BIPHASIC EFFECTS OF MINOXIDIL ON THE PROLIFERATION AND DIFFERENTIATION OF NORMAL HUMAN KERATINOCYTES

Minoxidil is the most used drug with proved effects in the treatment o f androgenetic alopecia (AGA), but little is known about its pharmacol ogical activity and target cells in hair follicles, As AGA is characte rized by follicle atrophy, accelerated hair cycles and hair fiber thin ning, we postulated that keratinocyte proliferation/differentiation is affected and we tested Minoxidil's effects on those parameters. Norma l human keratinocytes (NHK) of follicular or epidermal origin were cul tured in the presence of Minoxidil (0, 0.1, 1, 10, 100, 1,000 mu M) du ring 5-8 days in various media (high-/low-calcium content, with or wit hout serum). Proliferation was assessed by mitochondrial dehydrogenase activity (XTT), BrdU incorporation, lysosome numeration (neutral red incorporation) and total protein dosage. Drug-induced cytotoxicity was measured by lactate dehydrogenase release in culture supernatant, and pro-differentiating effects were evaluated by relative involucrin exp ression (ELISA dosage). On this basis, we showed that Minoxidil had bi phasic effects on the proliferation and differentiation of NHK: Minoxi dil stimulated NHK proliferation at micromolar doses, while antiprolif erative, pro-differentiative and partially cytotoxic effects were obse rved with millimolar concentrations, We can hypothesize that Minoxidil hypertrichotic activity in vivo is possibly mediated by the maintenan ce of proliferative potential in follicular keratinocytes precociously committed to differentiation.