The effect of various cytotoxic agents on the erythroid precursors in rat bone marrow

Use of multiparameter analysis to quantitate hematological damage from exposure to a chemical (ethylene oxide)

This study was designed to test the value of a multiparameter approach in evaluating perturbations in bone marrow and peripheral blood elements of mice exposed to ethylene oxide (EtO). Mice exposed to 255 ppm EtO for 5 h/d were removed for analysis after 1, 2, 8, and 14 d (sequential exposure) and 4, 6, 8, and 10 wk (5 d/wk). Prior to sacrifice, blood was removed from the orbital sinus for blood cell counts, hemoglobin determination, and hematocrit. A blood film was made for differential leukocyte counts. Bone marrow was flushed from femurs and tibias and counted, and aliquot were used for stem-cell assay (CFU-S) or flow cytometry (FCM) analysis. One aliquot of marrow was stained with propidium iodide for cell-cycle analysis and another was reacted with fluorescein-conjugated monoclonal antibody for B-cell analysis. The preparations were analyzed for forward and 90 degrees scatter and fluorescence on an Ortho 50H cytofluorograph. Perturbations of peripheral leukocytes occurred after one exposure. After multiple exposures, hematocrit, red-cell number, and hemoglobin were generally depressed, with transient compensatory bursts, and bone marrow cellularity and CFU-S were below normal. However, white-cell numbers fluctuated dramatically during the exposure period. There was a shift in differential toward granulocytes, at times resulting in severely depressed numbers of lymphocytes in the peripheral blood. The FCM analysis showed an early depletion of granulocytes in the bone marrow followed by replacement and a relative lymphocyte deficit, especially pronounced at 10 wk. The B-cell changes reflected general lymphocyte perturbations. Shifts in numbers of cells in S and G/M were observed, consistent with a moderate bone marrow response to cell loss.

Hemopoietic stem cell heterogeneity: use of cell cycle-specific drugs to look for age-associated alterations

Hemopoietic tissue is vulnerable to perturbations, and data show that it is an appropriate tissue in which to look for age-associated alterations. This tissue has a high regenerative capacity, is composed of a heterogeneous population of stem cells that are capable of self renewal or differentiation, or both, and is sustained by a pool of resting cells. The heterogeneity of bone marrow has made characterization of the cellular elements difficult. Techniques commonly used to identify and quantify the various maturation levels of hemopoietic stem cells and the limitations of these techniques are discussed. Most techniques used to assay age-associated changes in bone marrow have not differentiated between specific cellular alterations or shifts in the distribution of the cellular elements. In particular, it has been difficult to determine the stability of the non-dividing stem cell because of the low incidence of this cell (6 per 1000) and the lack of a specific assay for this important cell type. The use of cell cycle-specific drugs has provided quantitative information on specific subpopulations of hemopoietic stem cells and seems to be the most promising approach towards determining qualitative and quantitative differences in the hemopoietic stem cells of young and old individuals.

Proliferation rate of haemopoietic stem cells after damage by several cytostatic agents

The haemopoietic tissue of mice was damaged by different cell-cycle-stage specific and cell-cycle-stage non-specific cytostatic agents. The proliferation rate among the surviving pluripotential stem cells, i.e. those cells forming colonies in spleens of lethally irradiated mice (CFUs), was then investigated. The results suggest that, at least in the CFUs population, the cells which synthesize DNA in the S phase of the cell cycle inhibit the entry of the non-proliferating GO cells into cell cycle. This evidence was based on the ability of three cytostatic agents, hydroxyurea, cytosine arabinoside and methotrexate, which are toxic specifically to the S phase cells to increase the proliferation in the CFUs population. This increase was quite out of proportion to the small amount of damage they caused to the population. Colchicine, which kills cells in mitosis, and ionizing irradiation, damaging cells in all stages, proved to be much weaker stimulators of proliferation. It has been suggested that a mechanism for the control of cellular proliferation might be based on the negative feedback in the cell cycle. In this feedback control loop the cells which are preparing for cell division in the S phase of the cell cycle inhibit the entry of the non-proliferating GO cells into cell cycle.

Study of the effect of hydroxyurea on the erythropoietin-sensitive cells

The response of polycythaemic mice to a standard dose of erythropoietin has been measured at various time intervals after single or repeated injections of hydroxyurea. The results exclude S phase of the cell cycle as the period responsive to erythropoietin. They suggest the existence of feedback mechanisms within the cell cycle, operating at the G1--S boundary and within the G1 phase. Hydroxyurea given to polycythaemic mice at various time intervals after erythropoietin induced characteristic changes in the response. These changes can be explained if both gradual transit of differentiated cells into the DNA synthesis (S phase) and changes in amount of the erythropoietin sensitive cells caused by the feedback mechanisms operating in the cell cycle are considered.

Experimental Study of the Relationships between Activation of Erythropoiesis and Hematotoxicity of Some Antitumoral Agents

The changes in the blood toxicity of some antitumoral chemotherapeutic agents in the presence of erythropoiesis activation by bleeding are evaluated. The general toxicity seems to be unaffected but the damage to erythropoiesis proved, in absolute terms, to be more severe in the bled animals. The recovery of hematopoiesis was slower after some drugs than others. These results are discussed in the light of present knowledge of hematopoietic kinetics and of the relationships between antiblastic drugs and stamina] hematopoietic compartments.