Regulation of erythropoiesis. 18. The effect of vincristine and erythropoietin on bone marrow

Vincristine-induced anemia in hereditary spherocytosis

Vincristine, a vinca alkaloid, is widely used in many hematologic disorders and pediatric cancers, and acts by binding to the tubulin protein, to inhibit effective cell division. Vincristine-induced anemia has been observed, but its mechanism is not well understood. We describe a case involving serious vincristine-induced anemia in a patient with congenital spherocytosis and provide the explanation to the underlying mechanism. This report demonstrates that vincristine administration to patients with a red cell disorder may require additional clinical interventions to compensate for the vincristine-induced anemia.

Impact statement

Therapy with vincristine (VCR), a vinca alkaloid, is widely used in many hematologic disorders and pediatric cancers, and acts by binding to the tubulin protein, to inhibit effective cell division. Our paper indicates that treatment of patients with a red cell disorder may require additional clinical interventions to compensate for the VCR-induced anemia. Careful evaluation of other hematologic disorders is important in using a well-known oncology treatment. Whereas extreme concentrations of VCR were shown to alter red cell viability, data did not show negative effects in patients treated. Our data show that under conditions of increased hematopoiesis, hemoglobin in the circulation drops rapidly requiring transfusion. VCR administration to patients with a red cell disorder may require additional clinical interventions to compensate for the VCR-induced anemia.

Acute leukaemia: development, remission/relapse pattern, relationship between normal and leukaemic haemopoiesis, and the 'sleeper-to-feeder' stem cell hypothesis

Attention has been focused on two problems of acute leukaemia: (1) the origin of normal-appearing haemopoietic cells during relapse, and (2) the inverse relationship between leukaemic blast cell proliferation and useful haemopoietic cell production. The available evidence suggests that the normal-appearing cells during relapse may not all be remnants of normal haemopoiesis but may at least in part be derived from leukaemic cells. Although a differentiation defect is a major characteristic of acute leukaemia, it seems as if this defect is not absolute: some cells may succeed in differentiating more or less normally in spite of their descent from a leukaemic stem cell. Acute leukaemia is usually considered to be a primary white cell disorder which indirectly affects the other haemopoietic cell lines. It appears more likely, however, that acute leukaemia, at least the myeloid type, is a disorder of a stem cell common to granulocytopoiesis, erythropoiesis, and probably thrombocytopoiesis. Most descendants from the diseased stem cell fail to differentiate and remain at the blast cell level where they proliferate for some time; however, at a certain point proliferation ceases and the cells ultimately die. Another fraction of the progeny of the leukaemic stem cells may differentiate to some extent and may give rise to functionally useful cells. This is analogous to chronic myeloid leukaemia. The mechanism by which useful haemopoiesis apparently is suppressed in the presence of leukaemic blast cells has remained enigmatic so far. Previously suggested explanations which all assume some kind of cell-cell interaction by which normal haemopoietic cells succumb have neither been proved nor disproved. In this chapter, a new hypothesis is presented. It is assumed that some normal haemopoietic stem cells enter a dormant state at various distances in lineage from the fertilized ovum ('sleepers'). Another fraction of haemopoietic stem cells ('feeders') are actively proliferating and serve to feed the differentiating haemopoietic cell lines and to maintain the 'feeder' pool. When the 'feeder' pool is exhausted, a 'sleeper' cell is activated and sets up a new 'feeder' clone. Otherwise, 'sleepers' are protected against acting as 'feeders' in order to keep 'sleeper' divisions at a minimum and thus preserve their genetic information as intact as possible. It is suggested that the leukaemic event initially takes place in one or a few 'sleepers'. If the leukaemic 'sleeper' never succeeds in setting up a 'feeder' clone, clinical leukaemia will not develop. Clinical leukaemia will result if a leukaemic 'sleeper' establishes a leukaemic 'feeder' pool.(ABSTRACT TRUNCATED AT 400 WORDS)

A mathematical model of iron metabolism

A mathematical model of iron metabolism is presented. It comprises the following iron pools within the body: transferrin-bound iron in the plasma, iron in circulating red cells and their bone marrow precursors, iron in mucosal, parenchymal and reticuloendothelial cells. The control exerted by a hormone, called erythropoietin, on bone marrow utilization of iron for hemoglobin synthesis is taken into account. The model so obtained consists of a system of functional differential equations of retarded type. Most model parameters can be estimated from radiotracer experiments, others can be measured and numerical values can be assigned to the remaining ones making few reasonable assumptions according to the available physiological knowledge. Iron metabolism behavior under different therapeutical treatments was stimulated. Model predictions were compared to experimental data collected in clinical routine.

Desacetyl vinblastine amide sulfate induced ineffective erythropoiesis

Ineffective erythropoiesis occurred during desacetyl vinblastine amide sulfate (VDS) therapy of a patient with metastatic Ewing's sarcoma. The peripheral blood was characterized by anisocytosis, poikilocytosis and reticulocytopenia. Bone marrow showed megaloblastic red cell hyperplasia with nuclear fragmentation, binuclearity and abnormal metaphases. Radioiron incorporation into red cells was markedly decreased. Electron microscopy showed red cell surface changes previously called ropalocytosis. Normal erythropoiesis promptly resumed when VDS treatment was withheld. Although less common than leukopenia, red cell abnormalities are part of the spectrum of vinca alkaloid toxicity.

Serum thrombopoietic activity following administration of vinblastine

A possible role of humoral factors in the pathogenesis of vinblastine-induced thrombocytosis was examined. The thrombopoietic activity in serum of experimental animals was tested for its ability to stimulate the incorporation of 75-Se-selonemethionine into platelets of thrombocythaemic mice. The administration of low doses (0.1--0.5 mg/kg body wt.) of vinblastine to rabbits caused a significant increase in serum thrombopoietic activity. Higher doses of vinblastine (1--5 mg/kg body wt.) also increased the serum thrombopoietic activity, but this increase was preceded by a transient drop in the platelet count of peripheral blood. This thrombocytopenia could have been a stimulus for an increase in thrombopoietic activity, through a compensatory feedback mechanism. The vinblastine-induced increase in thrombopoietic activity was abolished by bilateral nephrectomy but not by bilateral ureteral ligation. These data suggest that kidney tissue may be a major source of the serum thrombopoietic factors.

Erythroid differentiation of fetal, newborn and adult haemopoietic stem cells

Erythroid regeneration was studied in lethally irradiated mice given transplants containing equivalent numbers of haemopoietic stem cells (i.e. CFU) from fetal liver, neonatal marrow or adult marrow. Adult marrow was taken from normal control mice, whose CFU for the most part were not in active cell cycle, as well as from phenylhydrazine-treated groups whose CFU were in similar state of proliferation (i.e. approximately 40-50% in DNA SYNTHESIS) AS THOSE DERIVED FROM FETAL LIVER AND NEONATAL MARROW. Splenic and femoral radioiron (59Fe) incorporation were measured at intervals after transplantation and were found to begin earliest in mice given fetal liver, then in animals given neonatal marrow and latest in recipients of adult marrow. Peripheral reticulocytes showed a similar pattern of recovery. The data reported herein suggest that the differences in erythroid regeneration evoked by transplants of fetal liver, neonatal marrow or adult marrow, are not solely attributed to the degree of proliferation in the pluripotential stem cell compartment. These data may, however, suggest a shorter doubling time for cells comprising the fetal and newborn committed erythroid compartments.

Effects of vincristine on normal and stimulated megakaryocytopoiesis in the rat

Vincristine was given to rats in which thrombocytopoiesis was either normal or acutely or chronically stimulated by injections of heterologous antiplatelet serum. A single dose of 0.3 mg/kg was given intravenously. The drug produced an early and a delayed megakaryocytopenia suggesting that it was toxic to differentiated megakaryocytes as well as to proliferating stem cells. The results support the hypothesis that vincristine-induced thrombocytosis may be due to homeostatic adjustments which, in turn, are activated as a result of drug-induced cytotoxicity.