THE EFFECT OF MINOXIDIL ON KERATOCYTE PROLIFERATION IN CELL-CULTURE

Purpose: To determine if minoxidil inhibits keratocyte proliferation i n a nontoxic manner. Methods: Rabbit keratocytes were cultured in Eagl e's minimum essential medium supplemented with fetal bovine serum. Min oxidil varying in concentration from 10 degrees to 10(3) mu g/ml was a dded to the culture medium and incubated for 7 days. The cultures were inspected for morphologic appearance and the cell number was determin ed at 1, 3 and 7 days after the addition of minoxidil. After 7 days of incubation, minoxidil was withdrawn from the cell culture medium and the cells were examined 3 and 7 days thereafter. In addition, a nonrad ioactive cytotoxic assay was performed to determine if toxicity is ass ociated with the presence of minoxidil. Results: Minoxidil inhibited k eratocyte proliferation in a dose-dependent fashion. 29% of control gr owth was achieved when keratocytes were cultured for 7 days in 10(3) m u ml, whereas 82% control growth was achieved when keratocytes were cu ltured in 10(2) mu g/ml of minoxidil. Intermediate concentrations betw een 10(2) and 10(3) mu g/ml produced a linear decline in cell counts i n a dose-dependent fashion. The concentration of minoxidil required fo r 50% control growth at 7 days extrapolated from the dose-response cur ve was 600 mu g/ml. Upon withdrawal of minoxidil, cell counts returned to baseline for concentrations of 10(2) mu g/ml or less. Phase contra st microscopy revealed that the presence of minoxidil was associated w ith intercellular separation, enlargement of cell bodies and elongated processes. After the withdrawal of minoxidil, the cells in all media reassumed the morphological features of normal keratocytes which inclu ded a regular fusiform shape and extensive intercellular contact. The nonradioactive cytotoxic assay revealed the lack of cytotoxicity at al l concentrations of minoxidil based on a lack of lactate dehydrogenase release. Conclusions: Minoxidil inhibits keratocyte proliferation by a nontoxic mechanism. It might be particularly useful for modulating c orneal wound healing following excimer laser photorefractive keratecto my.