Quantitation of ineffective erythropoiesis from the incorporation of [15N] delta-aminolaevulinic acid and [15N] glycine into early labelled bilirubin. I. Normal subjects

The long history of iron in the Universe and in health and disease

BACKGROUND

Not long after the Big Bang, iron began to play a central role in the Universe and soon became mired in the tangle of biochemistry that is the prima essentia of life. Since life's addiction to iron transcends the oxygenation of the Earth's atmosphere, living things must be protected from the potentially dangerous mix of iron and oxygen. The human being possesses grams of this potentially toxic transition metal, which is shuttling through his oxygen-rich humor. Since long before the birth of modern medicine, the blood-vibrant red from a massive abundance of hemoglobin iron-has been a focus for health experts.

SCOPE OF REVIEW

We describe the current understanding of iron metabolism, highlight the many important discoveries that accreted this knowledge, and describe the perils of dysfunctional iron handling.

GENERAL SIGNIFICANCE

Isaac Newton famously penned, "If I have seen further than others, it is by standing upon the shoulders of giants". We hope that this review will inspire future scientists to develop intellectual pursuits by understanding the research and ideas from many remarkable thinkers of the past.

MAJOR CONCLUSIONS

The history of iron research is a long, rich story with early beginnings, and is far from being finished. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.

Factors in the pathogenesis of the brain damage and anaemia in the Lesch-Nyhan syndrome

The possible factors in the pathogenesis of the brain damage and megaloblastic anaemia in the Lesch-Nyhan syndrome are discussed. Disordered growth and function appear to be limited to the brain, bone marrow and general body stature, yet the purine salvage enzyme hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8, HGPRT), although present in variable amounts in different tissues, is ubiquitous, a fact which suggests that other factors than HGPRT deficiency alone determine the pattern of tissue damage. Recent evidence suggests that the specific tissue damage in the Lesch-Nyhan syndrome is due to lack of NGPRT in tissues with relatively reduced purine de novo capability and a greater dependence on purine salvage pathways at certain stages in their development for their supply of purine ribonucleotides. This evidence is presented together with possible mitigating factors operating in the bone marrow.

Neocytolysis contributes to the anemia of renal disease

Neocytolysis is a recently described physiological process affecting the selective hemolysis of young red blood cells in circumstances of plethora. Erythropoietin (EPO) depression appears to initiate the process, providing the rationale to investigate its contributions to the anemia of renal disease. When EPO therapy was withheld, four of five stable hemodialysis patients showed chromium 51 (51Cr)-red cell survival patterns indicative of neocytolysis; red cell survival was short in the first 9 days, then normalized. Two of these four patients received oral 13C-glycine and 15N-glycine, and there was a suggestion of pathological isotope enrichment of stool porphyrins when EPO therapy was held, again supporting selective hemolysis of newly released red cells that take up the isotope (one patient had chronic hemolysis indicated by isotope studies of blood and stool). Thus, neocytolysis can contribute to the anemia of renal disease and explain some unresolved issues about such anemia. One implication is the prediction that intravenous bolus EPO therapy is metabolically and economically inefficient compared with lower doses administered more frequently subcutaneously.

Classification of anaemia on the basis of ferrokinetic parameters

Quantitative information on abnormalities of erythropoiesis and mechanisms of anaemia has been obtained in 136 anaemic patients by means of ferrokinetic studies. To derive a functional classification of anaemia based on ferrokinetic parameters, agglomerative hierarchical cluster analysis and principal coordinate analysis were utilized as techniques for unsupervised classification. Two main clusters were found and named anaemia with low potential erythropoiesis and with high potential erythropoiesis, since the most discriminant parameter between them was total erythroid iron turnover, a measure of total erythropoietic activity. A value of total erythropoiesis equal to 4 times the normal was found to discriminate these two types of anaemia in 94% of cases. Within the group with low potential erythropoiesis, three clusters showing different qualitative disturbances of erythropoiesis were singled out. Among patients with high potential erythropoiesis, two clusters were found. A value of effective erythropoiesis equal to 2.5 times the normal was shown to have a high discriminant power between these clusters. This threshold level distinguished between patients having ineffective erythropoiesis or peripheral haemolysis as the major mechanism of anaemia. The present functional classification of anaemia provides a complete picture of the different pathogenetic mechanisms and may represent the basis for a more rational diagnostic approach to erythroid disorders.

The contributions of erythropoietic and nonerythropoietic haem turnover to the early labelle peak of endogenous CO formation in man

The endogenous production of 14CO during the first week after administration of glycine-2-14C (early labelled peak, ELP) was determined in 13 healthy subjects. The subjects were studied during normal, suppressed or stimulated erythropoiesis induced by hypertransfusion and phlebotomy, respectively. The production of 14CO was calculated from determinations of the specific activity of the body CO store and the endogenous production of CO. The incorporation of labelled glycine into circulating red cell haemo;globin haem was calculated from the maximal specific activity of haemoglobin haem and the total amount of Hb. The average ELP was 73.0 X 10(3) disintegrations per min (dpm) and the incorportion of glycine into circulating haemoglobin haem 491 X 10(3) dpm in controls. The ELP and the incorporation of glycine increased by 86% and 92%, respectively, in phlebotomized subjects and decreased by 37% and 62%, respectively, in hypertransfused subjects. A linear regression equation was calculated for the relationship between ELP and erythropoiesis, expressed as the incorportion of glycine into circulating haemoglobin haem. The residual ELP remaining in the absence of erythropoiesis was 24.9 X 10(3) dpm calculated from data of all the subjects, and 32.8 X 10(3) dpm calculated from data of controls and hypertransfused subjects only. In conclusion, erythropoietic haem turnover was found to contribute about 60% and nonerythropoietic (mainly hepatic) haem turnover about 40% of the ELP in man.

Erythropoiesis and mean red-cell lifespan in normal subjects and in patients with the anaemia of active rheumatoid arthritis

Recently developed ferrokinetic methods offer a tool to measure effective and ineffective erythropoiesis and mean red-cell lifespan (Ricketts et al, 1975). We have used this tool to investigate erythropoiesis in normal subjects and in patients with the anaemia of active rheumatoid arthritis. In normal subjects the results are comparable with the results published by Cavill et al (1977). In patients with the anemia of active rheumatoid arthritis there appears to be a total and an effective red-cell production as in the normal subjects. The ineffective erythropoiesis in the patients is increased and the produced red cells have a shortened mean lifespan in the circulation. The increased ineffective erythropoiesis is probably due to inadequate supply of iron to the marrow and the shortened mean red-cell lifespan to an extra-corpuscular haemolytic factor. The impaired marrow response to the anaemia of active rheumatoid arthritis has been confirmed.

Estimation of ferrokinetic parameters by a mathematical model in patients with primary acquired sideroblastic anaemia

Ferrokinetic parameters were estimated in eight patients with primary acquired sideroblastic anaemia (PASA) by means of a mathematical model of iron kinetics. Both plasma 59Fe clearance and red cell utilization curves were used to identify the model parameters. The close agreement between experimental and theoretical data proved that the model can describe iron kinetics in sideroblastic anaemia. Ineffective erythropoiesis was found to be major factor in the production of the anaemia. Various degrees and patterns of peripheral haemolysis were observed. The storage iron was always markedly increased and a large non-erythroid iron turnover was calculated in the most severely affected patients. The results are compared with present knowledge of erythropoiesis in PASA.

[Erythropoiesis in iron deficiency]

The kinetics of erythroblast proliferation were studied by means of quantitative 14C-autoradiography in 5 patients showing anemia due to infection or malignancy, in 7 patients suffering from iron deficiency anemia, and in two individuals with bleeding enemia. Compared with a group of 5 healthy persons a markedly reduced turnover of erythroblasts was found in the anemia due to infection, malignancy, and iron deficiency, whereas this turnover was normal or increased in the case of bleeding anemia. The reduction is caused by a progressively decreasing rate of erythroblast proliferation and maturation with advancing development into mature cells. No indications of a change in the number of cell divisions were found in the anemia of infection, malignancy, and of iron deficiency, nor was there evidence of an intramedullary death of nucleated red cell percursors. The imbalance between production and loss of red cells causing anemia shows a different pattern in the 3 groups of disease: In bleeding anemia the insufficiency of supply is not yet apparent from the rate of erythroblast turnover giving weight to the factor of blood loss. In anemia due to infection, malignancy, and iron deficiency the but moderately increased rate of red cell destruction cannot be compensated because of several impairments: The rate of erythroblast turnover is reduced, and, in addition, a moderate portion of maturing cells is destroyed, probably at the reticulocyte stage. As the most significant factor, the bone marrow is unable to compensate the anemia by an effective erythroblast hyperplasia. In iron deficiency this hyperplasia is inadequately low, in infection and malignancies, however, it is more or less missing.

Role of ineffective erythropoiesis in the anaemia of rheumatoid arthritis

The importance of inadequate haemoglobin synthesis and ineffective erythropoiesis in the anaemia of rheumatoid arthritis was studied by measuring the incorporation of 15N glycine into haemoglobin haem and early labelled bilirubin in a patient with severe anaemia before and after response to gold therapy. Initially, total erythroid haem turnover was decreased but haem turnover due to ineffective erythropoiesis was markedly increased, accounting for 29% of total erythroid haem turnover. Gold therapy resulted in marked clinical improvement, accompanied by a rise in haemoglobin to normal. Total erythroid haem turnover increased and the percentage ineffective erythropoiesis fell to normal. Ineffective erythropoiesis may thus be an important reversible factor in the production of the anaemia of rheumatoid arthritis.

Reversal of ineffective erythropoiesis in pernicious anaemia following vitamin B12 therapy

Ineffective erythropoiesis was quantitated in a series of patients with pernicious anaemia at different times in relation to vitamin B12 therapy by measuring the incorporation of [15N]delta aminolaevulinic acid and [15N]glycine into early labelled bilirubin. Prior to therapy ineffective erythropoiesis was grossly increased but this was reversed within 24 h of giving vitamin B12, suggesting that most of the existing megaloblasts are enabled to mature into circulating red cells.

Congenital dyserythropoietic anaemia: response to splenectomy and quantitation of ineffective erythropoiesis

The clinical and haematological features of an unusual case of congenital dyserythropoietic anaemia are described. There was a pronounced haemolytic component to the anaemia, with a mean cell life of five days, and a remarkable response to splenectomy. Measurement of the incorporation of 15N glycine into the haem of circulating red cells and into bilirubin showed that haem turnover due to ineffective erythropoiesis was increased 45 times compared with a control group (11.63 mg/kg/day, NR = 0.26 + 0-10) and represented 51% of total erythroid haem turnover.

Quantitation of ineffective erythropoiesis from the incorporation of [15N] delta-aminolaevulinic acid and [15N] glycin into early labelled bilirubin. II. Anaemic patients

The incorporation of [15N]delta-aminolaevulinic acid and [15N glycine into haemoglobin haem and early labelled bilirubin was measured in subjects with various haematological disorders. The clearance of [14C bilirubin was used to measure bilirubin production rate, and the magnitude of the various sources of bilirubin production and the percentage ineffective erythropoiesis were calculated. Ineffective erythropoiesis was found to be a major factor in the production of the anaemia in patients with the following disorders: megaloblastic anaemia associated with the Lesch-Nyhan syndrome, thalassaemia intermedia, sideroblastic anaemia, and the anaemia of chronic disorders. In three patients with iron-deficiency anaemia ineffective erythropoiesis was increased, but was of minor importance in the production of the anaemia, while in two patients with aplastic anaemia and one with macrocytosis of alcoholism there was no increase in ineffective erythropoiesis.