Influence of the extracellular matrix on fibroblast responsiveness to phenytoin using in vitro wound healing models

Recent reports indicate that the topical administration of phenytoin to cutaneous wounds can promote repair. However, isolated skin cells (keratinocytes and fibroblasts) in vitro have varied in their response to phenytoin, giving rise to apparently contradictory results. We have examined how the structure of the extracellular matrix in which human dermal fibroblasts are grown in vitro can influence the response of these cells to phenytoin. The results indicate that, when fibroblasts are embedded within freely-contracting, relaxed, types I collagen matrices, they are insensitive to phenytoin treatment. However, if fibroblasts are grown in collagen matrices which are nonretracting and under tension, phenytoin (5-50 micrograms/ml) significantly (P < 0.01) stimulates cell proliferation, and inhibits collagenase activity in a dose- and time-dependent manner. The fact that the effects of phenytoin on dermal fibroblasts are biphasic and influenced by the surrounding matrix may help to explain why in vitro investigations with phenytoin give rise to inconsistent data. It also suggests that the matrix alterations which accompany wound healing may modulate the effects of phenytoin on dermal fibroblasts.