vitamin-b-12 and Leukemia--Erythroblastic--Acute

The plasma protein transcobalamin II (TCII) binds and delivers cobalamin (Cbl; vitamin B12) to all cells, which internalize the TCII/Cbl complex by receptor-mediated endocytosis. Congenital deficiency of TCII results in intracellular Cbl deficiency, one effect of which is to disrupt DNA synthesis, leading to megaloblastic anemia. We report here an in vitro culture system in which cell growth is dependent on delivery of Cbl to cells by TCII. Recombinant human holo-TCII was shown to support in dose-dependent manner the growth of the human erythroleukemic cell line K562 and the murine lymphoma cell line BW5147. Free Cbl also supported cell growth; however, at 100- to 1,000-fold higher concentrations than those effective in the presence of apo-TCII. To determine if cellular depletion of Cbl could be achieved by interfering with interactions between TCII/Cbl and its cell-surface receptor, several monoclonal antibodies raised against human TCII were studied. Three antibodies, found to compete for the same binding site on TCII, proved to be effective inhibitors of TCII/Cbl-dependent cell growth. Our results suggest that monoclonal anti-TCII antibodies that block the function of this protein may prove useful in antitumor therapies.

Topics: Antibodies, Monoclonal; Apoptosis; Cell Division; Folic Acid; Growth Inhibitors; Humans; Leukemia, Erythroblastic, Acute; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Lymphoma; Neoplastic Stem Cells; Transcobalamins; Tumor Cells, Cultured; Vitamin B 12

Plasma membrane receptors for the serum cobalamin-binding protein transcobalamin II (TCII) were identified on human leukemia K562 and HL-60 cells using immunoaffinity-purified human TCII labeled with [57Co]cyanocobalamin. The Bmax values for TCII receptors on proliferating K562 and HL-60 cells were 4,500 and 2,700 per cell, respectively. Corresponding dissociation constants (kd) were 8.0 x 10(-11) mol/L and 9.0 x 10(-11) mol/L. Rabbit TCII also bound to K562 and HL-60 cells but with slightly reduced affinities. Calcium was required for the binding of transcobalamin II to K562 cells. Brief treatment of these cells with trypsin resulted in almost total loss of surface binding activity. After removal of trypsin, surface receptors for TCII slowly reappeared, reaching pretrypsin treatment densities only after 24 hours. Reappearance of receptors was blocked by cycloheximide. TCII receptor densities on K562 and HL-60 cells correlated inversely with the concentration of cobalamin in the culture medium. This suggests that intracellular stores of cobalamin may affect the expression of transcobalamin receptors. Nonproliferating stationary-phase K562 cells had low TCII receptor densities (less than 1,200 receptors/cell). However, the density of TCII receptors increased substantially when cells were subcultured in fresh medium. Up-regulation of receptor expression coincided with increased 3H-thymidine incorporation, which preceded the resumption of cellular proliferation as measured by cell density. In the presence of cytosine arabinoside, which induces erythroid differentiation, K562 cells down-regulated expression of TCII receptors. When HL-60 cells were subcultured in fresh medium containing dimethysulfoxide to induce granulocytic differentiation, the up-regulation of TCII receptors was suppressed. This event occurred well before a diminution of 3H-thymidine incorporation and cessation of proliferation. Thus, changes in the regulation of expression of TCII receptors correlate with both the proliferative and differentiation status of cells.

Topics: Cell Division; Cell Line; Cell Membrane; Cell Transformation, Neoplastic; Cobalt Radioisotopes; Cytarabine; Dose-Response Relationship, Drug; Down-Regulation; Gene Expression; Humans; Leukemia, Erythroblastic, Acute; Leukemia, Experimental; Leukemia, Myeloid; Receptors, Cell Surface; Transcobalamins; Trypsin; Up-Regulation; Vitamin B 12

DNA synthesis time (Ts) and 3H-thymidine labelling index (TLI) of erythroblasts have been determined in 25 patients with various types of haematologic disorders using in vitro double labelling method. No remarkable differences in both Ts and TLI were noted between haematologically normal subjects and patients with increased effective erythropoiesis (haemolytic anaemias), suggesting that the cell cycle time is not principally altered under the augmented erythropoiesis. In pernicious anaemia, Ts of basophilic erythroblasts was significantly shortened and TLI was elevated above normal. Normalization of erythropoiesis by vitamin B12 was associated with a transient increase of TLI in polychromatic erythroblasts, which was interpreted to reflect prevention of intramedullary premature death of basophilic megaloblasts. Erythroleukaemia showed a markedly prolonged Ts and lowered TLI indicating the presence of cells with prolonged cell cycle time. These findings contrasted to that of pernicious anaemia despite certain morphological as well as functional similarities. In idiopathic sideroblastic anaemia, prolongation of Ts was observed to a similar extent as erythroleukaemia, while TLI remained almost normal. In 2 cases with suspected erythroleukaemia presenting an intermediate clinical picture between erythroleukaemia and sideroblastic anaemia, Ts of basophilic erythroblasts was found to be prolonged along with modestly lowered TLI.

Topics: Anemia, Pernicious; Anemia, Sideroblastic; Autoradiography; Cell Cycle; DNA; Erythroblasts; Erythrocytes; Erythropoiesis; Humans; Leukemia, Erythroblastic, Acute; Time Factors; Vitamin B 12

Report on a case of severe megaloblastic anemia in a vegetarian, associated with marked erythroleukemic blood findings probably caused by infections (bronchopneumonia, asthmatic bronchitis, urinary tract infection) and severe heart failure. Successful treatment of the above mentioned complications resulted in almost complete disappearance of pathologic cells from the blood even before vitamin B12 treatment was started. With this therapy complete recovery was achieved and the signs suspect for erythroleukemia in blood and bone marrow disappeared definitively. The case also fulfilled all the criteria of pernicious anemia (Schilling's test and determination of intrinsic factor were not done).

Topics: Aged; Anemia, Macrocytic; Anemia, Megaloblastic; Bone Marrow Examination; Digitalis Glycosides; Diuretics; Female; Folic Acid; Heart Failure; Humans; Leukemia, Erythroblastic, Acute; Obesity; Vitamin B 12; Vitamin B 12 Deficiency

Topics: Anemia, Aplastic; Anemia, Sideroblastic; Arginine; Chronic Disease; Erythroblasts; Esterases; Glycogen; Histones; Humans; Iron; Leukemia, Erythroblastic, Acute; Methyltransferases; Vitamin B 12

Topics: 5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; Anemia, Pernicious; Apoenzymes; Bone Marrow; Homocysteine; Humans; Leukemia, Erythroblastic, Acute; Methyltransferases; S-Adenosylmethionine; Tetrahydrofolates; Vitamin B 12

Topics: Anemia, Hemolytic, Autoimmune; Anemia, Pernicious; Anthraquinones; Bone Marrow; Bone Marrow Cells; Coenzyme A; Cytoplasm; Erythrocytes, Abnormal; Fluorescent Dyes; Folic Acid Deficiency; Humans; Leukemia, Erythroblastic, Acute; Megaloblasts; Microscopy, Fluorescence; NADP; Staining and Labeling; Vitamin B 12

Topics: Adolescent; Adult; Aged; Bilirubin; Blood Platelets; Bone Marrow; Bone Marrow Cells; Female; Folic Acid; Humans; Iron; Leukemia, Erythroblastic, Acute; Leukemia, Myeloid; Leukocytes; Male; Megaloblasts; Middle Aged; Polycythemia Vera; Reticulocytes; Transferrin; Vitamin B 12

Topics: Adolescent; Blood Transfusion; Cytosine; Female; Folic Acid; Humans; Leukemia, Erythroblastic, Acute; Leukemia, Myeloid, Acute; Syndrome; Vincristine; Vitamin B 12

Topics: Cytarabine; Folic Acid; Humans; Leukemia, Erythroblastic, Acute; Mercaptopurine; Methotrexate; Prednisone; Pyridoxine; Remission, Spontaneous; Vitamin B 12

Topics: Anemia; Bilirubin; Blood Transfusion; Bone Marrow; Bone Marrow Cells; Erythropoiesis; Erythropoietin; Hematocrit; Humans; Leukemia, Erythroblastic, Acute; Leukocyte Count; Male; Middle Aged; Pneumonia; Reticulocytes; Vitamin B 12

Topics: Aged; Blood Platelets; Bone Marrow Examination; Diagnosis, Differential; Erythropoiesis; Hematocrit; Hemoglobinometry; Humans; Leukemia, Erythroblastic, Acute; Leukocyte Count; Male; Mitosis; Myelography; Vitamin B 12

A patient with the apparently unique combination of pernicious anaemia and acute erythraemic myelosis is described. The implications of some of the unusual features together with the difficulties encountered in diagnosis and treatment are discussed.

Topics: Aged; Anemia, Pernicious; Bone Marrow Cells; Bone Marrow Examination; Female; Humans; Leukemia, Erythroblastic, Acute; Vitamin B 12

Topics: Animals; Chick Embryo; Cobalt; Erythropoietin; Leukemia, Erythroblastic, Acute; Nandrolone; Poultry; Prednisone; Vitamin B 12

Topics: Absorption; Anemia; Anemia, Pernicious; Celiac Disease; Cobalt Isotopes; Cobamides; Coenzymes; Drug Therapy; Erythrocytes; Humans; Intestine, Small; Intestines; Intrinsic Factor; Leukemia, Erythroblastic, Acute; Leukemia, Myeloid; Liver; Male; Metabolism; Reticulocytes; Schilling Test; Urine; Vitamin B 12

Topics: Humans; Leukemia, Erythroblastic, Acute; Vitamin B 12; Vitamin B 12 Deficiency

Topics: Anemia; Anemia, Myelophthisic; Blood Cells; Corrinoids; Hematinics; Humans; Leukemia, Erythroblastic, Acute; Vitamin B 12