AUC was significantly lower in group IP1 (Wilcoxon: P = 0.02). The difference between group SC and group IP2 was not statistically significant.

CONCLUSION

In children on CAPD the resorption of erythropoietin after intraperitoneal administration, measured as AUC, is similar to subcutaneous administration, when erythropoietin is administered in 50 ml of dialysate. The dose needed to treat renal anaemia with erythropoietin administered intraperitoneally this way will have to be established in a therapeutic study.

Characterization of the Han:SPRD rat model for hereditary polycystic kidney disease

The Han:SPRD rat model for inherited polycystic kidney disease (PKD) was characterized (clinical parameters, morphology, immunohistochemistry and in situ hybridization). Homozygous animals died of uremia after three to four weeks with severe cystic transformation of virtually all nephrons and collecting ducts (serum urea: 616 +/- 195 mg/dl; kidney-to-body weight ratio: > 20%). In heterozygotes, slow progression of the disease led to death between the 12th and 21st month (median: 17 months; serum urea levels above 200 mg/dl). Kidney enlargement was moderate, and cysts were restricted to the cortex and outer medulla. Immunohistochemical markers showed that approximately 75% of the cysts were derived from the proximal tubule. Cystic transformation started in the proximal tubule with a sharp onset of basement membrane alteration and a loss of epithelial differentiation restricted to small focal areas. In these areas, alpha 1(IV) collagen and laminin B1 mRNA were enhanced as revealed by isotopic and non-isotopic in situ hybridization. Fibroblasts underlying the affected tubular portions were involved in matrix overexpression resulting in subepithelial accumulation of immunoreactive collagen IV and laminin. In later stages of cystic transformation distal nephron segments were affected as well. A reversal in epithelial polarity as judged from Na,K-ATPase-immunoreactivity was not observed. Renal immunoreactive renin-status was significantly decreased. Hematocrit was lowered in heterozygotes (40.4 +/- 5.8 vol% compared to 46.7 +/- 1.99 vol% in controls; P < 0.05) and total renal EPO mRNA was reduced to 36 +/- 14% of the mean value of control animals, whereas serum EPO levels were not significantly altered. We conclude that the Han:SPRD rat is a useful model for the study of human ADPKD since both diseases are similar in several aspects. The model is particularly suitable for the study of epithelial-mesenchymal interactions at the beginning of tubular cystic transformation.

rh-erythropoietin stimulates immature reticulocyte release in man

The pharmacodynamics of single intravenous dosing with recombinant human erthropoietin (rhEPO) was investigated in eight healthy volunteers (150 U/kg, n = 2; 300 U/kg, n = 6) with respect to reticulocyte subdivisions (by fluorescence flow cytometry) and serum ferritin over 6.5 d. The present study shows that bolus rhEPO injection produces an immediate release of high and middle fluorescence (immature) reticulocytes with a high RNA content from the marrow into the circulation, whereas the low fluorescence (more mature) reticulocytes were at first not affected. Serum ferritin decreased markedly within 24 h, reaching a nadir 50% of baseline after 120 h (5 d), with no increase in haemoglobin. Our data suggests that rhEPO triggers premature expulsion of immature reticulocytes from the bone marrow into the circulation independent of its effect in stimulating erythropoiesis and that rhEPO has an effect on serum ferritin concentration which in this dynamic situation is dependent not only on the iron stores.

Lack of transport of erythropoietin across the human placenta as studied by an in vitro perfusion system

The transfer of human recombinant erythropoietin (rhEPO) from the maternal to the fetal side was investigated using the technique of in vitro perfusion of an isolated cotyledon of human placenta, with recirculation of the perfusate (130 ml) in separate closed maternal and fetal circuits. rhEPO (221-512 U), together with [14C]BSA (bovine serum albumin, 44.8 kBq or 2,688,000 dpm), was added to the maternal circuit only. Despite a considerably lower molecular weight of EPO (mol. wt. = 30,400 Da) compared to BSA (mol. wt. = 69,000 Da), no difference was found in their transfer across the placenta from the maternal to the fetal side, which was very low for both macromolecules. The total transfer of rhEPO derived from the concentration measured in the samples taken from the fetal circuit at the end of 4-5 h of perfusion, was in the range of 0.04% of the amount initially added to the maternal compartment. A similar amount of transfer was determined for [14C]BSA (0.04-0.07%, n = 12). In conclusion, by direct determination in a dually in vitro perfused human placental cotyledon, no significant transfer of rhEPO from the maternal to the fetal side could be shown.

Perioperative plasma erythropoietin levels in hip arthroplasty

To examine the influence of intra- and postoperative blood loss and operative trauma on erythropoietin (EPO) production we studied patients undergoing endoprosthetic surgery of the hip. Immunoreactive plasma EPO was determined in ten patients (seven male, three female, aged 39-68 years), undergoing surgery for hip arthroplasty (n = 8) or revision hip arthroplasty (n = 2). EPO levels had already been determined during preoperative autologous deposit, thus allowing direct comparison between EPO response to blood loss alone and the response to blood loss and operative trauma. Perioperative blood loss amounted to 1720 (480-8100) ml (median, range). The hemoglobin concentration decreased from 12.4 (10.6-14.0) g/dl (median, range) before the operation to 10.0 (9.3-12.3) g/dl 2 h after the operation. Thereafter, the hemoglobin concentration increased slowly due to transfusion and erythropoiesis and was not significantly different (p < 0.05) from the preoperative value on the seventh postoperative day. The EPO concentration was preoperatively 26 (11-28) mU/ml and increased 2 h after the end of the operation, reaching a peak of 64 (45-104) mU/ml at 24 h. This peak was followed by a plateau at lower, but still elevated levels. The EPO concentration remained significantly elevated above the preoperative value on the seventh postoperative day. Plasma EPO concentrations showed an adequate response to postoperative anemia compared with the time course after autologous donation. In the early postoperative phase, they do not seem to be appreciably influenced by the neuroendocrine response to trauma, by mediators of inflammation, or by the postoperative catabolic state. The slightly elevated EPO concentration in the late postoperative phase indicates that factors other than anemia may contribute to EPO production at this time.

Serum erythropoietin levels in patients with solid tumours

Patients with malignant disease frequently develop anaemia. To investigate the role of erythropoietin (EPO) in this anaemia, serum levels were determined in patients with solid tumours. The study population consisted of 84 patients (44 males, 40 females) with solid tumours and 99 healthy control subjects, and 13/84 patients were anaemic. Serum EPO was clearly elevated in the anaemic tumour patients, but this increase was less than in patients suffering from iron deficiency anaemia. As in iron deficiency anaemia, the correlation between EPO levels and haemoglobin values was inverse. When compared to healthy control subjects, the levels of EPO in the tumour patients without anaemia were decreased. We conclude that there may be an inhibition in the expression or secretion of EPO in patients with solid tumours which, as yet, has not been further defined. Based on this, the treatment of anaemia in cancer patients with erythropoietin appears promising.

Oxygen-dependent expression of the erythropoietin gene in rat hepatocytes in vitro

Since in juvenile rats the liver is the predominant site of erythropoietin (EPO) gene expression, we have used primary cultures of juvenile rat hepatocytes to establish and in vitro system for investigation of oxygen-dependent EPO formation. When isolated hepatocytes were incubated at reduced oxygen tensions for 18-48 h, we found increased secretion of EPO protein and elevated levels of EPO mRNA, as determined by RNas protection. This increase was maximal at 3% O2, where EPO mRNA levels after 18 h were approximately 15-fold higher than at 20% O2. The increase in EPO mRNA at low oxygen tensions was specific insofar as [3H]uridine incorporation, as a measure of total RNA synthesis, was reduced by approximately 50% at 3% O2, and it appeared to involve gene transcription since it was abolished in the presence of actinomycin D (35 microM). Significant increases in EPO mRNA were also observed in cells kept at 20% oxygen in the presence of cobalt chloride (50 microM) and nickel chloride (400 microM), but EPO mRNA levels achieved under these conditions were less than 7% of those in cells incubated at 3% oxygen. No increase in EPO mRNA levels was observed in cultures incubated at 20% O2 in the presence of cyclic dibutyryl-AMP (10 microM-3 mM), cyclic 8-bromoGMP (10 microM-1 mM), cyclohexyladenosine (1 microM), 5'-N-ethylcarboxamidoadenosine (1 microM) and phorbol 12-myristate 13-acetate (3 nM). In the presence of 10% carbon monoxide, used to block haem proteins in their oxy conformation, EPO mRNA levels in hepatocytes incubated at low oxygen tensions were reduced to 63%.(ABSTRACT TRUNCATED AT 250 WORDS)

End-stage kidneys are capable of increased erythropoietin production

A relative deficiency of erythropoietin (EPO) is the most important factor responsible for the anaemia of end-stage renal failure. Patients on continuous ambulatory peritoneal dialysis usually maintain a higher haemoglobin concentration than patients on other forms of dialysis. The precise mechanism is uncertain, and there is disagreement over the role of increased EPO production. An 11-year-old boy with end-stage renal failure maintained on overnight cycling peritoneal dialysis developed a reticulocytosis, followed by a marked increase in haemoglobin concentration, shortly after his dialysis schedule was altered to include a full peritoneal cavity during the daytime. This improvement in erythropoiesis was closely associated with an increase in serum EPO concentration. We suggest that the alteration in dialysis may have resulted in enhanced clearance of an inhibitor of EPO production and discuss the possible mechanisms involved.

Lack of associations between fetal and maternal serum-erythropoietin at birth

Erythropoietin (EPO) is known to be the main regulator of erythropoiesis. We wanted to determine whether EPO production during pregnancy takes place independently in the mother and the fetus, and to identify the factors which set the EPO level. Endogenous EPO levels were determined in simultaneous samples from the umbilical vein, the umbilical artery and a maternal vein in 126 mother-child pairs and simultaneously from amniotic fluid (n = 14) in unselected births. Results were related to clinical and biochemical parameters of fetal well-being, mode of delivery, duration of labor, and infant parameters at birth. There was a weak correlation between maternal and fetal log EPO values (umbilical vein: r2 = 0.11; umbilical artery: r2 = 0.08), but a highly significant correlation between log EPO levels in the two umbilical vessels (r2 = 0.91) and between both umbilical blood and amniotic fluid (r2 = 0.41). Maternal EPO levels were lower than fetal levels in 76 cases, higher in 47, and nearly identical in 3. Increased fetal EPO levels were associated with clinical and biochemical indicators of fetal stress. These associations help to explain why EPO concentrations in fetal blood are independent of maternal levels and also indicate that EPO does not cross the placental barrier. These findings are discussed in the light of the animal experimental and in vitro evidence for placental transfer of EPO. Our data, and the work of others, make such a transfer in humans quite unlikely. This observation has therapeutical consequences for the treatment of maternal anemia with recombinant human EPO.

Distribution of erythropoietin producing cells in rat kidneys during hypoxic hypoxia

We have used in situ hybridization to determine the localization and distribution of cells expressing the erythropoietin (EPO) gene in kidneys of rats exposed to reduced oxygen tensions to characterize the control of renal EPO formation during hypoxic hypoxia. Animals were subjected to severe hypoxia (7.5% O2) for 4, 8 and 32 hours to assess changes related to the duration of hypoxic exposure, and additionally to 9% and 11.5% O2 for eight hours to define changes related to the degree of hypoxia. The number of cells containing EPO mRNA were counted on tissue sections and compared to tissue concentrations of EPO mRNA and to the serum hormone concentrations. In situ hybridization revealed expression of the EPO gene exclusively in peritubular cells that were predominantly located in the cortical labyrinth under all conditions tested. After four hours of severe hypoxia (7.5% O2) approximately 170-fold more cells were found to contain EPO mRNA than under normoxic conditions. The number of EPO producing cells did not change significantly between four and eight hours exposure to 7.5% O2, but the amount of EPO mRNA per kidney increased approximately threefold. Further continuation of hypoxia resulted in down-regulation of renal EPO mRNA levels, which was mainly due to a reduction in the number of cells containing EPO mRNA. Comparison of graded degrees of hypoxia applied for eight hours showed an inverse exponential relationship between oxygen tension and the number of EPO producing cells. This recruitment of cells expressing the EPO gene occurred along a gradient extending from the corticomedullary border to the subcapsular tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythropoietin treatment for chronic anemia of selected hematological malignancies and solid tumors

BACKGROUND

Neoplasias, especially in their more advanced stages, are often associated with chronic anemia of malignancy which impairs the patient's physical ability and quality of life.

PATIENTS AND METHODS

Forty-two patients with chronic anemia associated with hematological malignancies (18 multiple myelomas, 10 myelodysplastic syndromes) or solid tumors (9 breast cancers, 5 colon cancers) were treated with 150-300 units/kg rHuEPO for a median time period of 16 weeks. Response was defined as an increase of the initial hemoglobin level by at least 2 g/dl.

RESULTS

The response rates for solid tumors were comparable (44.4% and 40% for breast cancer and colon cancer, respectively), whilst the response in patients with hematological malignancies depended strongly on the disease entity (77.8% for multiple myeloma, 10% for myelodysplastic syndrome). Pretreatment serum levels of endogenous erythropoietin (EPO) were significantly higher in non-responding patients than in responders. During rHuEPO therapy, EPO levels in non-responders increased even further, while they remained basically unchanged in responding patients. In responders, the WHO performance status before the start of rHuEPO therapy was more favorable and showed impressive improvement during the course of treatment. The median survival time of responders was 28.0 months as compared to only 9.2 months for non-responders. Clinical symptoms of anemia subsided or at least considerably improved under successful rHuEPO therapy. With the exception of occasional flu-like symptoms, no undesirable effects of rHuEPO treatment were observed.

CONCLUSIONS

In conclusion, rHuEPO treatment corrected anemia of malignancy both in patients with hematologic disease and in those with solid tumors, but responsiveness varied considerably amongst the different disease entities.

Pharmacokinetics of recombinant human erythropoietin applied subcutaneously to children with chronic renal failure

The single-dose pharmacokinetics of recombinant human erythropoietin (rHuEPO) given SC was investigated in 20 patients aged 7-20 years at different stages of chronic renal failure. In a pilot study we confirmed the lower bioavailability of the drug in 2 children when given SC compared with the IV route (24% and 43%, respectively). Following administration of 4,000 units/m2, rHuEPO SC effective serum erythropoietin concentrations increased from a mean baseline level (+/- SD) of 23 +/- 13 units/l to a mean peak concentration of 265 +/- 123 units/l, which was reached after 14.3 +/- 9.4 h, followed by a slow decline until baseline values were attained at 72 h. Mean residence time was 30 +/- 9 h and mean elimination half-time 14.3 +/- 7 h. The single-dose kinetics of SC rHuEPO in children with different degrees of renal failure are comparable to those in adult patients. Possibly, the higher efficacy of SC rHuEPO in patients with renal anaemia compared with IV rHuEPO is related to its prolonged action.

Increased plasma viscosity as a reason for inappropriate erythropoietin formation

The aim of this study was to examine whether altered plasma viscosity could contribute to the inappropriately low production rate of erythropoietin (EPO) observed in patients suffering from hypergammaglobulinemias associated with multiple myeloma or Waldenström's disease. We found that the EPO formation in response to anemia in these patients was inversely related to plasma viscosity. A similar inverse relationship between plasma viscosity and EPO production was seen in rats in which EPO formation had been stimulated by exchange transfusion and the plasma viscosity of which was thereby altered by using exchange solutions of different composition to alter plasma viscosity and thus whole blood viscosity independently from hematocrit. Raising the gammaglobulin concentration to approximately 40 mg/ml plasma in the rats almost totally blunted the rise in serum EPO levels despite a fall of the hematocrit to 20%. Determination of renal EPO mRNA levels by RNase protection revealed that the reductions in serum EPO levels at higher plasma viscosities were paralleled by reductions in renal EPO mRNA levels. Taken together, our findings suggest that plasma viscosity may be a significant inhibitory modulator of anemia-induced EPO formation. The increased plasma viscosity in patients with hypergammaglobulinemias may therefore contribute to the inappropriate EPO production, which is a major reason for the anemia developing in these patients.

Iron stores and serum transferrin receptor levels during recombinant human erythropoietin treatment of anemia in rheumatoid arthritis

Ten rheumatoid arthritis (RA) patients with anemia of chronic disorders (ACD) were treated with recombinant human erythropoietin (r-Hu-Epo) using a dose of 250 U/kg s.c. 3 times a week for 6 weeks, in order to evaluate its effects on the anemia, iron stores, and serum-soluble transferrin receptor (sTfR) levels. All patients showed a rise in hemoglobin (Hb). Median Hb increased from 5.9 (5.5-7.0) at baseline to 6.7 (5.8-7.8) at 3 weeks and to 7.2 (5.9-8.5) mmol/l at 6 weeks during treatment. Ferritin levels decreased significantly during the 6 weeks, and five patients were iron deficient after 6 weeks of treatment. TfR levels increased significantly at 3 and 6 weeks during treatment. These preliminary findings may indicate that r-Hu-Epo is effective in improving ACD in RA. The sTfR rise may be explained by an increase in erythroid precursor cell mass or increased TfR expression and a decrease in tissue iron stores, although direct effects of Epo on TfR regulation cannot be excluded. Large double-blind studies with r-Hu-Epo in patients with RA and ACD are warranted.

Insulin-like growth factors decrease oxygen-regulated erythropoietin production by human hepatoma cells (Hep G2)

We examined the effects of insulin-like growth factors (IGFs) and insulin on erythropoietin (EPO) production by human hepatoma cells (Hep G2). Compared with normoxia (20% O2), EPO production by Hep G2 cells during a 72-h incubation was stimulated fivefold by exposure to low oxygen tension (1% O2) and nearly threefold by exposure to cobalt chloride (100 microM). IGF-I caused a concentration-dependent attenuation of EPO formation under normoxic conditions and inhibited (maximally 50%) EPO production stimulated by either low oxygen tension or cobalt [half-maximal effect (ED50) approximately 5 nM]. The increase of EPO mRNA levels in response to hypoxia was significantly reduced by IGF-I. Similarly to IGF-I, IGF-II (ED50 approximately 8 nM) and insulin (ED50 approximately 80 nM) also inhibited EPO formation in Hep G2 cells. IGF-I (100 pM-100 nM) stimulated the incorporation of radiolabeled alanine as a measure for total protein synthesis, 3H-labeled thymidine incorporation into DNA, and glycogen synthesis at 20 and 1% O2 in a concentration-dependent fashion. IGF-I exhibited a high affinity for the IGF-I receptor (apparent Kd approximately 3 nM). Unlabeled insulin was greater than 100-fold less potent than IGF-I in competing for 125I-IGF-I binding (apparent Kd approximately 360 nM). Conversely, insulin bound to the insulin receptor with high affinity (apparent Kd approximately 0.3 nM), whereas IGF-I was less than 1% as potent in competing for 125I-insulin binding. In summary, IGFs and insulin exert a negative control function on oxygen-regulated EPO production in Hep G2 cells. The inhibitory effect of IGFs and insulin on EPO formation appears to be mediated via the IGF-I receptor.

Inhibitory effect of zinc on stimulated erythropoietin synthesis in HepG2 cells

The effect of zinc on erythropoietin (EPO) synthesis in HepG2 cells was investigated. The increase in EPO synthesis induced by Co2+ (50 microM), Ni2+ (300 microM) or oxygen (1% O2) was inhibited by the presence of ZnCl2 (50-150 microM) in the tissue-culture medium, whereas basal EPO synthesis was unaffected. The effect was reflected by corresponding changes in the EPO mRNA level. These effects of zinc on EPO synthesis could not be mimicked by CdCl2 (less than or equal to 2 microM). Addition of FeCl3 to the medium appeared to decrease the inhibitory effect of zinc on hypoxia-induced EPO synthesis, implying that zinc may interfere with an iron-dependent step in EPO regulation.

Erythropoietin levels in patients depositing autologous blood in short intervals

Plasma immunoreactive erythropoietin (EPO) concentrations were studied in ten patients (7 men, 3 women) predonating autologous blood for hip arthroplasty. Donations were scheduled on day 1, 3, 7, 14 (and 21 if four units could not be donated previously). A predonation hemoglobin concentration of 11 g/dl was required. The donations led to a decline of the hemoglobin concentration from 14.1 +/- 1.0 g/dl (X +/- SD) prior to donation to 11.0 +/- 0.9 g/dl on day 15. EPO concentration prior to donation was 17.6 +/- 2.6 mU/ml. Each phlebotomy was followed by a rise in EPO levels that reached a peak concentration within 1 day. The highest concentration (35.8 +/- 15.0 mU/ml) was measured on day 16. The peak concentration was followed by a plateau at lower, although still elevated levels after the first and second donation, and by a slow, continuous decline after the third and fourth donation. This particular time course is similar to that during weekly donations [15]. The time integral of the EPO concentration during the first 3 weeks, however, was greater in the present study. This increased availability of EPO early during donation may lead to a more efficient stimulation of erythropoiesis.

Phorbol ester inhibits erythropoietin production in human hepatoma cells (Hep G2)

Using the human hepatoma cell line Hep G2, we have studied a possible role of protein kinase C (PKC) activity for regulation of erythropoietin (EPO) production. During a 72-h incubation, EPO production by the cells was stimulated sevenfold by exposure to low oxygen tension (1%) and threefold by exposure to cobaltous chloride (100 microM). The phorbol ester phorbol 12-myristate-13 acetate (PMA) led to a concentration-dependent inhibition of basal and stimulated EPO formation (ED50 10 nM). This decrease of EPO production, which was apparent already after 1 h of incubation with PMA, reached its maximal effect after 24 h and held on for 72 h. It was paralleled by an inhibition of the increase of EPO mRNA levels in response to stimulation. A 24-h preincubation of the cells with PMA (100 nM) virtually blunted the effect of hypoxia on EPO formation. Recovery of EPO synthesis after removal of PMA took 48-72 h. The effect of PMA on EPO production was mimicked by phorbol 12,13-dibutyrate (ED50 1 microM) but not by 4 alpha-phorbol 12,13-didecanoate. The synthetic diacylglycerol analogues oleolyl-acetylglycerol and dioctanoylglycerol (2-200 microM) also had no effect on either basal or stimulated EPO production. Treatment with PMA caused a translocation of the alpha-isoenzyme of PKC from the cytosol to the membrane after 1 h and a disappearance of the membrane-bound form after 24 h of incubation. Staurosporine and 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, two structurally different inhibitors of PKC activity, inhibited basal and stimulated EPO production with ED50 values of 9 nM and 50 microM, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-dependent expression of the erythropoietin gene in rat liver and kidneys

Using RNAse protection, we have made quantitative measurements of erythropoietin (EPO) mRNA in liver and kidneys of developing rats (days 1-54), to determine the relative contribution of both organs to the total EPO mRNA, to monitor changes which occur with development, and to compare the hypoxia-induced accumulation of EPO mRNA with the changes in serum EPO concentrations. To determine whether developmental and organ-specific responsiveness is related to the type of hypoxic stimulus, normobaric hypoxia was compared with exposure to carbon monoxide (functional anemia). Under both stimuli EPO mRNA concentration in liver was maximal on day 7 and declined during development. In contrast, EPO mRNA concentration in kidney increased during development from day 1 when it was 30-65% the hepatic concentration to day 54 when it was 12-fold higher than in liver. When organ weight was considered the liver was found to contain the majority of EPO mRNA in the first three to four weeks of life, and although, in stimulated animals, the hepatic proportion declined from 85-91% on day 1, it remained approximately 33% at day 54 and was similar for the two types of stimuli. When normalized for body weight the sum of renal and hepatic EPO mRNA in animals of a particular age was related linearly to serum hormone concentrations. However, the slope of this regression increased progressively with development, suggesting age-dependent alterations in translational efficiency or EPO metabolism.

Depressed serum erythropoietin in pregnant women with elevated blood lead

During the course of a prospective study of lead exposure and pregnancy outcome in 1,502 women, we tested the hypothesis that environmental lead exposure is associated with depressed serum erythropoietin concentration. At mid-pregnancy and at delivery, blood samples were stratified by hemoglobin concentration; within each hemoglobin stratum, sera of women with the lowest and highest whole blood lead concentrations were selected for serum erythropoietin analysis. Analysis of variance revealed that women with higher blood lead levels had inappropriately low serum erythropoietin at both mid-pregnancy and at delivery. Thus, depressed serum erythropoietin appears to indicate lead nephrotoxicity, and it may also be responsible for the anemia associated with lead poisoning.

Organ distribution of erythropoietin messenger RNA in normal and uremic rats

We used RNAase protection assays to measure low levels of erythropoietin messenger RNA (EPO mRNA) in the organs of unstimulated rats, and to compare basal and stimulated levels of EPO mRNA in the kidneys and extrarenal organs of rats rendered uremic by subtotal nephrectomy, with pair-fed controls. Using this sensitive assay, EPO mRNA was measured in the kidneys of unstimulated control animals and was detectable, at lower levels, in the liver and lung. After exposure to hypoxia, there was a 150-fold increase in renal EPO mRNA. Hepatic EPO mRNA was also greatly increased and accounted for 39 +/- 10% of the total. The small quantity of EPO mRNA in lung did not increase, but EPO mRNA became detectable in spleen. Animals subjected to subtotal nephrectomy became uremic and anemic (hematocrit 0.32 +/- 0.04 vs. 0.43 +/- 0.04 in controls, P = 0.002), but serum EPO concentrations were not significantly increased (32 +/- 9 vs. 24 +/- 6 mU/ml, P = 0.14). However, after hypoxic exposure, uremic animals increased serum EPO concentrations greatly, although the response was less than in controls (349 +/- 82 vs. 1009 +/- 238 mU/ml, P = 0.002). After hypoxia, extrarenal EPO mRNA levels in uremic animals were similar to controls. In particular, the large hepatic potential for EPO mRNA synthesis was unchanged but accounted for a greater proportion (84 +/- 5%) of the total EPO mRNA. The renal EPO mRNA content was reduced, as expected, after subtotal nephrectomy, but increased 50-fold after hypoxia. In this model of chronic renal failure, despite anemia, a large potential for EPO synthesis exists in liver and remnant kidney.

Oxygen-dependent erythropoietin production by the isolated perfused rat kidney

In this study we have investigated the role of oxygen delivery and of classic second messengers on erythropoietin production by the isolated perfused rat kidney. We found that the rat kidney was capable of de novo synthesis of erythropoietin. The erythropoietin production rate was inversely related to the oxygen pressure in the perfusate and increased from 0.17 to 1.85 U erythropoietin h-1 g kidney-1 when arterial PO2 was lowered from 500 mmHg to 30 mmHg. Addition of forskolin (10 microM) and 8-bromo-cGMP (100 microM) to the perfusate elicited significant effects on the renal vascular resistance, but had no significant effect on erythropoietin production. Hypoxia-induced erythropoietin formation, however, was blocked by calmidazolium (1 microM) and W-7 (10 microM), two structurally different putative calmodulin antagonists. Calmidazolium and W-7 had no effect on other functional parameters of the isolated perfused rat kidney such as flow rate, glomerular filtration rate or sodium reabsorption. Our findings suggest that the oxygen-sensing mechanism that controls renal erythropoietin production is primarily located in the kidney itself. A calcium/calmodulin-dependent cellular reaction could be involved in the signal transduction process.

The treatment of anaemia in the myelodysplastic syndromes with recombinant human erythropoietin

Recombinant human erythropoietin was administered subcutaneously to 10 patients with myelodysplasia (MDS) who had haemoglobin concentrations less than 10 g/dl, in an attempt to relieve their anaemia. Doses of 60 units/kg/d rising to 90 units/kg/d were given over a maximum period of 16 weeks. Two out of 10 patients showed a steady rise in haemoglobin concentration during treatment. One patient with refractory anaemia had a sustained rise from 9.9 g/dl to 11.3 g/dl, and one patient with refractory anaemia with excess blasts (RAEB) had a rise from 9.5 g/dl to 11.4 g/dl but then relapsed with the development of an iron deficient state. Serum concentrations of immunoreactive EPO varied considerably between patients, but both responders had relatively low baseline levels. Both responders were also new diagnoses and had received no red cell transfusions. The criteria for response to recombinant human erythropoietin therapy, as well as the indications for therapy remain to be clarified.

Role of erythropoietin in adaptation to hypoxia

The glycoprotein hormone erythropoietin (EPO) counteracts tissue hypoxia by increasing the systemic oxygen-carrying capacity. It induces augmentation of red blood cell mass by stimulating the formation and differentiation of erythroid precursor cells in the bone marrow. EPO production is increased under various forms of diminished oxygen supply such as anemic or hypoxic hypoxia. In the adult organism, the kidneys are the major source of EPO. The precise nature of the cells responsible for renal EPO production, however, has not yet been elucidated. Most likely, peritubular cortical cells, e.g. interstitial or endothelial cells, are involved in the elaboration of the hormone. From the observation that isolated perfused rat kidneys produce EPO in an oxygen-dependent fashion we conclude that the 'oxygen sensor' that controls hypoxia-induced EPO synthesis is located in the kidney itself. Within the kidneys, the local venous oxygen tension which reflects the ratio of oxygen supply to oxygen consumption is measured and transformed into a signal that regulates the formation of EPO. However, the mechanism by which a decrease of oxygen delivery to the kidneys is linked to an enhanced EPO gene expression is not yet known. Two possible mechanisms of regulation are discussed: First, renal hypoxia could lead to enhanced formation of metabolic mediators, for example prostaglandins or adenosine, which might stimulate EPO gene transcription by increasing cellular levels of second messenger molecules. Second, some kind of molecular 'oxygen receptor' such as a heme protein, that controls EPO formation by an oxygen-dependent conformational change, could mediate signal transduction.

Role of excretory graft function for erythropoietin formation after renal transplantation

To examine the role of renal excretory function for erythropoietin (EPO) formation we have determined the kinetics of plasma immunoreactive EPO (irEPO) in patients with end-stage renal disease undergoing renal allotransplantation (RTX). In 13 patients with immediate excretory graft function (imGF) and stable haemoglobin (Hb) concentrations (median Hb 9.5 g dl-1 and median irEPO 18 mU ml-1 before RTX) irEPO increased significantly on day 4 after RTX to a median value of 29 mU ml-1 and 2 days later reached a plateau of 34.4 +/- 3.3 mU ml-1 (mean +/- SD of daily median values during days 6-20). In patients with imGF having acute blood loss and subsequently receiving transfusions, irEPO responded in an inverse fashion to changes in Hb concentrations. In 12 patients with delayed graft function (dGF) (median Hb 8.8 g dl-1 and median irEPO 15 mU ml-1 before RTX) irEPO levels during the period of excretory failure remained either unchanged or displayed marked variations with peak values greatly exceeding those of patients with imGF. These variations were not related to changes in Hb concentrations and irEPO levels did not change following alterations in Hb concentrations. Upon recovery of excretory function irEPO approached the values found in patients with imGF. The results suggest that an intact excretory renal function is not a prerequisite for the capability to produce EPO, but correlates with the oxygen-dependent regulation of EPO formation.