Bone marrow and peripheral blood globin chain biosynthesis in iron deficiency

Alpha- and beta-globins of the anemic Belgrade laboratory rat. II. The effect of hemin and iron-dextran treatment

We have studied the changes in bone marrow and spleen globin chain levels after in vivo hemin and iron-dextran treatment of hereditarily anemic Belgrade laboratory (b/b) rats. The increase of globin chains was detected in the bone marrow and in the spleen when b/b animals were treated with either iron or hemin. The analysis of changes in alpha- and beta-globin chain ratios revealed the distinctive role of these molecules in regulating globin chain status. Iron-dextran, as expected, ameliorated the imbalance of alpha- and beta-globin chains in the b/b rat spleen. On the other hand, hemin, as we have hypothesized in the accompanying paper, leads to a surplus of beta-globin chains in the bone marrow, similar to the one detected in the b/b rat spleen. Therefore, an iron-rich microenvironment has a stimulatory effect, while a hemin-rich microenvironment has an inhibitory effect on erythropoiesis.

Globin chain synthesis ratios in sideroblastic anaemia

Globin synthesis ratios were measured on reticulocytes from nine patients with primary acquired sideroblastic anaemia (SA), four patients with hereditary or congenital SA, two patients with secondary acquired SA and three patients with iron deficiency (ID). Ten of the samples from patients with SA and all the samples from patients with ID had normal ratios. Samples from three patients had significantly abnormal ratios, one from a patient with SA and acquired Hb H disease (alpha/beta 0 X 26), one from a patient with secondary acquired SA (alpha/beta 0 X 88), and one from a patient who went on to develop acute myeloblastic leukaemia (alpha/beta 1 X 36). Globin synthesis was stimulated by 100 microM haem similarly in normal, SA and ID reticulocytes. Any limitation of globin synthesis in SA and ID is therefore not easily reversible by adding haem. Inhibition of haem synthesis in nonsideroblastic reticulocytes using 4 mM isonicotinic acid hydrazide for 1 h incubation affected neither total globin synthesis nor the alpha/beta ratio. These results contradict the view that decreased haem synthesis decreases globin chain synthesis and decreases the alpha/beta globin chain synthesis ratios in human reticulocytes. Previously reported findings that haem could reverse globin chain synthesis inhibition in SA were good evidence for a primary deficiency of haem synthesis in the erythroblasts of these patients. Our inability to substantiate these findings emphasizes the need for a re-evaluation of the aetiology of sideroblastic anaemia.