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Stimulation tests for the bone marrow neutrophil pool in malignancies.

It has been known for decades that blood neutrophilia occurs after the administration of etiocholanolone, adrenocortical steroids, and endotoxins. Neutrophil leukocytosis in general may be due to several mechanisms such as increased stimulation of the myelopoiesis, increased release from the marrow, a shift from the marginated to the circulating pool (demargination), prolongation in the peripheral half-life, and decreased migration of neutrophils from the blood to the tissue. However, the principal cause of the neutrocytosis for each of the above mentioned agents is increased release of neutrophils from the bone marrow reserves. Since a sufficient reserve capacity is a prerequisite for optimal defenses against infections, the marrow response has been used to estimate the dose of chemotherapy expected to be tolerated without life-threatening neutropenia. However, none of the above "test substances" have gained widespread use due to adverse reactions or undesirable effects on neutrophil function. Recent progress in biotechnology has developed recombinant human (rh) hematopoietic growth factors ready for clinical use. Marrow myelopoiesis is stimulated by granulocyte colony-stimulating factor (rhG-CSF) and granulocyte-macrophage CSF (rhGM-CSF). The immediate effect, however, is mobilization of mature neutrophil granulocytes to the blood. Bone marrow cellularity seems to influence the neutrophil number mobilized during 24 hours by one subcutaneous injection of either rhG-CSF or rhGM-CSF. A recent pilot study has suggested such a "24 hour stimulation test" to predict severe neutropenia following cyclic chemotherapy. This concept is illustrated by two case reports. The "stimulation test" suggests that we may devise strategies to define patient subsets which may benefit from prophylactic growth factor administration during cyclic chemotherapy.

Bone Marrow↗

In vivo toxicity of 3'-azido-3'-deoxythymidine (AZT) on CBA/Ca mice.

CBA/Ca male mice were given 3'-azido-3'-deoxythymidine (AZT) in drinking water (1 mg/ml) for up to 7 weeks. Water consumption and body weight decreased significantly. Neutropenia and lymphopenia were observed during and after exposure. Significant macrocytic anemia developed and disappeared as a function of red cell life span after stopping AZT intake. A microthrombocytosis was seen. Bone marrow cellularity and spleen colony-forming unit (CFU-s) content fell, but recovered completely and quickly after terminating AZT intake. Hemopoietic stem cell function measured by 2 different methods of rescuing fatally irradiated mice was normal 4 weeks after AZT exposure, suggesting that AZT treatment does not induce a long-lasting effect in genetic control of mitotic potential of stem cells. This is in marked contrast to exposure of CBA/Ca mice to benzene and ionizing radiation.

Administration, Oral↗

A direct assay of granulocytic repopulating ability.

A direct method of assay of the 'granulocytic repopulating ability' (GRA) of bone marrow in normal or treated mice, which utilizes determinations of total bone marrow cellularity and peroxidase positive cells, is described. Ten days after transplantation of normal femoral marrow, the total number of marrow granulocytes in the recipients is proportional to the marrow dose in the range 0.01 to 0.03 of a femur. Above 0.01 femur the proportion of granulocytes is constant at about 60% so there is a high correlation between total cellularity and total granulocytes. Assay of erythroid repopulating ability can be performed in the same animals. Using the GRA assay, the results for the dose response curve for cyclophosphamide, and the relationship of GRA to erythroid repopulating ability (ERA) and spleen colony forming cells, are similar to those obtained using the endotoxin technique. The simplicity of the GRA technique enhances the feasibility of multiple simultaneous hematopoietic precursor cell assays.

Animals↗

Modulation of myelopoiesis by CSF or CSF-inducing biological response modifiers.

We have compared the effects on number and function of bone marrow progenitors and peripheral effector cells of the myelomonocytic lineage of treatment with the 2-cyanaziridine compounds Azimexone and BM 41.332 to those of maleic anhydride divinyl ether copolymer (MVE-2) or granulocyte-macrophage colony stimulation factor (GM-CSF). Within a few hours after i.p. injection of either Azimexone or BM 41.332, there was a dose-dependent increase in serum CSF levels, CSF secretion by mononuclear bone marrow cells (BMC) and macrophages (M phi), which was followed by an increase in granulocyte-M phi committed stem cells (GM-CFU-C), nucleated BMC, and peripheral blood leukocytes. Optimal effects occurred 3 days after 50 mg/kg Azimexone or 25 mg/kg BM 41.332. Three i.p. injections of 50 mg/kg Azimexone into mice pretreated with cyclophosphamide (CY) (150 mg/kg) were able to significantly restore suppressed bone marrow cellularity (GM-CFU-C and nucleated BMC). Azimexone also increased the number of peripheral M phi in normal or CY-treated mice, without inducing detectable tumoricidal activity. These M phi, however, retained their capacity to become fully activated (cytotoxic) by appropriate activation signals such as IFN or LPS. Analogous to the 2-cyanaziridines. MVE-2 (at 25 mg/kg) had similar stimulatory effects on myeloid functions in normal mice. MVE-2 induced, in addition, a significant augmentation of cytoxicity by both M phi and NK cells. In contrast, single or multiple injections of semipurified GM-CSF into normal mice (1000 U or 5000 U per mouse) failed to detectably stimulate myelopoietic growth and differentiation. 2-cyanaziridine compounds thus offer the potential of selectively augmenting growth and differentiation of myelomonocytic cells in normal and bone marrow-depressed mice without appreciably affecting their immunological status.

Adjuvants, Immunologic↗

An interaction of benzene metabolites reproduces the myelotoxicity observed with benzene exposure.

Benzene-induced myelotoxicity can be reproduced by the coadministration of two principal metabolites, phenol and hydroquinone. Coadministration of phenol (75 mg/kg) and hydroquinone (25-75 mg/kg) twice daily to B6C3F1 mice for 12 days resulted in a significant loss in bone marrow cellularity in a manner exhibiting a dose-response. One explanation for this potentiation is that phenol stimulates the peroxidase-dependent metabolism of hydroquinone. Addition of phenol to incubations containing horseradish peroxidase, H2O2, and hydroquinone resulted in a stimulation of both hydroquinone removal and benzoquinone formation. Stimulation occurred with phenol as low as 100 microM and with very low concentrations of horseradish peroxidase. When boiled rat liver protein was added to identical incubations containing [14C]hydroquinone, the level of radioactivity recovered as protein bound increased by 37% when phenol was added. Similar results were observed when [14C]hydroquinone was incubated in the presence of activated human leukocytes. Hydroquinone binding was increased by approximately 70% in the presence of phenol. Phenol-induced stimulation of hydroquinone metabolism and benzoquinone formation represents a likely explanation for the bone marrow suppression associated with benzene toxicity.

Animals↗

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)-induced immunotoxicity.

The selective toxicity of TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) for the thymus, consisting primarily of immature T-cells, led us to search for an analogous selective toxicity for the immature B-lymphocytes in the bone marrow. In the dose-response study C57B1/6 male mice were injected with either vehicle alone (corn oil), 30, 60, or 120 micrograms/kg of TCDD i.p. The mice were killed by cervical dislocation 7 days later. In the time-response study, mice were injected with either saline or 120 micrograms/kg i.p. TCDD, 3, 7, 14, or 21 days before killing. In both studies, the following were analyzed: change in body weight, thymus weight, spleen and bone marrow cellularity, and spleen and marrow B-lymphocyte function, measured using the in vitro B-lymphocyte colony forming unit in culture assay, with the mitogen lipopolysaccharide (LPS) from Salmonella typhosa, and the in vitro plaque forming cell assay, with the thymus independent antigen, TNP-LPS. In the dose-response study there was a reduction in thymic weight, spleen B-cell functional response (per spleen), and bone marrow B-cell functional response to 14%, 35-54%, and 20-32% of control, respectively, at a dosage of 120 micrograms/kg. In the time-response study, thymic weight and bone marrow B-cell functional response (per femur) were reduced to 6% and 18% of control, respectively, at day 21. The results indicate that TCDD was selectively more toxic to the immature B-cells in the bone marrow than the more mature B-cells in the spleen. This immunotoxicity was dose-dependent.

Animals↗

The immunosuppressant rapamycin blocks in vitro responses to hematopoietic cytokines and inhibits recovering but not steady-state hematopoiesis in vivo.

The immunosuppressive drug rapamycin suppresses T-cell activation by impairing the T-cell response to lymphokines such as interleukin-2 (IL-2) and interleukin-4 (IL-4). In addition, rapamycin blocks the proliferative response of cell lines to a variety of hematopoietic growth factors, including interleukin-3 (IL-3), interleukin-6 (IL-6), granulocyte-colony stimulating factor (G-CSF), granulocyte macrophage-colony stimulating factor (GM-CSF), and kit ligand (KL), suggesting that it should be a strong inhibitor of hematopoiesis. In this report, we studied the effects of rapamycin on different hematopoietic cell populations in vitro and in vivo. In vitro, rapamycin inhibited the proliferation of primary bone marrow cells induced by IL-3, GM-CSF, KL, or a complex mixture of factors present in cell-conditioned media. Rapamycin also inhibited the multiplication of colony-forming cells in suspension cultures containing IL-3 plus interleukin-1 (IL-1) or interleukin-11 (IL-11) plus KL. In vivo, treatment for 10 to 28 days with high doses of rapamycin (50 mg/kg/d, orally) had no effect on myelopoiesis in normal mice, as measured by bone marrow cellularity, proliferative capacity, and number of colony-forming progenitors. In contrast, the same treatment strongly suppressed the hematopoietic recovery normally seen 10 days after an injection of 5-fluorouracil (5-FU; 150 mg/kg, intravenously [i.v.]). Thus, rapamycin may be detrimental in myelocompromised individuals. In addition, the results suggest that the rapamycin-sensitive cytokine-driven pathways are essential for hematopoietic recovery after myelodepression, but not for steady-state hematopoiesis.

Animals↗

Hematopoietic effects of benzene inhalation assessed by murine long-term bone marrow culture.

The strong and long-lasting hematotoxic effect after benzene exposure in vivo (300 ppm, 6 hours/day, 5 days/week for 2 weeks) was assessed in mice with bone marrow cells grown in long-term bone marrow culture (LTBMC). Bone marrow cultures initiated 1 day after the last benzene exposure did not produce adequate numbers of hematopoietic cells over 3 weeks and, in most cases, no erythroid or myeloid clonogenic cells could be recovered. The adherent cell layer of these cultures had a lower capacity for supporting in vitro hematopoiesis after the second seeding with normal bone marrow cells compared with control cultures. Two weeks after the last benzene exposure, body weight, hematocrit, bone marrow cellularity, and committed hematopoietic progenitor content (BFU-E and CFU-GM) were regenerated to normal or subnormal values, whereas hematopoiesis in LTBMC was very poor. Over 8 weeks, little or no significant committed progenitor production was observed. Treatment of mice exposed to benzene with hemin (three doses of 3 micrograms/gm body wt, iv, over 2-week for a total dose 9 micrograms/gm) partially overcame the toxic effect of benzene on the hematopoietic system as measured by the LTBMC method. Cultures from mice treated with hemin had modest recovery of BFU-E and CFU-GM clonogenic potential after 5 to 6 weeks in LTBMC. In contrast, little or no recovery was obtained for the adherent cell layer clonogenic capacity, even after hemin treatment. These results clearly indicate a strong, long-lasting toxic effect on the bone marrow stroma and a limited recovery of hematopoietic potential by clonogenic cells of the nonadherent population after in vivo hemin treatment.

Animals↗

Hematopoietic effects of benzene inhalation assessed by long-term bone marrow culture.

The strong and long-lasting hematotoxic effect after benzene exposure in vivo (300 ppm, 6 hr/day, 5 days/week for 2 weeks) was assessed in mice with bone marrow cells grown in long-term bone marrow culture (LTBMC). Bone marrow cultures initiated 1 day after the last benzene exposure did not produce adequate numbers of hematopoietic cells over 3 weeks, and, in most cases, no erythroid or myeloid clonogenic cells could be recovered. The adherent cell layer of these cultures had a lowered capacity for supporting in vitro hematopoiesis after the second seeding with normal bone marrow cells compared with control cultures. Two weeks after the last benzene exposure, body weight, hematocrit, bone marrow cellularity, and committed hematopoietic progenitor content (BFU-E and CFU-GM) were regenerated to normal or subnormal values, whereas hematopoiesis in LTBMC was very poor. Over 8 weeks, little or no significant committed progenitor production was observed. Treatment of mice exposed to benzene with hemin (three doses of 3 micrograms/g bw i.v. over 2 weeks for a total dose of 9 micrograms/g) partially overcame the toxic effect of benzene on the hematopoietic system as measured by the LTBMC method. Cultures from mice treated with hemin had a modest recovery of BFU-E and CFU-GM clonogenic potential after 5 to 6 weeks in LTBMC. In contrast, little or no recovery was obtained for the adherent cell layer clonogenic capacity, even after hemin treatment. These results clearly indicate a strong, long-lasting toxic effect on the bone marrow stroma and a limited recovery of hematopoietic potential by clonogenic cells of the nonadherent population after in vivo hemin treatment.

Administration, Inhalation↗

The different responses of the female mouse thymus to estrogen after treatment of neonatal, prepubertal, and adult animals.

Contrary to the common description of estrogen-induced thymus atrophy we have observed a thymus enlargement after treatment of neonatal female mice with estrogen. We now describe an age-dependent difference in the estrogen response (enlargement, atrophy) as well as mechanisms relevant to the response. Groups of female NMRI mice were treated with estrogen (diethylstilbestrol, DES) at different 5-day periods in prepubertal (day 1-5, day 6-10, day 30-34) or postpubertal life (days 48-52). All the treatment groups showed a reduced thymus weight 4 days after the last treatment but later responses differed. Neonatal DES treatment resulted in an ovary-independent thymus enlargement 8 weeks after the treatment when the cortical part was relatively larger than in controls; treatment on days 30-34 was followed by a rebound type of regeneration; the acute weight reduction after treatment on days 48-52 was normalized 16 days later. Neonatal DES treatment transiently depressed the number of thymic S phase cells 4 days after the treatment while apoptosis was similar in controls and DES females. The estrogen receptor pattern was not affected by DES. The number of white blood cells was temporarily depressed while the bone marrow cellularity was still reduced in 8-week-old females. Neonatal treatment with an LH-releasing hormone antagonist reduced thymus weight at 8 weeks but had no effect on the DES-induced enlargement. The delayed-type hypersensitivity response developed differently in controls and DES females. The thymus enlargement after neonatal estrogen treatment could be the result of an increased immigration of precursor cells into the thymus and/or a defect maturation/emigration mechanism. Further studies on different cell subsets are necessary to explain the mechanism behind the thymus enlargement.

Aging↗

Hematopoietic and hematologic properties of bestatin in normal and cyclophosphamide myelosuppressed mice.

Bestatin is a potent inhibitor of aminopeptidase, an enzyme found in abundance in the membrane of monocytes and macrophages. Following binding of bestatin to cells in the histiocytic lineage, the production of colony stimulating activity is upregulated (both in vitro and in vivo) with subsequent increases in hematopoietic and hematologic parameters. We report that the frequency and absolute numbers of CFU-GM as well as entry of CFU-GM into S phase (a measure of progenitor cell activity) is upregulated by treatment of animals with bestatin. This results in an increase in bone marrow cellularity in cyclophosphamide suppressed mice and an increase in the absolute neutrophil count in normal and suppressed mice. The therapeutic application of this hematopoietic modulator has been demonstrated in combination cyclophosphamide and bestatin therapeutic protocols. Because this indication for bestatin has only recently been recognized, few clinical studies have been undertaken utilizing appropriate surrogates of hematopoietic activity. However, preliminary clinical evidence of hematopoietic activity by this non-toxic dipeptide, as reviewed here, suggests that this may be an appropriate strategy for the treatment of myelosuppressed patients.

Aminopeptidases↗

Abnormal platelet adhesion on abdominal vessels in asymptomatic patients with paroxysmal nocturnal hemoglobinuria.

Platelet kinetic studies were performed in eight patients with paroxysmal nocturnal hemoglobinuria (PNH) but without symptoms or signs related to thrombosis. Indium-111 tropolonate labeled autologous platelets were used to determine mean platelet life and platelet production rate; total body images were also acquired. Three of seven patients with a thrombocytopenia showed a shortened mean platelet life, and the other five demonstrated a (nearly) normal platelet survival. Four of the seven patients with thrombocytopenia showed a decreased platelet production rate, but bone marrow cellularity was normo- to hypercellular. These observations suggest ineffective thrombopoiesis in 57% of the patients with PNH and thrombocytopenia. Total body imaging was performed during the platelet kinetic study in order to study organ uptake. Imaging of the abdominal vessels was demonstrated in all patients, suggesting enhanced adherence of platelets to the endothelium in patients with PNH. Since thrombosis of especially the abdominal vessels is a major cause of morbidity and mortality, the use of antithrombotic drugs might be considered despite the absence of abdominal complaints.

Abdomen↗

Efficacy and clinical cross-resistance of a new combination therapy (AMSA/VP16) in previously treated patients with acute nonlymphocytic leukemia.

We investigated the tolerance, efficacy, and clinical cross-resistance of a new combination chemotherapy in 38 patients with previously treated acute myeloblastic leukemia (AML). It consisted of 120 mg2/d 4'(9-acridinylamino) methanesulfon-m-Anisidide (m-AMSA) in a one-hour infusion and 80 mg/m2/d etoposide (VP-16) in a 24-hour infusion, both administered for 5 days. The first 27 patients also received vinblastine, 6 mg/m2 on day 8, but this therapy was discontinued because of intestinal complications. Thirteen of 23 patients (56%) at first or subsequent relapse and five of 15 patients (33%) who were primarily resistant to an anthracycline/cytarabine combination achieved a complete response (CR) (hemoglobin level not taken into account) with a median CR duration of 5 months and 2 months, respectively. The response rate was as high as 63% for patients at first or second relapse whether the remission was maintained or not. The median times to recovery of normal bone marrow cellularity, of blood granulocyte counts greater than 500/microL, and of platelets greater than 20,000/microL were 34, 27, and 22 days, respectively. Marked but reversible gastrointestinal toxicity was observed in 24% of the patients, and two patients died of infection during induction. The one-hour AMSA/continuous VP-16 combination is effective for patients with relapsing AML and shows no cross-resistance in a proportion of patients refractory to the standard anthracycline-cytarabine combination.

Adolescent↗

Effects of recombinant human interleukin-3 in aplastic anemia.

In a phase I/II study, nine patients with aplastic anemia were treated with recombinant human interleukin-3 (rhIL-3) to assess the toxicity and biologic effects of this multipotential hematopoietic growth factor. Doses ranging from 250 micrograms/m2 to 500 micrograms/m2 were administered as subcutaneous bolus injections daily for 15 days. An increase in platelet counts from 1,000/microL to 31,000/microL was induced by rhIL-3 in one patient, and an increase in reticulocyte counts by more than 10,000/microL in four patients. The blood leukocyte counts temporarily increased in eight patients 1.5- to 3.3-fold (median, 1.8-fold), mainly due to an increase in the number of neutrophils, eosinophils, lymphocytes, and monocytes. In two patients, bone marrow cellularity increased from 7% to 33% and from 10% to 80%, respectively, but without resulting in a substantial improvement of peripheral blood counts. Mild side effects (headache and flushing) were observed in some patients, while low-grade fever occurred in all patients. Transient thrombocytopenia necessitating discontinuation of rhIL-3 treatment occurred in one patient. In conclusion, rhIL-3 can stimulate hematopoiesis in patients with aplastic anemia; however, no lasting effects were obtained.

Adolescent↗

Studies on optimal dose and administration schedule of a hematopoietic stimulatory beta-(1,4)-linked mannan.

Several complex carbohydrates have been found to significantly stimulate hematopoiesis. CARN 750, a polydispersed beta-(1,4)-linked acetylated mannan isolated from the Aloe vera plant, has been shown to have activity in wound repair, to function as a antineoplastic, and to activate macrophages. We report, herein, the hematoaugmenting properties of CARN 750 and its optimal dose and timing of administration in an animal model of irradiation-induced myelosuppression. We observed that subcutaneous injections of 1 mg/animal of CARN 750 had equal or greater stimulatory activity for white blood cell (WBC) counts and spleen cellularity as well as on the absolute numbers of neutrophils, lymphocytes, monocytes and platelets than did higher or lower doses of CARN 750 or an optimal dose of granulocyte-colony stimulating factor (G-CSF). Hematopoietic progenitors, measured as interleukin-3-supported colony forming units-culture (CFU-C) and high proliferative potential colony-forming cells (HPP-CFC) assays, were similarly increased by CARN 750 in the spleen but not in the bone marrow. The frequency of splenic HPP-CFCs and absolute number of splenic HPP-CFCs and CFU-Cs were optimally increased by 1 mg/animal of CARN 750. In contrast, bone marrow cellularity, frequency and absolute number of HPP-CFCs and CFU-Cs had as a dosage optimum 2 mg/animal of CARN 750. These parameters were similarly increased by G-CSF. In studies to determine the optimal protocol for the administration of CARN 750 we found that the hematopoietic activity of CARN 750 increased with the frequency of administration. The greatest activity in myelosuppressed mice was observed for all hematopoietic parameters except the platelet number in mice receiving daily administration of 1 mg/animal of CARN 750 with activity equal to or greater than G-CSF.

Animals↗

Enhanced bone formation in lipodystrophic PPARgamma(hyp/hyp) mice relocates haematopoiesis to the spleen.

The peroxisome proliferator-activated receptor gamma (PPARgamma) controls adipogenesis and metabolism. We demonstrate here that the absence of PPARgamma in fat has potent osteogenic activities, which affect haematopoiesis. The congenital absence of PPARgamma in fat of lipodystrophic PPARgamma(hyp/hyp) mice, strongly enhanced bone mass and consequentially reduced the bone-marrow cavity. Consistent with this, PPARgamma(hyp/hyp) mice had a significant decrease in bone marrow cellularity and resorted to extramedullary haematopoiesis in the spleen to maintain haematopoiesis. Our data indicate that antagonizing PPARgamma activity in fat could be an effective way to combat osteoporosis and suggest that haematopoietic function should be scrutinized in lipodystrophic subjects.

Animals↗

Immune suppression therapy in aplastic anemia: influencing factors on response and survival.

OBJECTIVES: Immune suppression (IS) therapy has provided another opportunity of cure or improvement in the aplastic anemia patients who cannot receive bone marrow transplantation due to many causes. There are a few reports regarding the factors that affect response, survival and prognosis after IS therapy, including antilymphocyte globulin (ALG) in aplastic anemia. Therefore, we analysed our experience to determine the prognostic factors. METHODS: Statistically analysed were 172 patients, from April 1982 to July 1992, who were diagnosed as severe aplastic anemia and treated with IS therapy, including ALG, at Catholic University Medical College, St. Mary's Hospital. RESULTS: Among 172 severe aplastic anemia (SAA) patients who entered the study from April 1982 to July 1992, 144 patients were analysed for response and 122 patient for survival. 58.4% (84/144) responded after the first course of IS therapy. Among those who did not respond on the first course an additional 44% (11/25) responded after the second course of IS therapy. Prognostic factors that might affect the response to the treatment and survival were analysed. In a univariate analysis of patients with no previous history of treatment before is therapy, and a shorter interval between diagnosis and treatment, higher hemoglobin levels before IS therapy, and higher granulocyte counts and combined use use of cyclosporin A(CSA) were positively associated with response (p < 0.05). The combined use of CSA during IS therapy, younger age, lower monthly requirement of platelets transfusion before IS therapy, higher leukocyte counts, higher percent of polymorphonuclear leukocytes, lower percent of lymphocyte, higher bone marrow cellularity and response were positively associated with survival (p < 0.05). In a multivariate analysis, shorter interval between diagnosis and treatment, no combined use of hemopoietic stimulants, such as androgen, and lesser total amount of transfusion were positively associated with Response (p < 0.05). Higher leukocyte counts before IS therapy and the combined use of CSA during IS therapy were significantly associated with longer survival (p < 0.05). Patients with complete or partial response had excellent prognosis (96.7%-100% of 5 year survival rates). In contrast, patients with no response after IS therapy had 45.1% of 5 year survival rates. CONCLUSIONS: With these results from the retrospective study of IS therapy, we find many valuable factors that have an influence on response or survival. IS therapy improves the survival of responded patients with SAA, and we confirmed that IS therapy is an important therapeutic tool for the SAA patients who are not feasible candidates for bone marrow transplantation.

Adolescent↗

Rosiglitazone-induced protection against myelotoxicity produced by 5-fluorouracil.

Insulin promotes survival of haemopoietic progenitors. We investigated if rosiglitazone, an insulin sensitizer, could confer protection against 5-fluorouracil (5-FU)-induced myelotoxicity in mice. The decrease in bone marrow cellularity, frequency and content of granulocyte-macrophage progenitors (CFU-GM) characterized myelotoxicity in mice, while insulin sensitivity was determined by hyperinsulinaemic euglycaemic glucose clamping. CFU-GM colony numbers increased in groups pre-treated with rosiglitazone (1.5-6 mg/kg, 5 days), compared to that in mice treated with 5-fluorouracil alone. Since rosiglitazone pre-treatment significantly promoted the clonal expansion of CFU-GM when given in the insulin sensitizing dose, we conclude that rosiglitazone had myeloprotective effects possibly by amplifying endogenous insulin action.

Administration, Oral↗