Alteration of bone marrow cell cycle kinetics by diphenylhydantoin: relationship to folate utilization and immune function.

Female B6C3F1 mice were administered the anticonvulsant drug diphenylhydantoin (DPH) for 1 to 4 weeks by gavage at doses of 25 to 200 mg/kg. None of the dosing regimens caused toxicological manifestations other than hepatomegaly. Evaluation of the immune status of the drug-treated mice revealed no alteration of cellular immunity, measured by delayed hypersensitivity response and lymphocyte responsiveness to mitogens or allogeneic leukocytes. Humoral immunity, as measured by serum immunoglobulin quantitation and plaque-forming cell response to sheep erythrocytes, was depressed by DPH at 100 mg/kg after 2 weeks, as was host resistance to infection with the parasite Plasmodium yoelii. The bone marrow was the most sensitive target organ with loss of the multipotent stem cell colony-forming unit-spleen occurring within 1 week at a dose of 50 mg/kg. The colony-forming unit-spleen suppression was the result of a selective loss of stem cells in S phase. Committed granulocyte macrophage progenitor cells, colony-forming unit-granulocyte macrophage, were also inhibited by DPH in vivo, as well as in vitro at concentrations as low as 0.2 microM. Bone marrow cells from DPH-treated mice were folate deficient, as determined by the inability of these cells to convert deoxyuridine to thymidine. However, these mice had normal serum folate levels, even after 4 weeks of treatment. Folic acid protected bone marrow stem cells after both in vivo and in vitro treatment with DPH. It is suggested that DPH inhibits folate utilization or metabolism at the cellular level, selectively affecting bone marrow stem cells and resulting in altered stem cell kinetics. This lesion ultimately results in altered humoral immunity and impaired host resistance.