Flow cytometric analysis of the effect of phenytoin and its major metabolite on mitogen stimulated mouse spleen cells.

The in vitro immunopharmacological effects of phenytoin (PHT) and its major metabolite 5-(4-hydroxyphenyl)-5-phenylhydantoin (HPPH) were investigated by flow cytometric analysis of the DNA content of mitogen stimulated mouse spleen cells. The qualitative effects of PHT and HPPH were similar in concanavalin A stimulated mouse spleen cells with both compounds causing an increase in the percentage of S phase cells. The data suggests that this effect is due to an augmentation of cell cycling as demonstrated by the significant increase in 4N cells in PHT treated cultures relative to control cultures following colcemid treatment. A PHT time course study revealed an increase in S phase cells and a subsequent increase in 4N cells. PHT had no significant effect on congenitally athymic nude mouse spleen cells stimulated with lipopolysaccharide (LPS) except at the highest concentration tested (80 micrograms/ml) where a depression of cell cycling was observed. HPPH caused a colcemid-like accumulation of 4N cells in the LPS stimulated nude mouse spleen cell cultures. PHT and HPPH were found to be effective in enhancing cell cycling in cultures containing a significant population of T-cells stimulated with a T-cell mitogen whereas an inhibitory effect was observed in cultures without T-cells stimulated with a B-cell mitogen. The capacity of PHT to enhance the mitogenic action of concanavalin A may relate to its capacity to induce immunologic abnormalities and lymphadenopathy in humans.