Erythroid marrow function in anemic patients

Erythropoietic activity is known to be closely associated with marrow iron uptake. A modification of the standard measure of plasma iron turnover has been developed in which erythron transferrin uptake (ETU) rather than iron uptake has been calculated. The ETU has the advantage of providing a parameter of erythroid marrow activity independent of change produced by plasma iron and transferrin saturation. Measurements in 80 patients with anemia were compared to the normal value of 60 +/- 12 mumol/L whole blood/d. The mean ETU for ten patients with severe aplastic anemia and for six patients with pure red-cell aplasia were 12 +/- 8 and 12 +/- 11 mumol/L whole blood/d, respectively. In ten transfusion-dependent patients with renal failure under dialysis therapy, the mean value was 35 +/- 11, while ten other dialyzed patients who were transfusion independent had a mean ETU of 73 +/- 21 mumol/L whole blood/d. Sixteen patients with hemolytic anemia had an average ETU of 400 +/- 130, while 28 patients with ineffective erythropoiesis had a mean value of 474 +/- 147 mumol/L whole blood/d. While patients with hypoproliferative anemia showed no relation between the severity of anemia and ETU, those with hyperproliferative erythroid marrow showed increasing values as the anemia became more severe. Sequential measurements in patients with aplastic anemia under treatment and in thalassemic patients under transfusion therapy showed the value of this measurement in monitoring the effects of treatment on erythroid marrow activity. It is concluded that the measurement of ETU provides a more direct ferrokinetic evaluation of erythroid activity in anemic states.     

Transferrin metabolism in alcoholic liver disease

The metabolism of transferrin was studied using purified 125I-labeled transferrin in 11 alcoholic patients; six with fatty liver and five with cirrhosis. Six healthy subjects whose alcohol intake was les than 40 gm daily were studied as a control group. There were no significant differences in the mean fractional catabolic rate and plasma volume in the alcoholic groups when compared with control subjects. A significantly decreased mean serum transferrin concentration was found in the alcoholic cirrhotic patients (1.8 +/- 0.3 gm per liter vs. 2.9 +/- 0.2; p less than 0.01), resulting from diminished total body synthesis (0.9 +/- 0.2 mg per kg per hr vs. 1.8 +/- 0.2; p less than 0.01). In contrast, in the patients with alcoholic fatty liver, the mean total body transferrin synthesis (2.4 +/- 0.3 mg per kg per hr) was significantly increased when compared with controls (p less than 0.05). For all the alcoholic patients, the serum transferrin correlated with transferrin synthesis (r = + 0.70; p less than 0.01) but the serum iron did not. These results suggest that, in alcoholic cirrhosis, transferrin synthesis is decreased, probably reflecting diminished synthetic capacity by the liver. In contrast, in patients with alcoholic fatty liver, transferrin turnover is accelerated.     

Iron metabolism in patients with the anaemia of end-stage renal disease during treatment with recombinant human erythropoietin

Iron metabolism was studied in 21 patients with the anaemia of end-stage renal disease during 40 weeks of treatment with recombinant human erythropoietin (rhEPO). Oral iron was prescribed to all patients. Initial serum iron concentrations and transferrin saturation levels were subnormal, decreased during the correction period of treatment, and increased thereafter. In 81% of patients in whom pretreatment transferrin saturation was below 0.25, transferrin saturation decreased below 0.16, despite sufficiently high serum ferritin levels. Serum ferritin concentrations decreased significantly. There was no correlation between serum ferritin levels and serum iron or transferrin saturation. Ferrokinetic studies, performed before and during treatment, showed an increase in plasma iron turnover, in erythron transferrin uptake, and in the flux of iron binding sites through the plasma. The rhEPO dose needed to keep the haematocrit at the target level during the maintenance period of treatment was significantly correlated with transferrin saturation, and iron binding capacity, but not with serum ferritin concentrations. This suggests that the functional availability of iron in plasma, rather than the size of body iron stores, is a major factor in the determination of the response to rhEPO treatment in end-stage renal disease.     

Ferrokinetic measurement of erythropoiesis

Ferrokinetic measurements have proved useful because of the dominant role of the erythron in tissue iron uptake. Detailed measurements of the plasma iron disappearance curve coupled with in vivo counting have defined the major pathways of iron utilization and early refluxes of iron into plasma. Recent studies have disclosed two separate plasma kinetic pools consisting of mono- and diferric transferrin, and have demonstrated the effect of their relative abundance on tissue iron uptake. Allowance for the amount of each has made possible the calculation of iron-bearing transferrin uptake, which is independent of plasma iron concentration as long as receptors are saturated. This refinement permits the measurement of functional erythron transferrin receptors, and thereby the relative number of immature erythroid cells.     

Iron metabolism in the Belgrade rat

Iron metabolism in the Belgrade rat was examined in the intact animal and in the reticulocyte suspensions. The plasma iron turnover was increased. However, when allowance was made for the effect of the elevated plasma iron concentration, erythroid marrow capacity for iron uptake was at basal levels. Numbers of erythroid cells in marrow and spleen measured by the radioiron dilution technique were increased. Thus iron uptake was not proportionate to the erythroid hyperplasia in the b/b rat, despite a more than adequate plasma iron supply. This relative deficiency in iron uptake was reflected in a severe microcytosis and elevated red cell protoporphyrin. Reticulocyte incubation studies demonstrated an unimpaired uptake of the transferrin- iron-receptor complex but a marked reduction in iron accumulation. The diferric transferrin molecule, when it did give up iron within the cell, released both of its iron atoms so that only apotransferrin was returned to the media. In contrast to the nearly complete release of iron within the normal reticulocyte, the major portion of iron taken up by the Belgrade reticulocyte was returned to the plasma. The release mechanism that can be impaired in iron-deficient reticulocytes by EDTA or cadmium was shown to be affected by lower concentrations of these substances in the Belgrade reticulocyte. It is concluded that the Belgrade rat has an abnormality of iron release within the absorptive vacuole that is responsible for a state of intracellular iron deficiency, involving the erythron and other body tissues.     

The soluble transferrin receptor in dysplastic erythropoiesis in myelodysplastic syndrome

OBJECTIVES: In individuals without iron deficiency, the soluble transferrin receptor (sTfR) directly reflects the erythropoietic activity. This study investigated sTfR concentrations in ineffective, dysplastic erythropoiesis in myelodysplastic syndrome (MDS). METHODS: To exclude influences of other myeloid cells on sTfR, only patients with refractory anemia (RA), refractory anemia with ringed sideroblasts (RARS) and 5q(-) syndrome were included. sTfR was measured nephelometrically (normal range 0.81-1.75 mg/L). RESULTS: Thirty-four untreated MDS patients (RA = 14, RARS = 10, 5q(-) syndrome = 10) were enrolled and analysed. The mean sTfR value of all MDS patients (1.30 +/- 0.8 mg/L, range 0.2-3.8) did not differ from our control group. In 5q(-) syndrome, the mean sTfR concentration (0.80 +/- 0.5 mg/L) was significantly lower than in RA (1.32 +/- 0.4 mg/L, P = 0.02) and RARS (1.75 +/- 1.1 mg/L, P = 0.03). Subdividing MDS according to their amount of erythroid mass in bone marrow a significant difference of sTfR between patients with decreased (0.70 +/- 0.4 mg/L), normal (1.32 +/- 0.4 mg/L) and increased (2.06 +/- 0.9 mg/L) erythropoiesis was observed. MDS patients with sTfR values below the reference range of 0.81 mg/L required transfusions in 90% of cases and showed higher erythropoietin levels compared to MDS patients with sTfR levels > or =0.81 mg/L (P = 0.01). There was a good agreement between sTfR and the amount of polychromatic erythroblasts observed (r = 0.68, P < 0.001). CONCLUSION: In conclusion, the serum concentration of sTfR reflects erythropoietic activity in MDS, but it is in particular determined by the degree of erythroid maturation and the severity of ineffective erythropoiesis. Low sTfR values in MDS are associated with a reduced, poorly differentiated erythropoiesis and requirement of blood transfusions.     

Plasma radioiron kinetics in man: explanation for the effect of plasma iron concentration.

The plasma iron turnover was measured in 19 normal subjects. A correlation was found between plasma iron concentration and plasma iron turnover. In addition to the turnover of 55Fe at normal plasma iron concentration (predominantly monoferric transferrin), a second turnover in which the labeled plasma was saturated with iron (to produce predominantly diferric transferrin) was studied with 50Fe. It was demonstrated that diferric transferrin had a greater rate of iron turnover but that the distribution between erythroid and non-erythroid tissues was unchanged. It was concluded that plasma iron turnover is dependent on the monoferric/diferric transferrin ratio in the plasma but that the internal distribution of iron is unaffected.     

Effects of bucindolol on neurohormonal activation in congestive heart failure.

To examine the effects of beta-adrenergic blockade on neurohormonal activation in patients with congestive heart failure, 15 men had assessments of hemodynamics and supine peripheral renin and norepinephrine levels before and after 3 months of oral therapy with bucindolol, a nonselective beta antagonist. At baseline, plasma renin activity did not correlate with any hemodynamic parameter. However, norepinephrine levels had a weak correlation with left ventricular end-diastolic pressure (r = 0.74, p less than 0.01), stroke volume index (r = 0.61, p less than 0.02) and pulmonary vascular resistance (r = 0.54, p less than 0.05). Plasma renin decreased with bucindolol therapy, from 11.6 +/- 13.4 to 4.3 +/- 4.1 ng/ml/hour (mean +/- standard deviation; p less than 0.05), whereas plasma norepinephrine was unchanged, from 403 +/- 231 to 408 +/- 217 pg/ml. A wide diversity of the norepinephrine response to bucindolol was observed with reduction of levels in some patients and elevation in others. Although plasma norepinephrine did not decrease, heart rate tended to decrease (from 82 +/- 20 vs 73 +/- 11 min-1, p = 0.059) with beta-adrenergic blockade, suggesting neurohormonal antagonism at the receptor level. No changes in I-123 metaiodobenzylguanidine uptake occurred after bucindolol therapy, suggesting unchanged adrenergic uptake of norepinephrine with beta-blocker therapy. Despite reductions in plasma renin activity and the presence of beta blockade, the response of renin or norepinephrine levels to long-term bucindolol therapy did not predict which patients had improved in hemodynamic status (chi-square = 0.37 for renin, 0.82 for norepinephrine).(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of iron absorption and storage iron turnover

The regulation of iron supply to plasma was studied in male rate. Repeated exchange transfusions were first carried out with plasma from iron-deficient or iron-loaded animals. There was no recognizable effect on the amount of iron entering the plasma as evidenced by plasma iron concentration or iron absorption by recipient animals. In other studies, iron compounds having different tissue distribution were injected. Subsequent iron release was greater from reticuloendothelial cells than from other iron-loaded tissues. When requirements for transferrin iron were increased by exchange transfusion with high reticulocyte blood, within minutes there was a doubling of the rate of tissue iron donation. It was concluded from these studies that (1) iron turnover in the plasma is primarily determined by the number of tissue receptors for iron, particularly those of the erythron, (2) that the amount of iron supplied by each donor tissue is dependent on the output of other donor tissues, and (3) that a humoral mechanism regulating iron exchange is unlikely in view of the speed of response and magnitude of changes in plasma iron turnover. It is proposed that there is some direct mechanism that determines the movement of iron from donor tissues to unsaturated transferrin binding sites.     

Atrial natriuretic factor, catecholamines and the renin-angiotensin system in cardiac insufficiency. Relation to hemodynamic parameters

Plasma concentrations of atrial natriuretic factor (ANF), catecholamines (adrenaline, noradrenaline, dopamine) and aldosterone, and plasma renin activity (PRA) were measured in a group of 20 patients with moderate to medium heart failure (NYHA class II 7 patients, class III 13 patients), 24 hours after treatment was discontinued. Compared with a control group, plasma concentrations of ANF (p less than 0.01), noradrenaline (p less than 0.05), aldosterone (p less than 0.01) and PRA (p less than 0.01) were significantly increased. There was a significant difference between class II patients and class III patients in plasma ANF (p less than 0.01) and noradrenaline (p less than 0.02) concentrations, but not in PRA and aldosterone levels. A significant correlation was observed between plasma ANF concentration and left ventricular end-diastolic pressure (r = 0.68, p less than 0.001), pulmonary arterial pressure (r = 0.59, p less than 0.01), pulmonary capillary pressure (r = 0.51, p less than 0.02), cardiac index (r = 0.46, p less than 0.05) and left ventricular end-diastolic volume (r = 0.50, p less than 0.05). However, ANF concentration was not correlated with mean right atrial pressure. Plasma adrenaline concentration correlated with systemic arterial resistance (r = 0.80, p less than 0.001), pulmonary arterial pressure (r = 0.57, p less than 0.02), mean pulmonary capillary pressure (r = 0.62, p less than 0.001), cardiac index (r = 0.53, p less than 0.05) and left ventricular end-diastolic pressure (r = 0.58, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Lithium-sodium countertransport in erythrocytes of normal and hypertensive subjects. Relationship with age and plasma renin activity

Lii-Nao countertransport was measured in red blood cells of 58 normotensive subjects (27 females and 31 males), 60 patients with essential hypertension (26 females and 34 males), and in 28 with secondary hypertension (19 females and 9 males). The mean values (+/- SEM) expressed as mmol Li (1 red cells X hr)-1 were 0.18 +/- 0.02 (females) and 0.20 +/- 0.01 (males) in the control group, 0.34 +/- 0.04 (females) and 0.39 +/- 0.03 (males) in essential hypertension, 0.16 +/- 0.03 (females) and 0.19 +/- 0.02 (males) in secondary hypertension. The mean value of Lii-Nao countertransport obtained in essential hypertension was statistically different from those obtained in both normals (p less than 0.001) and patients with secondary hypertension (p less than 0.001). A negative correlation was found between age and Lii-Nao countertransport in normotensive males (r = - 0.648; p less than 0.001) but neither in normal females nor in patients with essential hypertension. A positive correlation (r = + 0.425; p less than 0.05) was found between plasma renin activity after intravenous furosemide and Lii-Nao countertransport in essential hypertension. These findings support the hypothesis of a characteristic cation transport across the red blood cell membrane of patient with essential hypertension which might be correlated with the plasma renin activity.     

The clinical significance of the measurement of plasma transferrin as a growth factor. II. The changes in various endocrine status

The clinical significance of the measurement of plasma transferrin (Tf) in patients with hypophysial disorders was reported in our previous papers. In the present study, we determined plasma Tf levels in 55 patients with various endocrine states and considered their clinical significance compared with plasma somatomedin-C (SM-C) levels. Plasma Tf levels decreased significantly in patients with anorexia nervosa (p less than 0.02), hyperthyroidism (p less than 0.05), primary hypothyroidism (p less than 0.05) and Cushing's syndrome (p less than 0.05), while they were elevated significantly in pregnancy (p less than 0.01) or females using estrogens (p less than 0.05). The former two declines were considered a reflection of the malnutritional state of the patients since a significant negative correlation was observed between plasma Tf levels and the percentile deficit from the ideal body weight in patients with anorexia nervosa (p less than 0.01), or between plasma Tf levels and elevated T3 levels which induce hypermetabolism in patients with hyperthyroidism (p less than 0.01). A significant correlation was observed between the SM-C and Tf levels in these subjects (including normal controls and patients with hypophysial disorders) as a whole (r = 0.79, p less than 0.001). These data indicate that plasma Tf is changeable according to the endocrinological and nutritional conditions with good correlation to the SM-C, and it is suggested that Tf also operates as a growth factor in vivo.     

Erythropoietin activity in the serum of beta thalassemic patients

Serum erythropoietic activity was determined in 32 patients with beta thalassemia major and intermedia. Quantitation was performed by an in vitro bioassay using rabbit erythroid precursor cells (CFU-E) either by colony assay or by 3H-thymidine uptake. 20 polytransfused beta-thalassemic major patients had erythropoietic activity (mean 89.3 +/- 36 milliunits/ml) which was not significantly different (p greater than 0.2) from normal individuals (51.3 +/- 32 milliunits/ml). 12 untransfused patients with beta thalassemia intermedia were found to have comparable serum erythropoietic activity (p greater than 0.01). These levels were much lower than those found in patients with aplastic anemia who had a comparable degree of anemia. We have shown that the low EPO activity in thalassemic patients was not due to experimental conditions (excess of ferritin, low transferrin) nor to specific inhibitors appearing in this disease. No correlation was found between the erythropoietic activity and sex or other clinical parameters of the patients such as severity of the anemia, splenectomy, iron chelation or transfusion therapy. 4 young thalassemic children (1-2 yr of age) studied had high erythropoietic activity ranging from 661 to 5793 milliunits/ml--significantly different from normal children of the same age. It is suggested, therefore, that a decrease in serum erythropoietin levels develops during the course of the disease.     

Relationship among plasma iron, plasma iron turnover, and reticuloendothelial iron release

A circadian rhythm was demonstrated in 10 males and 10 females with respective mean decreases in plasma iron concentration at 18 hr of 62% and 47% of morning values. Ferrokinetic studies performed on 5 normal males and 5 normal females showed a more rapid disappearance rate and lower plasma iron turnover in the evening. Parallel studies were done on 6 normal males in the morning and 4 normal males in the evening of the release of reticuloendothelial iron at 8 and 18 hr after intravenous injection of 59Fe chondroitin ferrous sulfate. The 6-hr release in the morning was 54.1% and in the evening 25.9%. Composite data from morning and evening showed a correlation between plasma iron level and plasma iron turnover (r = 0.76, p less than 0.001). A similar correlation existed between the plasma iron level and the percent of radioiron released from the reticuloendothelial system (r = 0.67, 0.02 less than p less than 0.05). These data are consistent with a fluctuating iron release from the reticuloendothelial cell in normal subjects, which would account for the diurnal variation in plasma iron.     

In vitro and in vivo studies of iron delivery by human monoferric transferrins

S ummary . According to the Fletcher-Huehns hypothesis there exists a functional difference between the two iron-binding sites of transferrin. In this study we present the results of an evaluation of this hypothesis in vitro and in vivo with human pure monoferric transferrins obtained by preparative isoelectric focusing in granulated gels. The uptake of iron from monoferric transferrins TfFe_c and Fe_NTf by erythroid bone marrow cells, hepatocytes and stimulated T-lymphocytes in vitro was equal, even when both monoferric transferrins were present together in the incubation medium. Ferrokinetic studies in vivo , performed with both pure monoferric transferrins, showed that transferrin TfFe_c, as well as transferrin Fe_NTf, mainly deliver their iron to the erythron. As red cell ⁵⁹Fe utilization, red cell iron turnover and other ferrokinetic parameters, obtained from this study, were identical too it is evident that both iron-binding sites of transferrin are functionally homogeneous in vivo , with respect to iron delivery.     

Serum ferritin in refractory anemias

The relationship between the level of erythropoiesis and iron balance was evaluated in 13 subjects with idiopathic refractory anemias. Serum ferritin levels and bone marrow iron stores were increased only in those patients with ring sideroblasts, erythroid hyperplasia and ineffective erythropoiesis. The magnitude of the increase correlated with the duration of anemia and the degree of increase in the erythron iron turnover. Ferritin levels were not related to the severity of the anemia, indicating that increased iron stores did not represent a shift of iron from the erythron or an absorption response to anemia per se. It does suggest that the level of erythroid proliferation directly affects gastrointestinal iron absorption, which in time leads to iron overload.     

Bicyclo-prostaglandin E2 metabolite in congestive heart failure and relation to vasoconstrictor neurohumoral principles

Vasodilator prostaglandins may play a role in maintaining circulatory homeostasis in patients with congestive heart failure (CHF). Plasma levels of bicyclo-prostaglandin E2 metabolite (PGEm), a chemically stabilized degradation product of the vasodilator prostaglandin E2, were determined in 45 patients with chronic CHF (New York Heart Association class II, III or IV). Mean circulating levels of bicyclo-PGEm were significantly elevated in patients with functional class III (72 +/- 8 pg/ml) or IV CHF (77 +/- 10 pg/ml) compared with control subjects (49 +/- 3 pg/ml) and patients with functional class II CHF (49 +/- 4 pg/ml). Bicyclo-PGEm concentrations correlated with plasma renin activity (r = 0.68, p less than 0.001) and plasma angiotensin II (r = 0.56, p less than 0.001) and plasma noradrenalin levels (r = 0.34, p less than 0.05). An inverse correlation was found between serum sodium concentrations and levels of bicyclo-PGEm (r = 0.46, p less than 0.01) as well as plasma renin activity (r = 0.66, p less than 0.001). Thus, prostaglandin E2 levels in plasma are increased in patients with severe CHF.     

Urinary transferrin excretion in type 1 (insulin-dependent) diabetes mellitus.

Urinary excretion of transferrin and albumin was studied by radioimmunoassay in 47 adult patients with Type 1 diabetes and 28 control subjects. Median (range) urinary transferrin excretion rate was significantly elevated in the diabetic group 0.58 (0.02-2663.3) micrograms min-1 compared with the control group 0.04 (0.01-0.28) micrograms min-1, p less than 0.001. Urinary transferrin:creatinine ratios (x 10(2)) were different in diabetic 47 (0.6-958.0) micrograms mmol-1 and control groups 0.7 (0.06-2.3) micrograms mmol-1, p less than 0.001). There were correlations between urinary transferrin and albumin excretion rates in diabetic (r = 0.78, p less than 0.001) and control groups (r = 0.81, p less than 0.05). Forty (85%) diabetic patients had elevated transferrin excretion rates, 18 (38.3%) had elevated albumin excretion rates. All diabetic patients with elevated albumin excretion rates had elevated transferrin excretion rates. Twenty-one (77.8%) of the patients with normal albumin excretion rates had elevated transferrin excretion rates. Urinary excretion of N-acetyl-beta-D-glucosaminidase was greater in diabetic patients than control subjects (142 vs 58 mumol h-1 l-1, p less than 0.001). There were correlation between transferrin and N-acetyl-beta-D-glucosaminidase excretion (r = 0.67, p less than 0.01) and albumin and N-acetyl-beta-D-glucosaminidase excretion (r = 0.63, p less than 0.01) in the diabetic group. Elevated urinary transferrin excretion rate may be a marker for renal dysfunction in diabetes mellitus.     

The relationship between plasma iron and plasma iron turnover in the rat

Plasma iron turnover has been evaluated in the growing rat. Consistent data were obtained with the intravenous injection of radioiron in the form of ferrous sulfate or ferric citrate. Plasma iron turnover changed as a function of plasma iron concentration. Only part of this effect in the rat was due to the different rates of clearance of mono-and differic transferrin, the latter having a higher iron delivery rate in vivo. An additional effect was shown to relate to the rate of red cell production. With decreased production, the effect of plasma iron on plasma iron turnover was reduced, whereas with increased erythropoiesis there was an additional increment in plasma iron turnover for any increase in plasma iron. Since this effect was observed when increased iron demands were due to an increase in erythroid precursors in the marrow but not in the circulating blood, it is attributed to limitations in iron flow to the marrow. This suggests that erythroid marrow activity and the adequacy of iron supply when studied by ferrokinetic techniques can best be defined by the response curve relating plasma iron concentration to plasma iron turnover.     

Transferrin receptor expression in the human placenta

Iron transport from the mother to the fetus is mediated by transferrin receptors located at the maternofetal interface of the placenta. Transferrin receptors bind iron-loaded transferrin molecules from the maternal plasma, thus allowing iron uptake by trophoblastic cells which then deliver the metal to the fetal plasma. We have measured the transferrin receptor content in the placentas from 16 normal-term pregnancies and investigated the relationships between transferrin receptor expression and non-haem iron content, as well as maternal and fetal iron status. Transferrin receptor content was evaluated indirectly by determining the transferrin binding capacity of a placenta extract. Transferrin receptor content of the placenta ranged from 20 to 154 micrograms/g of tissue, with a mean value of 96 +/- 37 micrograms/g. The mean non-haem iron content was 78 +/- 11 micrograms/g of tissue, corresponding to 47 +/- 10 mg for the whole placentas. The amount of transferrin receptors in the placenta was found to be inversely related to the amount of non-haem iron (r = 0.64; p less than 0.025). No significant relationship was observed between each of these two parameters and the iron status of either the mother or the fetus. We conclude that placental non-haem iron, which represents a storage form of this element, is likely to play a regulatory role in the expression of transferrin receptors, and consequently in the process of iron uptake by the placenta.