2'3'-Dideoxycytidine-induced thymic lymphoma correlates with species-specific suppression of a subpopulation of primitive hematopoietic progenitor cells in mouse but not rat or human bone marrow

Comparative toxicity of dithiocarbamates and butadiene metabolites in human lymphoid and bone marrow cells

Apparent differences in the pattern of leukemia risk have been observed between workers employed in 1,3-butadiene (BD) monomer production and those working in styrene-butadiene rubber production (SBR). There are a number of possible explanations for these discrepancies, including differences in disease classification and diagnosis as well as possible quantitative and qualitative differences in occupational exposure between these two industries. This led us to evaluate the possibility that the pattern of disease observed in SBR might be influenced by the presence of an important class of biologically reactive chemicals, dithiocarbamates (DTC), that were present in SBR but not BD monomer production. Therefore, we compared the immunotoxic and hematotoxic activities of DTC and BD metabolites in human immune and hematopoietic cells. Relative to the mouse, human CD34+ bone marrow cells are relatively resistant to the direct effects of BD metabolites, with only the bis-oxide producing any evidence of suppression of clonogenic response at concentrations between 1 and 10 microM. Similarly, treatment of human CD4+ lymphocytes with known (2,3-epoxybutene) and putative BD metabolites (D,L-butane-bis-oxide, (2S,3R)-3-epoxybutane-1,2-diol) does not result in appreciable T-cell toxicity at concentrations likely to be encountered in vivo. In contrast, treatment of human cells with DTC at concentrations as low as 100 nM results in significant suppression of hematopoietic clonogenic response and T-lymphocyte function. Additional studies in our laboratory and others suggest a role for copper in DTC toxicity in both human lymphocytes and bone marrow cells, although the pattern of altered transcriptional regulation observed is markedly different in these two cell populations. These results are consistent with the pattern of DTC toxicity previously observed in clinical and molecular studies.

Comparative toxicity of known and putative metabolites of 1, 3-butadiene in human CD34(+) bone marrow cells

Species-specific susceptibility to the hematotoxic effects of 1, 3-butadiene (BD) is well known. Previous studies have revealed that murine bone marrow is uniquely susceptible to toxicity following exposure to the parent compound in vivo or exposure of bone marrow cells to the monoepoxide metabolite, 3,4-epoxybutane, in vitro. Studies described herein compare the relative ability of putative and known BD metabolites to produce concentration dependent suppression of colony formation and cytotoxicity in human CD34(+) bone marrow cells. Compounds evaluated included 3,4-epoxybutane, D, L-butane-bis-oxide, meso-butane-bis-oxide and (2S, 3R)-3-epoxybutane-1,2-diol. In contrast to results previously observed in mice, only the bis-oxides produced significant suppression of colony formation at potentially relevant concentrations (10(-8) to 10(-3) M). No enantiospecific differences were observed between the meso- and D,L-bis-oxides and no significant lineage-specific differences in susceptibility to inhibition of clonogenic response were observed among early multi-potential myeloid and erythroid hematopoietic progenitor cells. The relative potencies of the bis-oxides were found to be comparable to that of the prototype hematotoxic compound, hydroquinone. These results confirm previous studies that reveal marked species-specific differences in the susceptibility of bone marrow cells to 3,4-epoxybutane. Moreover, these results suggest that the bis-oxides of BD are capable of suppressing the clonogenic function of human hematopoietic progenitor cells, if, in fact, they are produced in human bone marrow in significant concentration. Further interpretation of these findings requires a better understanding of the metabolism of BD in humans.

Dithiocarbamates inhibit hematopoiesis via a copper-dependent mechanism

Dithiocarbamates (DTC), an important class of therapeutic and industrial chemicals, have alternatively been reported to be either beneficial or toxic to the hematopoietic and immune systems. In the present study, we investigated the potential of dimethyl- and diethyl-dithiocarbamate to alter clonogenic response of primary human CD34(+) bone marrow cells in vitro. Our results demonstrate that both compounds are potent inhibitors of clonogenic response in human CD34(+) bone marrow cells, suppressing cytokine-induced colony formation at concentrations between 100 and 500 nM. Pretreatment of bone marrow cells for 1 h with very high doses of DTC (30 microM) had no effect on colony formation. DTCs are known inhibitors of nuclear factor-kappa B (NF-kappa B); however, data presented herein demonstrate that DTC do not inhibit cytokine activation of NF-kappa B in CD34(+) bone marrow cells. Additional experiments demonstrate that DTCs induce a dose-related increase in apoptosis, potentially acting via a cytotoxic mechanism. We further demonstrate that the addition of copper sulfate greatly potentiates the hematotoxicity of DTC and that the addition of a copper-specific chelator completely abrogates DTC clonogenic suppression. These data support a role for copper in DTC-induced hematotoxicity.

Hematotoxicity of the chinese herbal medicine Tripterygium wilfordii hook f in CD34-positive human bone marrow cells

T2, a chloroform/methanol extract of the herb Tripterygium wilfordii Hook f, has been used in China for the treatment of autoimmune and inflammatory diseases for many years. Recent experimental evidence has confirmed that T2 has potent anti-inflammatory and immunosuppressive activity, and a United States Food and Drug Administration-approved clinical trial is currently exploring the efficacy of T2 in the treatment of rheumatoid arthritis. Despite the potential therapeutic benefits of T2, there is ample documentation that T2 is toxic, targeting, among other things, the hematopoietic system, and its use has resulted in cases of leukopenia, thrombocytopenia, and aplastic anemia. This investigation was undertaken to characterize the in vitro effects of T2 on primary human CD34-positive (CD34+) bone marrow cells. Our results demonstrate that T2 has a potent inhibitory effect on the clonogenic response of human bone marrow cells to exogenously added hematopoietic growth factors. The inhibition of colony formation by T2 is not the result of direct cytotoxicity or increased apoptosis and indicates a functional suppression of hematopoiesis. Additional experiments demonstrate that T2 also alters transcriptional regulation in bone marrow cells by inhibiting nuclear factor-kappaB. This transcription factor is found in CD34+ bone marrow cells and has been recently shown to be a requirement for colony formation. These results demonstrate that therapeutic concentrations of T2 exert a significant hematotoxic effect by inhibiting growth factor response in CD34+ bone marrow cells and suggest that inhibition of nuclear factor-kappaB may play a role in the blood dyscrasias encountered with the use of this drug.

An Essential Role for NF-κB in Human CD34+ Bone Marrow Cell Survival

The transcription factor, NF-κB, is important for T-cell activation, B-cell maturation, and human immunodeficiency virus transcription and plays a role in alternatively mediating and protecting against apoptosis in a variety of cell types. However, a role for NF-κB in human CD34+ bone marrow cells has not been described. We provide evidence here that virtually all human CD34+ bone marrow cells express NF-κB that can be activated by exposure to phorbol 12-myristate 13-acetate and a variety of cytokines, eg, tumor necrosis factor , interleukin-3, and granulocyte-macrophage colony-stimulating factor. In addition, we demonstrate that NF-κB may be required for human CD34+bone marrow cell clonogenic function and survival. These results offer insight into a new role for NF-κB in maintaining survival and function in hematopoietic stem and progenitor cells and suggest that proposed strategies involving inhibition of NF-κB activation as an adjunct to cancer chemotherapy should be approached with caution.

Murine thymic lymphoma is associated with a species-specific hematopoietic progenitor cell subpopulation

Many strains of laboratory mouse are uniquely susceptible to the development of T cell lymphoma/leukemia, either spontaneously or as a result of chemical or radiation exposure. In contrast, T cell leukemias or lymphomas which are relatively uncommon in human populations, are not easily induced by radiation, and are not generally associated with chemotherapy or chemical exposure. Evidence is presented to suggest that differences in the susceptibility to the development of these malignancies is related to subtle but important variations in the regulation of hematopoietic stem cell differentiation between these two species.