Phenytoin modulates connective tissue metabolism and cell proliferation in human skin fibroblast cultures.

Phenytoin has been proposed for the treatment of certain dermatologic conditions involving connective tissue abnormalities. To understand the biochemical basis of connective tissue changes, we incubated human skin fibroblasts in culture with varying concentrations of phenytoin. The results indicated that fibroblast proliferation, detected by tritiated thymidine incorporation into cells, was slightly stimulated when short incubation periods and low concentrations of phenytoin were employed. However, with longer incubation times and higher phenytoin concentrations, a significant reduction in fibroblast proliferation was observed. Further studies demonstrated that incubation of cells with phenytoin did not affect the production of procollagen, measured as synthesis of radioactive hydroxyproline in the cultures. However, assay of prolyl hydroxylase, an enzyme participating in the post-translational synthesis of hydroxyproline during collagen biosynthesis, was significantly reduced in the fibroblast cultures. The activity of collagenase, an enzyme participating in degradation of collagen, was markedly decreased in cultures treated with phenytoin. Thus, phenytoin may modulate collagen metabolism primarily by affecting the degradation of collagen. The results support previous suggestions that phenytoin may be useful for treatment of patients with increased levels of collagenase, such as in recessive dystrophic epidermolysis bullosa.